Here, I’m using the basic UNO Logger as a tethered Data AcQuisition device, recording the current used by a second data logger. Since the second logger is ‘floating’ with no connection to the UNO’s ground line, the voltage drop across the 5Ω shunt resistor is recorded using a differential channel on the ADS1115. Differential readings are also useful for sensor applications that use a wheatstone bridge arrangement.

I recently picked up a ADS1115 breakout board, and it was fairly easy to use that with the serial data plotting capability of the Arduino IDE. It’s not often that something works this well on the first try, and I thought I would post about using  the combination as a kind of  ‘poor mans oscilloscope’.   The plotter’s vertical axis auto adjusts as the value of your output increases or decreases, while the X axis is fixed at 500 points, with each tick of the axis equal to an executed serial println command.  Having the ability to spool data to the screen with a simple print statement, turns the exercise into a “What happens if I do this?” kind of process, which is perfect for providing feedback to students learning how to program Arduinos.  I posted the code used to generate these graphs on GitHub, but you will have to noodle around with it to figure out what the threshold settings should be for your particular application.

Although I already have a good method to estimate the overall power consumption of my loggers, I was motivated by this Jeelabs post to see if there was a way I could look at individual events. Even if you have a nice Rigol to play with, it can still be tricky to get all the settings and timings right because the loggers can draw anything from 0.15mA while sleeping, all the way to up to 100mA during SD writing events.  Jeelabs elegant solution to this ranging problem uses two shunt resistors and a diode, but with 15bits of differential range on the 1115, the 8x gain setting can do the job with a single resistor. (…provided I don’t exceed the ±0.5 volt limit that PGA setting imposes…) 

After installing Rowbergs I2Cdev library, and running a couple of jumpers, my drip sensors were generating raw count output like this:

Of course that was scrolling by like crazy, and the re-scale feature meant that the y-axis was jumping round like a bullfrog on a hotplate. You can bring the vertical axis under control by adding a few delimiter separated constants before the final data println:

Serial.print(4000); Serial.print(” “);     // sets a stable upper value line
Serial.print(0); Serial.print(” “);             //this constant sets a stable lower value

But to prevent the x axis from scrolling forever, I had to setup a trigger threshold, that would only capture a new set of readings when an actual event was occurring:

A few runs with text-only output showed the sleeping logger generating around 65 raw counts on the ADC, so I set the LoopThreshold to 75, and the plotter started behaving like an oscilloscope’s triggered sweep: scrolling 500 new readings across the screen each time the drip sensor woke up.  With a known shunt resistance, and the millivolt resolution per bit from the datasheet, I could convert the raw ADC counts to μA in the printing loop. Just for fun I also tried speeding up the I2C bus to see the temporal resolution of that sample loop at 400Khz:

So I was asking for data faster than the 1115’s top speed of 860sps could deliver it.  A few more trials showed that even with the Arduino’s default 100Khz bus, I had to add delayMicroseconds(400);  into the capture loop to keep the UNO from outpacing the ADC module.  I expect that will be different for Arduinos with different clocks like the promini, so one would have to make manual adjustments based on the elapsed times for each system.

These drip logger events are the result of straightforward code that follows the steps:

1) Wake from interrupt & clear the registers, update count variable
2) Turn indicator LED on & sleep for 15ms
3) Wake, turn LED off & sleep for another 32ms (to let impact vibrations die down)
4) Set accelerometer registers & go into deep sleep: wait for next accelerometer interrupt

Since you can drop as many constants on the plotter as you want, it’s easy to determine the current level at a specific point on the plot by intersecting it with a new line:

Though there were no surprises in the pattern per se, it was handy to find out that the “in-event” sleep current was about twice the normal standby state. (which I confirmed at 0.2mA using a DMM)  Now I can go digging through the code to figure out what’s drawing  that extra power.

After resetting I2C bus, I tweaked the delays to exactly match the 860 sps output from the ADC. Then I sat back and waited for one of the real time clock alarms to fire:

This was my first view of that complex logger event, with variable juggling, time stamp creation, eeprom buffering, counter resets, etc. With I2C devices being able to stretch the clock whenever they need to, I had no idea how long these kind of events actually took, and I certainly never managed to capture one so easily on the old clunker scopes I could get my hands on.  The comb pattern you see there is a result of sleeping the processor for 15ms after sending data to I2C device registers; instead of using a 6ms delay while the Arduino waits for the devices to respond.  This lengthens the overall duration of the event, but the time spent running at full power is reduced.

By how much? I reset the logger to use delays after I2C writes rather than sleeps and re-captured the event:

The horizontal axis is at the same scale as before. The start of the event now looks like a solid block and the overall event is about 50ms shorter.  For comparison, I’ve inset the previous graph with the sleep gaps cut out and the spikes moved together, and the two white rectangles at the top represent area equivalent to sleep gaps that were removed.  The grey area shows the power saved by using 15ms sleeps instead of 6ms delays.  To do this properly I would need to take another reading of the 3xAA power supply voltage and calculate the total power used (minus the loss on the shunt resistor), but you can see at least 25% improvement simply by comparing the plots. That kind of feedback is very helpful when you are trying to optimize your code.

Now, I can already hear people scoff that even $3 is too much to pay for a scope that won’t reach 1Khz. Indeed, with a minimum temporal resolution of just over a millisecond, the ADC frequently misses brief current peaks. I know my 8mhz promini based loggers usually draw more than 4mA while running, and you see the longer operations in the RTC/delays event pushing up towards 6 mA.

But even with the upper third lopped off those spikes by timing errors, I can still use this method to make a reasonable estimate of the power being consumed by logger events provided they don’t last more than 580 milliseconds. ( The serial plotter provides a window for only 500 samples and the UNO barely has enough variable memory for a 16bit integer array that size.) If you add the SD card library to your script you are only left with enough memory for about 100 of these samples in your capture loop, although you could try reducing the ADC readings down to 0-256 with a well tuned map function. Then you could use an uint8_t integer array, and store twice as many readings in the limited variable memory of the Arduino.  If you were just doing a classroom demo, that range would probably still give you a decent display on the plotter.

Despite these limitations, the setup is so simple that I think the serial plotter tool will become a go-to for quick looks at sensor data, perhaps even replacing some processing based demos.  The ability to connect four of these ADC modules to a single Arduino makes the platform look quite respectable as a classroom level data acquisition system, especially for environmental data that rarely requires high frequency sampling.  

If you switch to a beefier 1280 based Arduino like the Mega, or the Moteino, those memory limitations disappear and recording much longer events would become possible.  With the delays I had to put in, my gut feeling is that you could juggle a couple of these boards at a time; interleaving the readings to double or triple the effective sampling frequency. (at least until the input impedances start to mess with the shunt resistor…)  And finally, I think adding a couple of well chosen diodes to clamp the input voltage to the ±limits imposed by your PGA setting would be a good idea in the classroom, or you might loose a few of those ADS1115 modules.

It is worth noting that there is a comparator function in the ADS1115 that can be programmed to send a pin change alert when a given threshold is crossed. If I can figure out how to get ADS1115’s built in comparator working with the differential modes, this would even let me put the DAQ to sleep between sampling runs. The ADC module also has a ‘data ready’ alarm that can be enabled to tell you exactly when it has the next reading available.  I did not go that route as the generic approach used here is applicable to sensors without these features, including the ADC built into the Arduino. 

There are plenty of other serial data plotting programs, but using the free IDE version like this is an iterative exercise, forcing you to switch between the serial text monitor & the serial plotter a few times to tweak the delays and constants. If you are using an UNO in a classroom setting, this in itself is a useful activity.  And given how cheap basic DAQ modules are these days, choosing to use an Arduino is always about the showing the process rather than just getting a final result.

Addendum 2016-08-15:     A MUCH faster DAQ with the native UNO ADC

Here I’m reading the voltage across a 10Ω resistor with the UNO’s built in ADC. To do that I need to join the ground lines because the Arduino can only take single-ended readings. That also forces me to put the shunt resistor on the low side line so I don’t exceed the 1.1 vref. This arrangement causes the promini logger’s effective ground line to jump around as the current through the resistor changes.

The folks over at Measuring Stuff  posted a page called The Arduino DAQ Chronicles, which goes into some detail on the process.  It’s a good chunk of background reading even if you are using the ADS1115 ADC described above. The Arduino’s native ADC delivers 10-bit readings, (ie 0-1023) and compared to the relatively pokey ADS1115, a typical UNO can take several thousand analog readings per second; outperforming the ADS1115 by a fair margin. The challenge is balancing the reduced resolution with the other limits imposed by the method itself. Even if you increase the sensitivity of the native 10-bit ADC by changing to the internal 1.1vref, you only reach 1.1v/1024 steps = 1.07 millivolt per bit. Remember that my loggers are sleeping at 0.2 milliamp x 5Ω shunt resistor = 1 millivolt so we are operating right on the lower limit of the ADC resolution. With that 1.1v cap on the ADC input, and a potential 100mA peak current (during SD card data saves), the largest shunt resistor I can use is 1.1v/0.1a= 11Ω. So to get the Arduino to discriminate the low currents we need to use a pretty  large shunt resistor value, and allowing the voltage drop to get that high imposes another challenge in that the drip logger would only be left with 4.5v (the 3xAA battery) – 1.1v drop on shunt = 3.4v. That’s right at the minimum input voltage needed by the 3.3v regulator on the Arduino promini board, risking a potential brown-out in the middle of the SD card writing process.

But hey, lets pop in some new batteries, and see what we get:

Not too bad, but that’s a noisy plot with lots of jitter on the base line. Having 1-2 bits toggle like that is typical for ADC’s so there is probably nothing I can do to get rid of it. And the drip sensors resting state reads at zero when it should be registering at least two counts. It is also common for an ADC to under or over read by a few bits, so I added an offset adjustment into the code to bring that sleeping baseline up to the 0.2mA that I have already confirmed with a multimeter.

Then I realized I still had the 400us delay in there from the ADS1115, so I took that out:

Crikey! Even with the code overhead, that thing is taking over 8000 samples a second! That’s far too many readings for the serial plotter to handle if I want to view long events.  And that first spike goes upt to about 5mA – exactly where it should have been on the ADS1115 readings if that module had not missed them at 860sps.  So how do I maintain the Arduino’s ability to spot those rapid sample peaks, but only send 500 readings to the screen?

Instead of delays, I decided to create an “oversampling loop” that creates a running average using a low pass filter, but also checks for peaks throughout the process. You can dig into the code for this over at GitHub, but the basic idea that is if a peak occurs, then the highest reading in an interval becomes the final reading. If a decreasing trend is found, then the output from a leaky integrator becomes the final reading for that interval. So the readings get smoothed on the way down, but not on the way up.

Here is a try with the oversampling interval set to six ADC readings:

That’s the RTC event (with delays) and the drip triggered event at the same scale.

Now here’s another run with a 15:1 ratio:

Squashing more than 7000 raw readings into a 500 line display really starts to distort the curve, but everything is still recognizable, and more importantly, the peaks did not get chopped off like they did with the ADS1115.  Woot!

Now we have a method that lets us adjust the serial plotter’s display to match the event we are trying to see, provided we don’t over-interpret the accuracy of those heavily averaged interval numbers. And rapid sampling can introduce other issues to deal with. For example: Dustyn Roberts has a useful post on creating very precise time stamps with the micros(); function when you are sampling faster than 1 millisecond. 

So within limits, a standard Arduino gives you good temporal resolution but can not detect less than 1 millivolt of change, while the ADS1115 gives you precision down to an impressive 0.0078 millivolts (@16x gain) but is not so great for tracking really brief events.  If you need both resolution & speed, you need opamp circuits designed for the specific situation, as in the Jeelabs example. It’s also worth mentioning that the Arduino ADC also supports a comparator that you could use for the threshold function more elegantly than I’ve done here.  And with such a low impedance input, you can also double or triple the sampling rate by changing the ADC clock prescalers (this is also in the code on GitHub) Both of those things are described in detail over at Nick Gammons excellent page on ADC conversion on the Arduino.

Addendum 2016-08-16

Hopefully they will add export options (like other serial tools) to the plotter in the future, but for now you can manually copy data out of the serial text monitor and paste it into Excel.  Before you start a long run for export to a spreadsheet, comment out the constants that you were printing to stabilize the plotters y – axis, so that only the numbers you are interested in are sent to the serial output.  If you are waiting for an event to happen, it often helps to add a threshold test so that the serial monitor is not just filling up with uninteresting data that you would have to prune away later anyway:

Then after your DAQ has been capturing events for a while, click inside the serial monitor window,  select all the data & copy it (on a windows machine that would be [CTRL]+[A] followed by [CTRL]+[C] ) then open a new spreadsheet and simply paste the data into an empty column.

This lets you compare the events side by side:

If you want to graph more than one number, then add a comma between them with Serial.print(“,”);  remembering to use println on the last variable being sent.  Then you need to add the intermediate steps of pasting the data into a text editor like notepad, and saving that text file. Then change the ending from .txt to .csv and Excel will open it directly. If you can’t change the filename, you can still import the text file and specify comma delimiters:

to put the numbers into adjacent columns. If you don’t have excel, there are plenty of other data plotting options out there. And programs like coolterm, can save you from having to do those cutting & pasting steps.

Addendum 2016-10-13

Gokul Shrinivas just posted a neat little bit of code at hackster.io that reads the Arduino ADC at a cracking 68k samples per second out of a Arduino Due by directly accessing the ADC ports as soon as the DataReady interrupt is triggered. 

He starts with defines:

#define ADC_MR * (volatile unsigned int *) (0x400C0004) /*adc mode word*/
#define ADC_CR * (volatile unsigned int *) (0x400C0000) /*write a 2 to start convertion*/
#define ADC_ISR * (volatile unsigned int *) (0x400C0030) /*status reg -- bit 24 is data ready*/
#define ADC_ISR_DRDY 0x01000000
#define ADC_START 2
#define ADC_LCDR * (volatile unsigned int *) (0x400C0020) /*last converted low 12 bits*/
#define ADC_DATA 0x00000FFF 

And the sampling loop becomes

ADC_CR = ADC_START ;
  for (i=0; i<320; i++){
    // Wait for end of conversion
    while (!(ADC_ISR & ADC_ISR_DRDY));
    // Read the value
    analog_data[i] = ADC_LCDR & ADC_DATA ;
    // start next
    ADC_CR = ADC_START ;
  }

He used an LCD screen for the scope, but I am wondering if it would be possible to refine my oversampling trick to squeeze that many data points on the serial plotter somehow…

And I wonder if this trick is even available on the 328p? I guess I will have to go looking at other Arduino Oscilloscope projects. The problem is that most of them seem to be using 8-bit signals from “free-running” modes, and I rarely have an application that needs less resolution. Here’s a project doing Interrupt-Driven Analog Conversion  with an ATMega328p, and Nick Gammon mentions it here, but no one does a speed comparison with the ten analog 10-bit readings you get per millisecond using plain old analogRead();

Even if there is no speed gain, perhaps I could do calculations while I was letting the ADC read continuously to speed up the overall sampling loop.  I could see myself getting out of sync pretty easily though, unless I deactivate the general interrupt flag and activate it again (with  cli() and sei()) or I would randomly miss readings.

Nick posted a code example of reading the Analog-to-Digital converter asynchronously that seems to solve the synchrony problem.  He’s also posted an interesting ‘sleep during ADC conversion’ example buried in there, but that’s only useful if you are not using timers & PWM at the same time, and I often do that…

Update: the Hackster.io project listing magically evaporated… and I just found exactly the same code at Bruce Land’s Hackaday project from 6 months ago. So I think proper attribution for the script above should go to Bruce.

Addendum 2017-01-10

I’ve been playing around with the ADC clock prescalars, and with the asynchronous reading code available over at Nick Gammon’s site to try to get better temporal performance out of my little UNO-scope.  With such a low value shunt resistor the ADC seems to read fine even if you crank it up to about 40k samples/second. Unfortunately you pass a point of diminishing returns due to the processing overhead with the interrupt based asynchronous readings,  so async reading actually reduces the number of readings per millisecond at the higher clock speeds. If you want to play with this approach yourself, I’ve posted the update with the prescalar settings to GitHub.

Addendum 2017-02-27

Anyone interested in using an Arduino as at data acquisition device will probably want to see my recent post: Enhancing ADC resolution with Dithering & Oversampling
For an unmodified UNO,  Qwerty’s triangular dither method is probably the easiest one to use, but for 3.3v boards I’d go for the Toggled pin dither method I outline at the bottom of the post.

Addendum 2019-09-27

Microsoft has added a ‘data streaming’ plugin that’s free for Office 365 users which will accept data directly from an Arduino. If you are a student, the 365 software itself is also free. But for those of us running older versions of Office, the cut and paste method described above still works fine.

It’s August, and we’re assembling kits for another run of the instrumentation course.  Over time we have come to rely on 328p based microcontroller boards (aka: Arduinos) so I though I would post a list of the parts & materials we use to help others fire up their own classroom. More than a few people have requested this since I posted the UNO based logger tutorial.

This information should also be looking to buy an all in one solution for their first citizen science project.  Don’t reinvent the wheel if you don’t have to: there are lots of premade Arduino kits out there.  However we found that many had parts we simply didn’t need, as we wanted a minimal ‘starter kits’ designed to exactly match the lessons in a course focused on environmental monitoring.  We also hand out extra parts for some tutorials as needed through the course, and the students receive a second project box when they start building their stand-alone  projects.  Even if you want that level customization, it might worth looking at some basic electronic component kits, and building your classroom set on top of those. The DIY approach will save money, but you pay for it with time.  Most of the eBay parts shown here took about two weeks to ship, with some stragglers taking almost a month to arrive.

You will need more than an Arduino and a few components  to set up a classroom, so I am including tools & other miscellaneous bits of hardware that we use in the lab. I would not describe any of these as high quality equipment, but they are ‘good enough’ to get things rolling on a modest budget.  Even if you go with cheapest possible suppliers – you are doing great if you can run a fully developed course for $150 a seat. If you purchase a soldering station for every single student, and use UNO’s + a typical Pro Mini logger build, you’re looking at about twice that much for the initial run of your course.

Components for the UNO based Datalogger:

UNO Data logger Kit:					$25-50 / seat
	Arduino UNO R3 The real thing, and tough as nails. All of my old UNO R1 boards are still operational despite years of abuse. If you can’t afford the real thing due to budget limitations, then at least donate a few bucks to help them keep the Arduino open source project going.				$24.95
	UNO clone (incl. USB cable) If your budget forces you to go this route, choose clone boards with ATmega16U2 or 8U2 UARTs (like those in the genuine UNOs) to avoid problems with the IDE. If you can deal with the driver issues, there are clones for as little $3 with alternate UART chips like the CH340 – but CH340 UARTS  do not work with Macs.				$7.20
	Transparent Experimental Platform Base-plate Last year we made our own base plates with M3 risers and Plastruct Styrene sheets. But these acrylic boards save a lot of time. Check left/right side orientation of the holes on the board before buying and the ones with the larger threaded nylon standoffs tend to be better options.				$1.50
	Mini Solderless Breadboard 400 Tie-points Get at least two per student, in case they need to expand their projects. The plastic in these cheap breadboards tend to “warp” slightly over time and the adhesive layer on the back is not thick enough to accommodate this bending so they will slowly come away from the mounting surface. If you are attaching your breadboards to acrylic plates beside an UNO – add an extra layer of double sided foam tape to the bottom of the breadboards before sticking them down.				$1.20
	40wire Dupont 10cm Jumper cable An alternative to loose jumpers wires, and they make the student kits look much nicer at the beginning of the term. Have students make longer or shorter jumper wires by hand when they need them to provide practice with the crimping tool. Jumpers you make yourself are always more reliable!				$1.00
	22AWG Solid Hook up Wire Kit One box will cover the entire class and they should know how to cut and strip wires properly. Don’t bother with pre-cut solid core jumper wire sets as the set lengths are almost never the right size. Striveday also sells mixed boxes of solid core wire.				$20.00/box
	Micro SD Card Memory Shield Module This shield is ONLY for UNO based loggers (not the ProMinis) Don’t forget to buy μSD cards to go with them. Test any used ones to make sure they are ok.				$1.00
	DS3231 & AT24C32 IIC RTC Clock Module I have a page describing these RTC board in some detail here. You will also need a CR2032 3v Lithium coin cell backup battery, after you remove the charging circuit resistor. The DS3231-S and -N chips are MUCH better than the DS3231M variant.				$1.00
	3-Colour Rgb Smd Led Module (with built-in limit resistors) There is nothing special about this common cathode 5050 LED module, but it’s easy to remove & re-insert without bending the pins, and the low profile helps it fit in the kit boxes. The 200k limit resistors that come built-in on the green pre-mounted boards give you a current that approaches Arduino pin limits, so it wouldn’t hurt to add another 500-1k ohm on the GND line with these modules for extra safety.				$0.80
	Vetus ESD-15 bent tip tweezers Look for the better quality ones with the rounded ends that come to a sharp point.				$1.00
	10 Compartment Small Part Storage Case To keep all the led’s, resistors, etc. from rolling around loose inside the larger clip boxes. Get ones where the section walls can be removed to make room for longer parts. There’s a range of other cheap fishing tackle and (non-waterproof) compartment boxes available.				$0.70
	Sterilite 1961 – Small Clip Box for Lab kits Expensive, but they survive in a student back pack. You can find $1 clip box alternatives (like the photos at the top of this post)  at your local dollar store.  Various  other clip lock food / snack containers can also be used, and some can even be pressed into service as project housings.				$4.25
	Outdoor Products Watertight Box Measures 3.5 x 6.8 x 8 inches with 1.5-liter capacity so this one is for projects that need a lot of internal space –  it could also be pressed into service as a housing for larger UNO based projects going outdoors ( ie: lots of room for big batteries! ) Also see:  the $6.00 Husky 6″parts bin, 7×5.25×3.5″ Parts Organizer , and 4x4x2 in. Grey Sch.40 PVC junction boxes are another housing option, which are also available with 4 & 6 in. depths.				$6.99
	Plano 3440-10 Waterproof Stowaway (3400 Series) Makes a reasonable “instant” waterproof housing for smaller projects and indicator LED’s can still shine right through: We use these on the Pro Mini based logger build. The actual usable “interior space” of the box is 8.1cm x 15.5cm x 3.5mm, which is just a a bit too small for the 83mm x120mm acrylic platform bases used for the UNOs (you can press them in, but they are very tight – better to cut them down a bit)   Pelican 1020 Micro Cases accomodate that UNO platform easily though they are the luxury polycarbonate option which cost more than 2x as much as the plano box. Polyc does allow you to put display screens and solar cells inside the housing because it passes all of the visible spectrum with little loss. Of course that also means that whatever’s inside the case will really cook (60-90°C) if you leave those housings exposed to full sun. If your build is “skinny” enough, 2″ PVC compression couplings can be used as a housings with pvc plugs at each end. All these ideas require you to add cable glands and wire pass-through connections.				$4.96
	Basic Digitial Multimeter DT-830D We have better meters in the lab (like the EX330 which is pretty good for ~$50) but at $3.00 each you don’t have to worry about students loosing or breaking them. Have replacement 9v batteries on hand, as people frequently forget to turn them off. Expect 1-2% error on all readings and don’t try to measure large resistors in the Meg ohm range (because the meter itself interferes with that reading) . Expect 20% of your order to arrive broken during shipment from China.				$3.40
	UT120C Super Slim Pocket Digital Multimeters Often you need a “shirt-pocket” sized multimeter during fieldwork, and we usually have a couple of these along for the ride. Cheap enough to be expendable, but functional enough for most jobs on site, but again not as accurate as the EX330.				$15.00
	Folding Magnifier (5x) Useful for inspecting solder connections but not good for soldering because you inevitably need both hands to do the work. For the soldering stations we pick up cheap reading glasses from the local dollar store.				$0.55 ea.
Note: The stuff above this line goes into every UNO logger kit, but I am adding a few optional things to this list that might be appropriate for other courses:
	Minimal electronic components kit Even though we don’t use them, I wanted to put this in here as an example of a minimum component package that could be a starting point for your custom kits.				$3.50
	Slightly less minimal component kit Another one that’s almost tempting. Search eBay for ‘Electronics starter kit for Arduino’ and you find oodles of these. If you are only making a small number of kits these might be the way to go. But if you are making six or more, check the basic components list below, as most of the parts in these packages are pennies each if you buy them separately.				$7.70
	6xAA Battery Holder Box for Arduino These will power an UNO for about 40 hours of continuous stand alone operation. You can stretch that out with processor sleeping & other tricks.				$2.45
	9 VDC 1000mA regulated power adapter 5.5mm/2.1mm barrel jack, positive tip. Expect these cheap ones to be noisy as heck compared to the ones from Adafruit. We run most of the UNO based lessons tethered to a USB cable, so these rarely get used.				$2.27
	MB-102 Solderless Breadboard 830 Tie Points They don’t go into the student kits, it’s a good idea to have a few of these longer breadboards around.				$2.00
	Arduino UNO R3 Transparent Case An alternative to the flat platform approach we use  would be to try these in combination with a breadboard shield				$1.60
	Mini Breadboard Prototype Shield With a little creativity you could squeeze low profile components for the data logger onto this if you find an SD card adapter, and an RTC with perpendicular pins.				$1.80

Basic Electronic Components:

Most electronic components can be had for pennies if you buy them in quantity. And the difference between low end parts and name brand stuff can be more than an order of magnitude.  That doesn’t mean that off the shelf kits are a bad thing, it just means that what you are really paying for is someone’s time selecting and packaging it.  That still might be the better option for you if you can afford it.

Basic Components:
	Stanley Removable 10 Compartment Organizer Before you buy a bunch of tiny little parts, you need some way to organize them. I usually put the items into 3″x 5″ or 4″x 6″ bags, which then go into these compartments.  Pink 4Mil Anti-static Poly Bags come in all sizes, and work well for this. Being able to remove the section boxes from these organizers to lay out specific parts for a tutorial also comes in handy.  See: Organizer Bin Storage Unit See: Stacking organizers See: Tool Storage				$17.00
	Stanley Shallow Organizer, 25 Compartment This organizer is better for really small components & IC’s that you only have a few of, but you still need to bag them or they get jumbled.				$12.00
	ELENCO WK-106 Solid Hook-Up Wire Kit 22 AWG 22 AWG works reasonably well with breadboards, get at least 6 colors/150 feet. Remember to specify how much to cut from the spool in your lab instructions, or your students will pull 2 feet of wire from the box when they only need a couple of inches on the breadboard. Get two boxes at the start of term.				$19.00
	26AWG Silicone Cover Stranded-Core Wire – 2m This high strand count wire from Adafruit is the nicest stuff you are ever going to work with, and is my favorite after trying just about everything else on the market. Simply fold & cut those pre-cut 2m lengths four times and you end up with 12cm lengths which are perfect for including in kits. [Colors:Red,Black,White,Yellow,Green,Blue,Grey,Orange]				$0.50/m
	60m/box 26 AWG 10m x 6 colors Cbazy / Striveday Silicone Jacket Wire As your projects get more advanced you can never have enough different colors of wire. And there are other box sets to add Orange, Brown & Purple . The thing to watch out for with wire sourced from eBay wire is that some vendors sell crappy seven-strand wire,  which will not stand up to frequent bending like the highly stranded Adafruit 26awg. I also keep some thinner 28AWG and 30AWG wire with high strand count around for finer soldering jobs (eg  here)				$17.00/box
	CBAZY Stranded Hook up Wire 26-30 AWG Flexible Silicone Wire (108 Feet) You can never have enough of certain colors, so I always order extra 30m rolls of RED & BLACK wire for battery connections.  [Colors:Red, Black, Blue, Brown, Green, Grey, Orange, Purple, White, Yellow]  16-30awg available. ~$0.33/m				$12/30m
	1/16″ 2:1 Clear Heat Shrink (MIL-I-23053/2, class 2) Unlike normal heat shrink, mil-spec is very thick and holds its shape after cooling; making it easier to route cables in a housing. Watch for eBay vendors that advertise mil-spec, and send you the thinner cheap stuff.   I think of 1/16″(=1.5mm) heat shrink as “1-wire sized”, 2mm = “2-wire size” and 1/8″(=3mm) as “3-wire size” when working with 26awg. Always buy clear heat-shrink tubing for the classroom – so that you can see when poor soldering has caused a problem with the circuits.				$12.00/100ft
Resistors: Lead diameter makes a resistor breadboard friendly or not. You generally want 0.6 mm not 0.4mm leads, though it is inevitable that you will end up buying a few cheap multipacks with the thin leads. ( Note: You can add male DuPont crimp ends & a bit of heat shrink to components with thin leads to make them breadboard friendly : see inset photo) Brand-names like Vishay, Xicon, KOA Speer are usually very good, but you pay 2-10 cents each for them, and the Vishay leads are sometimes thick enough that you need to cut them at an angle just to insert them in the breadboard.  (Often you can find new-old stock bag lots of Xicon carbon resistors on eBay reasonably cheap)  The cheap old carbon resistors often tend to have thicker steel leads while the better brands have softer copper leads which bend more easily. I find 1/4 watt to be the most practical size and 1/2W metfilms are physically about the same size as 1/4W carbons. Beige-background carbon resistors seem to be much easier to read than blue-background metals, but if you need 1% tolerances, you won’t have much choice. 1/8watt metfilms are very tiny, which can be helpful if you need to put a resistor into a small place, like between two pins on a breakout board. Wherever possible, buy 1% tolerance (or better) resistors, rather than 5%, as this affects your sensor accuracy when you use them in voltage dividers – which is a common way to read sensors.
	130 values 1-10MΩ 1/4W Metal Film Resistors Assortment Crappy thin leads, but a huge range of values to have on hand at the beginning of a class – in fact I would order two of these to get started.   Then order 50-200 of the individual resistor values as needed for your labs/exercises. Be prepared for it to take 2-4 weeks for resistors to show up if you order them via eBay.				$10/2600pc
	MetFilm Resistor 1/4W 0.25W ±1% [Various Sizes] 100 pc of specific sizes with thin leads. We usually put five to ten of 330Ω, 1K, 4.7K & 10K in each kit, but you can tune this to your curriculum and/or hand out other specific sizes at the beginning of each lab.  After you get better at soldering, you will probably switch over to 1/8 watt resistors, as their smaller size lets you put them into tight spaces: like between the pins on a promini board. Also note that metal film resistors use a 5-band code to indicate their value, rather than the 4-band you see on carbon resistors. But we teach students to always check resistance values with a DVM to catch manufacturing errors, and because it’s quite common for them to cook their resistors, or bend the wires too much & break the connection,  when they are just learning to solder.				$1.89/100pc
	1/2W Carbon Film Assortment (30value x10pc 1-3MΩ) Sometimes the 1/2 watt size is easier for beginners to handle. It also helps to have “exercise specific” resistor values look physically different from the other resistors in the kits. These still have thin leads though.				$3.80/300pc
	Carbon Resistor 1/4W 0.25W 5% [Various Sizes] Just a typical eBay search link to give you an idea what’s available. Usually these carbons have nicer thicker leads but the quality varies. Check for free shipping.				$1.00/100pc
Components: Most hobby market parts distributors have “Assortment Kits” for commonly used components and its a good idea to just buy a selection those when you are starting out. It might be a while before you actually dig into that mixed bag of capacitors for the odd value you need for that circuit you just found on the internet, but when it happens you will be glad you spend that $1 six months ago. Where to buy them: I’m going to list several kits from Electrodragon as examples, but there is nothing special about them and you can often find a very similar sets on eBay for significantly less. A common problem with all the overseas suppliers is that it usually takes 3-4 weeks for stuff to arrive, and that can stretch to 8 weeks. So if you realize that you need something quickly, go to Sparkfun/Adafruit/Pololu/Amazon etc and just pay the $15 delivery charge. The thing that makes this complicated is that now a lot of domestic websites like Amazon, Digikey etc, often just acting as distributor for these exact same components from China. Another draw back with Amazon is that those easily recognized boxes are big targets for porch thieves. My rule of thumb with dodgy flea market sites like Banggood, Dealextreme, AliExpress, etc. is: “If this order never arrives, how unhappy would I be about that?” If the answer to that question is “Quite a bit” then you should order that part from a reputable vendor.  More than 95% of the things I order from eBay do arrive…eventually…though it’s common for things like sensor modules to be significantly different than the photos shown in the listing. Overseas suppliers are best used where fakes are unlikely (or don’t matter) like resistors, LEDs, displays, pin headers, switches, wires, vanilla transistors, battery holders and similar items. Or a one-time thing you just want to play with to see how it works. For more complex sensors and microcontrollers it’s very easy to get counterfeits or rejects that kinda seem to work initially, but are way out of spec. In those cases I’m prepared for a percentage of duds, and so far I’ve only had one out of maybe 30  purchases. The cost of returning is usually more than the item’s worth, so you have to be prepared to bear the loss. There are even some complex components I wouldn’t buy anywhere else like the ESP’s, since these are manufactured in Shanghai, so you wouldn’t find these cheaper somewhere else.
	5mm LED Light Diffused Assorted (5 Kinds*20PCs) Having the colored plastic makes it easier for students to identify which LED is which. [red, green, yellow, blue, white]				$1.80/100pc
	LED diffused RGB 10MM Common cathode Having the RGB led a different physical size from the one-color LEDs makes it easier to identify them in the kit. Common cathode means you can use one limit resistor on the ground line. You can use a CR2032 coin cell to identify which leg is which color quickly by putting the common line on the negative side of the battery.				$2.65/10pc
	Ceramic Capacitor Assortment (10 Kinds x 50 PCs) The most important thing to know about ceramic capacitors is that they have the worst thermal coefficients of any component you are ever going to see.  So to build a circuit which will work in real-world environments you need the dielectric to be rated at X7R (±15% from -55 to 125C) or better.  Garden variety Y5V (±82% from -30 to 85C) caps also loose about 30% of their capacitance in their first year of operation (X7R’s loose <10%) and you need to compensate for that too.   And finally you need to buy caps rated for 50v, if you want to use them with 5v because the bizarre rating system means that you could loose up to 80% of the rated value as you approach the rating on the label.				$11/500pc
	100PCs Ceramic Capacitor [30pF,10nF,100nF] The four most common sizes of capacitors to keep on hand are 10μF (106), 1μF (105), 0.1μF (104) and 10nF (103). Get 100 of each to start, as they are frequently used for bypass/decoupling. Most of the time you will be using: 104 (100nF) but like resistors it’s handy to have small mixed assortments on hand for one-of builds.				$0.80/100pc
	Electrolytic Capacitor Assorted (0.22UF-470UF, 12Kinds) I rarely use these (unlike the little ceramics which get used all the time) Keep an eye on polarity because electrolytics (and Tantalum capacitors) will explode if you put them in backwards. There are other kinds of capacitors out there, and for sensor circuits that have to be stable with temperature, or over long periods of time, plastic film capacitors are often a much better choice than either electrolytics or ceramics: I use Polyphenylene Sulphide (PPS +/-1.5%) or Polypropylene (CBB or PP +/-2.5%) when I can since their aging rate (expressed as % change /decade hours operation) is negligible. The only drawback is that they are relatively large, so for a given value, the film cap might be the size of a jellybean, when the equivalent ceramic cap would barely big enough to solder to without a magnifier lens.				$3.30/120pc
	General Diode Pack (8 Kinds) (1N4148 -25PCs, 1N4007 -25PCs, 1N5819 -10PCs, 1N5399 -10PCs, FR107 -10PCs, FR207 -10PCs, 1N5408 -5PCs, 1N5822 -5PCs)				$3.00/100pc
	50PCs Diode [Individual types] 1N4148 is the bog-standard signal diode so it might be worth keeping some of those on hand. When losses matter @ low voltages and low currents, it’s better to use 1N5817 Shottky’s (ie: for things like isolating battery banks from each other)				$0.75/50pc
	Common Zener Diode Pack, 0.5|1W, 3.3V-30V (14 kinds, 5pcs each) Each Zenner has a specific breakdown voltage, so it might be a good idea to wait till you know which ones actually need and order only those specific types.				$1.70/140pc
	General Transistor Pack (17 Kinds x 10PCS, Low Power) Like Zenners, there are many different flavors of transistor out there, and you should figure out which one you need before buying too many of them. So perhaps just order this pack as a backup, and wait till you know which specific ones you need. For example: the 2N2222A is one common NPN BJT that most everyone seems to use, and they are about a penny each.  See: Building a Friendstrument. See: Transistor as a Switch  See:TransistorCalculator.       Rule of thumb for using cheap transistors as switches:  Size your base resistor to make the base current twice the calculated value for the smallest hFE you see listed in the data sheet (see calculator here) provided that does not exceed ~20mA digital pin current on an Arduino. Don’t forget to add pull up/downs for stability. Note: E-B-C pinouts are not standardized For most 2N2222s, when the flat side is facing you, the pins are E-B-C but some  are C-B-E.  If  you get C/E reversed the transistor will still sort of work but with a lower β (beta). This is highly annoying to debug…      To test an unknown transistor with a DVM in diode test mode, attach the red positive lead to the base of the transistor, and the black neg. lead to each of the two unknown legs in succession: The slightly lower of the two voltages will correspond to the collector-base junction, and the slightly higher reading will be the emitter-base junction.				$2.60/170pc
	2N7000 TO-92 N-Channel Mosfet (200mA max) These mosfets are like “Transistors for Dummies” and work great as digital switches when connected to 5v Arduino digital pins – and you don’t have to do the calculations for the base currents, etc. So they are much easier for beginners to use although they will set you back a whopping four cents each. Note: A 100K resistor between the gate and ground keeps the N-fet off by default, but you can generally operate mosfets without a pin-gate resistor, though many recommend 150 ohms there. N-channel mosfets are usually placed on the ground side of the controlled circuit. Note for 3.3v systems: The 2n7000 can be used with a 3.3v Arduino to control things like LED’s, but they only pass between 30-60mA because the controlling voltage (Vgs) needs to be at least 4.5v for the 2n7000 to be fully turned on. With only 3.3v control, the resistance across the 2n7000  is ~ 3-4 ohms, so there will also be substantial voltage drop across it.  Although “logic level” is not exactly as standard term, mosfets designed to work with 3.3v mcu’s often have an “L” in the part number, ex: IR540 (non logic level) vs. IRL540 (logic level).  Ideally you want the MAX value for Vgs(threshold) to be lower than 2.4v in the datasheet, or you want to see an RDS(On Resistance) quoted for 2.4v, or lower.  When considering the On Resistance, calculate the voltage drop that will occur when the MOSFET is On and the load is operating. If the load draws 50mA, and the RDS(on) is 3 ohms, the vdrop across the fet is 0.05*3=0.15v. The tricky thing about this calculation, is that the On resistance changes with the level of the controlling Gate Voltage, and as you get closer to the Vgs(th)threshold voltage, the on resistance increases – so you need to dig into the graphs on the datasheet to figure out what the actual vdrop is going to be. Since the whole point of using a MOSFET as a switch, is to achieve lower Vdrops than you would get using a BJT, you want the vdrop  across the FET to stay below 0.25v maximum.   Probably the closest thing to a 3.3v version of the 2n7000 would be one of the Supertex TN0702 or TN0604, which come in the same TO-92 package. They can’t switch much current, but if you are careful it is possible to control parallel mosfets for increased capacity.  You can solder legs onto SMD parts to make them breadboard friendly. Most of 3.3v N-channel mosfets come in tiny surface mount SOT-23 packages:  The Philips pmv30, pmv31 and pmv56, and the Vishay Si2302, Vishay Si2356DS  , Si2312BDS (or Si2333DS /DDS for P-channel)  The Fairchild NDS331 / 335 is another good option with very low on resistance and a gate threshold of only 1v.  The problem is that none of them are available in breadboard friendly TO-92 packages  so  you might have to mount them on SOT-23 adapter boards to use them, and if you willing to do that it might be worth going to the Si4562DY which gives you both N & P channel mosfets in the same package. A P-channel mosfet is used on the positive side of the load whereas an N-channel mosfet is used on the negative or ground side of the load. When triggered, a P-fet connects the input on the load to the positive source whereas an N-fet (usually) connects the load to the ground line. Keep in mind that you can’t drive a p-channel directly from an Arduino if the circuit being switched is a different voltage from the control logic, but that can be solved by using an N-fet to invert the control signal at low voltage, then connect that to a P-fet on the higher voltage side. Also see: P channel FDN338P and N channel FDN337N, STN4NF03L.				$2.00/50pc
	10K Linear Rotary Potentiometer 15mm Also available in other values like 1K These B1k/10k’s can be put right onto a breadboard if you take a moment to twist the tabs so they don’t over-stretch the breadboard springs, though they are also good for soldering lessons and then you are ready for the ever popular LED Bar graph tutorial at Arduino.cc   Expect a few duds per batch with these cheap ones.				$2.60/10pc
	Breadboard trim potentiometer 1 & 10K These guys are really nice to use on a breadboard as you can turn them with your fingers, however they are more than a buck each. If you can stand using a screwdriver to adjust, the cost of a smaller trimpot goes down to about 20cents each. There are also 3296 Assortment packs of other styles available.				$1.25
	Push Button Momentary Switch (12x12x7.3mm) 15pcs with a selection of different color caps. Cheaper if you get larger quantities. Sometimes there are little bumps on the bottom that you have to snip off to make them breadboard friendly.				$3.70/15pc
	Latching Push Button Switch DPDT 8x8mm I prefer these latching push buttons to slide switches because they are less likely to pop out of the breadboard by accident when you are using them.				$3.00/15pc
	2.54mm 40P Break Away Pin Header [Female/Male] Get both male and female sets. You frequently need to add male header pins to sensor breakout boards.				$0.80/10pc
	Double Length 2.54mm M-M Header Pins Extra long header pins are handy at times, as are 90 degree lateral pin headers				$1.60/10pc
	40 pin Dupont wire jumper cables 20CM M-M, F-F & M-F. Usually you tear off a strip with the specific number of wires you need for a particular situation, like adding a jumper cable to a UART module that did not come with one. Often it’s convenient to buy these cables without the black plastic end covers so you can tear off ribbon strips to make custom cables, but you pay more for that. Those shrouds can be purchased in any combination from 1-8pins wide so you can make your own sensor connectors.				$0.99

Basic Sensors:     (also see: Adding Sensors ( & Modules ) to Your Arduino Data Logger)

With so many different types of transducers, I can only list a few examples here. And rather than a strict definition, I think of a sensor as ‘basic’ if it’s fairly easy to get the output you are after when you connect it to an Arduino. That can happen for different reasons: (1) Sometimes the raw sensor is electrically simple, such as ‘modulating’ sensors that change their physical properties (like resistance) in the presence of heat, light, etc. and these can easily be turned into a voltage with a simple divider. Some of these sensors are ‘self -generating’, producing a small signal which can be fed directly into the Arduino’s input pins. (2) Others fall into the basic bucket because someone else has put the sensor and some fancy electronics together inside an IC package or onto a cheap breakout board/module, to make connecting to the Arduino easier than it would be with the raw sensor. (3) And other times it’s because someone has released an open source “library” that teaches your Arduino to “talk” to the sensor, which might be more electronically complicated than the Arduino itself. (Although sometimes those sensors tend to have so many settings to take care of when you start them up, that even with a library they still end up the “Advanced sensor” category. We have tutorial pages discussing how to use those more advanced sensors.)

Basic Sensors
	Magnetic Reed Switch Perhaps the most fundamental type of sensor is a switch. You can think of push buttons as crude pressure sensors, and magnetic reeds as proximity sensors. They show up in applications like rain gauges and anemometers because they are robust and draw no current most of the time. Find a good tutorial on pull-up resistors, and de-bouncing is another important issue with switch sensors.				$1.00
	5528 Photocell 10KΩ LDR This light dependent resistor might be the easiest sensor to start your lessons with. Put a fixed 10K resistor in series and read the middle of the voltage divider with a analog pin. That’s it. Add a passive piezo buzzer module and you are ready for the popular Light Theremin exercise.				$1.00/20pc
	NTC Thermistor 10KΩ B=3950 1% tolerance Thermistors change their resistance with temperature just like LDR’s do with light. So you use the same electrical circuit to read them as the LDRs. The devil though, is in the details. Thermistors are very non linear, so you need to so some fancy calculations to translate the analog readings into an actual temperature. There are lots of great tutorials out there to help with that. Generally, I prefer to use 100K NTC thermistors, since they have less problem with self-heating.				$1.00/10pc
	Force Sensitive Resistor 0.5″ In this case the resistance changes with applied pressure. In fact there is a whole family of Force / Stretch / Bend sensors like this and they get used for all sorts of things like measuring water level. Unfortunately they are also pretty darned expensive, so sometimes its better for students to make their own FSR sensors instead.				$6.95
	Piezo knock/bump Sensor 27mm Piezos can generate significant voltages, so they get connected with a shunt resistor to damp things down; protecting the Arduino. Be sure to get the ones with the lead wires already soldered on.				$2.60/20pc
When you move away from raw sensors, there seems to be a bewildering array of ‘breakout boards’ and ‘sensor modules’ for the Arduino and they sell them in mega bundles of twenty, thirty or sixty different pieces. Like the component kits it is probably OK to get one of these when you are starting out; just to play with them and see which ones fit your curriculum. Watch for custom connectors that force you to buy extra cables & interface boards. I actually like the Grove System, and similar systems like the Itead Electronic Bricks, but from a teaching point of view those are better suited to creating ‘snap together’ lessons with younger students. (or no wiring at all if you populate a Multi-sensor Expansion shield) That’s not so good if you want them to become comfortable making their own circuits on a breadboard.
	37 in 1 Sensor Modules Kit Just an example of one common module set from eBay. So you will have to hunt around for a set that looks interesting to you, and it might be worth an extra buck or two to get one that comes with an organizing case. For some, like the Keyes series, you can find pinout guides and instruction wiki’s There are usually several “How to use it” tutorials for each sensor at instructables.com and on YouTube.				~$20.00
Once you get a closer look at them, you’ll notice that most of these cheap sensor modules look the same: That’s because at least 50% of those boards are simply a voltage divider like you would use to read the raw sensor connected to one input of a 5 cent comparator circuit. While a 20 cent trimming pot sets the voltage on the other input: These boards take an analog voltage, compare it to a threshold, and then produce a digital on/off output on Dout which you would read on digital input pins on the Arduino. Essentially turning an analog sensor into a kind of switch. This is such a generic circuit, that you could put other resistive sensors on those pins and it would work fine.  Look for boards that give you the 4th analog output pin if you want to read the actual sensor value with the ADC.
	Photoresistor Sensor Module for Arduino Here is that same 5528 LDR I listed at the beginning, being sold as a “sensor module”.				$1.00
	TCRT5000 Reflective Infrared Emitter&Sensor Pair (Raw)				$1.00/10pc
	TCRT5000 Reflective IR Switch (module) Sometimes used for line following/distance sensing in robots.				$1.00
	HR31 Analog Resistive Humidity/Temp Sensor (Raw) You get one combined Humidity/Temp impedance number out of this sensor, which you have to decode to work out the humidity.				$2.75/2pc
	HR31 Analog Resistive Humidity Sensor Module Be careful which one you order. 3pin=On/Off threshold output only & 4pin modules will let you read the analog output of the divider. By now I hope you see the pattern in these cheap sensor module boards. The list goes on forever…				$3.00
	HC-SR501 PIR (Passive Infrared) Motion Sensor This module has vastly more complicated supporting electronics than the simple comparator boards above, but you use it in essentially the same way. Adjust some trim pots and then look for High/Low output on a digital pin.				$1.00
	Capacitive touch sensors Tons of these on eBay, and dirt cheap, but nowhere near as much fun as making a really big capacitive sensor yourself with some flat sheets of aluminum foil and the Arduino capsense library.				$1.50
In addition to modules, you also run into integrated circuit sensors where more electronics are embedded inside the sensor itself. These can have either analog, or digital output, but the digital output is no longer limited to simple on/off information . Analog sensors are generally easier for beginners to use, since all you have to do is read an ADC pin to get your numbers. The digital sensors have to “talk” the Arduino, and that usually involves including a library at the start of your sketches to handle the low level details of the serial communication protocol. There are far to many to cover here, so I will just leave you with a comparison of two sensors that have nearly identical sensing capability, with one being analog, and the other as digital. Equivalent pairs like this exist for other environmental parameters like pressure, humidity, etc.
	TMP36 – Analog Temperature Sensor Unlike a raw thermistor, these sensors have a bunch of circuitry for amplification and signal conditioning so that the output given to the Arduino’s ADC is beautifully linear.				$1.50
	DS18B20 – One-Wire Digital Temp Sensor This ‘one-wire library dependent’ temperature sensor is often the first one people use when they make that transition, and it is one of my personal favorites. Digital sensors come with various serial communication protocols, but in return for the added code complexity you get the ability to hook many sensors to the same ‘bus’ wires, and in the case of the DS18b20, those can be up to 100 meters long.  DS18b20’s are also commonly available on 1m cables inside waterproof metal housings which can be quite convenient for a student project that needs to measure several different temperatures. However if you actually do want them to operate under water, I’d recommend adding another full layer of marine grade adhesive lined heat shrink over the sensor-cable connection because the potting job on the cheap ds18b20s can be pretty badly done. Cheap eBay sensors can also be outside the +- 0.5C spec, but that can sometimes be useful when teaching a lesson on calibrating temperature sensors.  The real thing to watch out for is the sleep current – DS18b20s should automatically go to sleep around 8 nA. If you measure more than that the sensor is probably a dud, that will mess up it’s own readings by self heating.				$1.30
Making the transition from simple analog to true digital sensors is like earning your merit badge with the Arduino. There is usually a digital version for every different kind of analog sensor at about the same cost, and in some cases the digital version offers tremendous advantages in terms of resolution. But one of the first things you want to know is: Are there good libraries to make this sensor work with an Arduino? While there are plenty of independent coders posting open source libraries to GitHub, suppliers like Adafruit & Sparkfun often release them in conjunction with a cool new sensor, and it’s one of the reasons why people in the Makers movement like them so much. Though I have listed several low end commodity parts here, I still spend a significant amount at those first tier vendors: both to get sensors I can rely on, and to show them some love for all that hard work.  For a more detailed discussion of these options see our page on Adding Sensors ( & Modules ) to Your Arduino Data Logger.

Tools:

Before the comments fill up with dire ‘You get what you pay for…’ warnings, I’d like to point out that when I’m buying tools for myself, I check three places: Adafruit, Sparkfun, and EEVBlog. If you want quality tools go there and buy what they recommend because they really know their stuff. However in the real world a teacher is lucky if they get $500-1000 to spend on materials for a 10-12 student class.   See: Collins Lab tool video.

Soldering Stations:					~$130 / station
	Yihua 936b soldering station Unlike thin pencil style irons, These guys have enough thermal mass to handle soldering beefy connectors. Get the ones with the switch on the front and the blue metal stands. Buy a full set of replacement tips at the start of each term – you will need them.				$23.00
Comment: I love my Hakko FX-888D, in fact I wish I’d bought that before working my way through a bunch of crappy soldering irons. However you can buy four of these cheap 936b knock offs for less money, and that really helps the budget if you need enough for a whole classroom. It also helps that these things are big & ugly if you are working in a place were things tend to grow legs and walk away on their own. As an FX888 surely would…
	Replacement handle for Yihua 936 station Yes, soldering irons do break if you drop them, or if a student leaves them to cook for a couple of hours at the maximum heat setting – especially these cheap ones. This is 5 connector handle is not the same as Hakko 936.  And with spare handles this cheap, it’s much faster to just change the whole handle when you want to work a different tip, rather than waiting for the tip sleeve to cool down, and re-threading.				$2.77
	12pc Soldering Iron Tip set Hakko 936 (& Yihua) The ultra thin pointy tip that comes with the 936b is nearly useless.  900M-t-1.2D ‘screwdriver’ and 900M-T-B ‘cone’ tips are not bad for beginners, and it’s cheaper buying those in these 5-packs after you get one “mixed set”. Of course these are all fakes:  real Hakko tips usually cost around $10 each.  Because I do a lot of fine work, I’ve been using the  T18-S4 ‘conical sharp’ (which came with my Hakko 880) as my default tip for many years. It’s not great for heavy jobs, but if you need to work at the level of a IC chip leg the T18 is a good choice. Genuine tips usually have laser engraved markings on the sides. Do not buy lead free tips unless you are using lead free solder, as the chemistry does not mix with sandard 40/60 tin/lead and you end up with a weird blue-green rind forming on the tip.  Remind your students to always apply fresh solder to the tips before turning off the iron, because once they go dry the tips are often ruined. Sometimes they can be brought back to life with tip-tinner.				$9.85/12pc
	Thermaltronics TMT-TC-2 Lead Free Tip Tinner (20g) in 0.8oz Once tips oxidize from running hot and dry they will not hold solder and become impossible to work with. Dunking the hot tip in this compound a few times ( & scraping clean again) will bring many of those abused tips back to life.				$9.00
	Soldering Iron Tip Cleaning sponge And you will need some replacement sponges eventually.				$2.80
	Metal Iron Stand For 936 Soldering Station These lunkers are much more stable than the flimsy wire ring style holders & work with most cheaper irons.				$5.00
	400G 0.8mm 60/40 Rosin Core Solder Wire A large roll like this is for soldering stations that you don’t have to take down at the end of each class. But it should last quite a while.				$17.00
	Solder Wire Holder for large rolls A holder for the large solder rolls like the one above. There are better looking ones out there a few dollars more..				$5.00
	0.6mm 60/40 Rosin Core Solder Wire I use  0.5-0.6mm wire for things like pin headers and general solder joins. Buy a few per station, as small 50 gram rolls get used up quickly. For really fine work on IC chip legs, it’s also handy to have a roll of 0.3mm around.				$1.50
	Solder Removing Wick 3mm braided Get a couple for each soldering station.				$1.50
	SYB-46 270 Tie-point Breadboard I put these single rail protos into the soldering kits as “sacrificial”  breadboards that the students can use to hold header pins in place while pinning up pro-mini boards and sensor modules.  Write “FOR SOLDERING ONLY” in a black sharpie on the boards, because once the heat’s been on them, they are pretty much useless for anything else.				$1.90
	MG Chemicals 8341-No Clean Flux 10 ml Syringe Doesn’t make a mess like the $1 options from eBay, easy to pack up & lasts for years without drying out if you remember to put the cap back on…which students never do…				$10.00
	Heaterizer XL-3000 Heat Gun A cheaper option than a full re-work station, but also much noisier. Also available on eBay				$13.95
	Panavise Jr. – PV-201 This is one of those rare items for which there really aren’t any other equivalent products on the market – though you could try the attaching a PanaVise 207 Vise Buddy Jr (made of plastic) to a DIY base. Don’t forget the Neoprene Jaw Pads and the Speed Control Handle which add a lot to the functionality. As would one of these things.				$28.00
	Third Hand Soldering Stand / Holder I use these guys to hold wires in place, while a Panavise holds the board I am working on. The alligator clips always fail with time and there are other things that might also do the job. At EMS labs, they make their own with thick wire. Hobby Creek Helping hand Arms work pretty well as third hands on their own, or you can attach them to a baseplate. Snap Flow coolant hoses also work, and Julian Ilett makes good use of Blue Tac to hold parts in place while soldering.				$6.00
	Assorted 2:1 Heat Shrink Tubing Kit You rarely use the larger sizes, but a general assorted size kit like this is good when you are starting out. It is much easier to spot soldering problems if you use CLEAR heat shrink tubing but its not as pretty. Keep a good stock of 1.5 mm, 2mm and 3mm on hand, in fact buying those smaller sizes by the roll might be a good idea.				$3.10/328pc
	3.25 diopter Reading glasses The cheapest dollar-store option for close-up soldering work. And get hard shell cases so they can just be tossed into the station kits without scratching.				$2.00
	AWG 30-20 Precision Wire Strippers Hakkos are the gold standard, but these ones from H.Depot are ok. They gave the Ideal T-stripper model 45-121 a good review over at the EMS blog.				$4.71
	#170 Flush Side Shear Cutting Pliers Again the Hakko CHP-170 would be my first choice, but these work.				$2.00
	Bent Nose Jewelry Pliers You can find others for a buck if you go hunting, but I like the handles on these. If the budget allows, also get a few extremely pointy long-nose pliers.  It is often helpful to be able to bend one wire into a tiny eyelet shape before soldering it to a pin, and you need a fine-tip pair of pliers for that.				$2.50
	Plastic Locker Bins with Handles Reasonably large plastic bins let you pack up the soldering stations after class and put them in storage. Most dollar stores have something like this on hand.				$1.00
Comment: Even if you teach the course with breadboards, you will need at least one complete solder station for things like adding header pins to your breakout boards. A full set like this will set you back about $130, and but depending on your scheduling, you might get by with one full station for every two or three students. We usually set them up around the perimeter of the classroom.

Other Useful Tools:
	SN-01BM Dupont Connector Crimping Tool If you keep your eyes open, you can find them for less than $20.00. Many recommend the better quality PA-09 crimping tool, but those usually run ~ $50.00				$25.00
Make non-reversible  connectors by  combining M&F pins Comment: Before you get a crimp tool, you have no idea why you would want one. Afterward, you use it almost as often as your soldering iron. Dupont connectors are ubiquitous and lots of electronic components have leads too thin to use on a breadboard, so you end up crimping male DuPont ends onto them just to plug them in. It does take a bit of practice to get the hang of it, but there is no other way to make interconnecting cables this quickly & inexpensively. See Instructible: Make a Good Dupont Pin-Crimp Every Time
	Dupont 2.54 Connector Crimp Ends Be sure to get both Male and Female ends. Buy 2x as many female as male pins.				$1.52/100
	Dupont Jumper Plastic Terminal Ends Get at least 200: 2x, 3x, 4x and 6x plastic covers. I don’t use the 1x ends any more, as I simply put black heat shrink over them. There are and infinite number of other cable variations that you can build.				$0.90/50pc
	50mm Solder Pot Once you start building things you end up having to tin allot of wire ends, and a solder pot makes that much faster than using your soldering iron. You only need one of these per lab, and you could probably skip it if you are doing primarily breadboard work. Of course having a pot of liquid solder lying around is also something of a safety hazard.				$17.00
	Alligator to Alligator Prototyping Cables 50cm				$2.00/10pc
	Banana to Alligator Cable Pair Black & Red A set for every voltmeter, for the times when you need hands-free use.				$0.90
	50ML Epoxy Sealant Applicator Gun 1:1 and 2:1 There are a few different variants on the market and you have to match up all the parts of the system with your brand. This one works with Loctite.				$10.00
	Loctite Hysol 30-CL, Clr, 50mL, Cartridge This stuff has proven to be a good potting compound after more than a year of marine water exposure at depth. Takes >24 hours to cure. Alternatively, you could pot with a neutral curing silicone like RTV 128. but be careful with silicone as many emit circuit-wrecking acetic acid while they cure (so if they smell like vinegar – do not use them!)  MAS marine epoxy is a much cheaper alternative option for larger jobs, if you don’t mind mixing it yourself, and using syringes to apply it to the circuit boards.				$11.40
	Static Mixer Nozzle BT MA6.3-21-s Don’t use the shorter nozzles with less than 20 elements, or the epoxy does not mix &  set properly.				$21/50pc
	Scotch Permanent Mounting Tape, 1 x 450 Inches 5LB This stuff is immensely useful when you are putting a prototype together, and you just need to mount your boards inside a housing. Always have a roll on hand.				$15.00
	Deluxe Label Maker A label maker is a vital piece of lab equipment. I go through 4-6 ribbons on my old old Brother P-touch setting up for each class. Not sure which one to recommend from the current crop, so you have to do your own homework there. But just get one.				$25.00
	Multi-tip Precision Screwdriver Set Get one with at least 30 bits. And it never hurts to have a few of the $1/6pc sets around as well. If you are not budget limited, get the ones with the longer extension rod.				$4.50/32pc
	MG Silicone Conformal Coating : 422 The best way to protect Arduino boards & RTC modules from moisture in the field. Clean the boards thoroughly with 90% isopropyl alcohol first, and apply the conformal in a fume hood, as this stuff is really nasty. In a pinch you can also use clear nail polish as a protective coating instead. Avoid bathroom silicone rubbers for potting electronics, as they off-gas vinegar during curing which destroys electronic circuits.  And if your students are putting their loggers into the wild, throwing in a couple of silica gel packets into the case will protect from excessive moisture. Get the ones with color indicator beads, so you know if they are still working.  You can also re-use these packs if you dry them out with repeated short 10-15 sec intervals in the microwave, but the procedure takes a while to do properly because you have to let them cool down between zaps.				$15.50
	5″ Opening Pliers If you run into a situation where your heat shrink doesn’t quite fit over the item, these fix the situation.				$6.50
	WEN 4208 8-Inch 5 Speed Drill Press You can use a hack saw for most small cuts, but sooner or later someone is going to need holes in something, and this Sears knock off is cheaper than many hand drills. I also use a bench top band saw quite often, but table top scroll saws are probably safer for classroom situations though it’s nearly impossible to get a straight cut out of them. And if you are handy with the soldering iron,  you can often retrofit lithium batteries into portable hand tools after their original cells are shot. It’s also fairly  easy to remove the rust from any cheap tools you come across at a garage sale.				$70.00
	Extech EX330 Autoranging Multimeter Cheap multi-meters have a host of issues, like for example, not being able to measure meg-ohm size resistors because their internal resistance forms a parallel circuit with the resistor being measured.  So you need to invest in at least one better quality multimeter for your classroom. Though the EX330 is would still be considered “low-end” by professionals, it has served me well for years.				$48.00

Addendum 2016-09-15:

Finally have things set up for the next bunch of students, and since it’s unlikely to look this pretty again for a while, I though I would post photos of the classroom set ready to go:

It all fits comfortably into these two cabinets, but we could probably get that down to just one if we had to.

Addendum 2017-10-01:

Just found an interesting circuit visualization idea at instructables.  It’s a pretty time consuming method, but it’s easy to see how this would be applied in a classroom setting. One of the drawbacks of standard breadboard methods is everything on the underside of the boards is hidden once the pins are in place. You could do this with cheap pre-cut acrylic platforms.

Addendum 2017-10-15:

Codebender is an online Arduino IDE alternative that uses a javascript plugin to let your browser access your computers serial ports. The subscription is $10/month, and the .edu version of the service opens the possibility of collaborative projects with your students for an extra $0.50 per seat, perhaps even giving you the ability to grade/guide student work from any location without having to move a bunch of script files around. As an Arduino instructor, Codebender could save you 2-3 hours of computer setup just installing local IDE’s for a workshop. I’m a big fan of the default IDE, but given how much of a pain Github can be for Arduino-scale projects (especially if you work from multiple computers, or if your hard drive fails and you have to rebuild everything), this provides an interesting code-sharing alternative worth looking into. They also have more than 600 sensor libraries in their archive, and since library installation is always a stumbling block for people new to the Arduino platform, this could help beginners.

There are a few issues that are worth considering though: it only works in chrome or firefox, and everything internet related breaks eventually, and will continue to do so in the future, so you need a backup plan for any downtime or loss of the network. If you experiment with weird new Arduino compatible board variants, there’s a good chance those board definitions won’t be available in Codebender, and none of the libraries I use regularly were there because they were one-of variants that I found after digging through GitHub.

Addendum 2017-12-14:

Looks like I’m really late to the party, as Arduino has had its own web editor & cloud service for quite some time now. The Arduino Web Editor is supported on Windows, Linux, Mac and Chrome OS. The Chrome OS version is a buck a month, which is considerably cheaper than Codebender.  The thing about this that’s mysterious is that I work on the platform almost every day, scouring forums for code tricks, looking for cool sensors, etc.  –  and I’d never heard about it.  At least not in the forums & blogs.  Makes me wonder if the board discovery method that’s baked in to their service means that all the clone boards like moteinos, rockets, etc are not allowed to join the party(?) Fair enough I guess, since they need to make a little coin to keep something like that flying, but still curious…