Field Report 2016-03-27: Progress on the 1-Wire DS18B20 Temperature Strings

Happy to report the successful deployment of three more temperature strings:


and I think it’s fair to say the first two protoypes have almost run their course:

Logger/Sensors Time/Max.Depth Comment
#45  (19 x 25cm)
[1st build]
Full data from Temp chain, Qsil problem on pressure sensor
         (19 x 25cm) 201508-12
Wire break on 1st segment before deployment: total read failure on temps, pressure data OK
         (11 x 25cm) 201512-1603
Full record including pressure. Segment wire broke during retrieval. Brought home for refurb.
#46  (20 x 50cm)
[2nd build]
Full temp record. Pressure record problem.
         (20 x 50cm) 201508-12
Full temp record. Pressure OK after Qsil removed.
        (9 x 50cm) 201512-1603
3rd segment wire break during deployment dive. Nine sensors report OK for duration. Pressure OK. Failed segment removed & unit re-deployed.
#78  (24 x 100cm)
Complete data record. Unit redeployed.
#79  (24 x 25cm,  & 10m extension)
Wire break during deployment dive. Full logs saved but no data. Failed segment removed & unit re-deployed w 18 nodes
These internal wire failures did not compromise the integrity of the outer jacket.

Fortunately none of these internal wire failures compromised the integrity of the outer jacket. These are only 7-strand wires, and I will be hunting for more flexible 19 strand replacements.

While it’s hard to see all that work deliver only a few successful deployments, I’m happy to note the failures were all at physical pinch points in the cable, with no other apparent problems on the housings or electronics.  And even when the wires break, the logger itself keeps chugging along: saving logs full of 1360 & -1 read errors.  Sensor problems like this often take a whole logger down, but the MS5803’s delivered data through every deployment, so failures on the one wire bus seem to be isolated from the rest of the sensors on the logger.


Though it was always part of the plan, actually pulling off segment swaps in real time was pretty cool…

For existing builds, I reenforced the weak points with mastic tape

For the units in the field, I’ve re-enforced the weak points with mastic tape & cable ties to limit bending.

This is good news for me because physical problems are generally the easiest ones to fix…

Up to this point I’ve been using soft silicone jacket cable which is lovely to work with, but I will have to build the next set from sterner stuff.

Of course that means we might have to develop a new set of deployment procedures,  because handling 24m of stiff cable could be a challenge.  These deployments have already been some of the toughest dives on the project, especially when you get into the low-visibility hydrogen sulfide soup that Trish is so fond of…


The second generation builds also used less power than the first:

Much better power performance on the second generation of temp strings.

The battery curve is still a bit crunchy, but it looks like it might settle to about 100 mV drop per month at a 15 minute interval on 2x3AA’s.  That’s nearly the same as the first two loggers which had twice as many cells.  One of the things you notice about cheap DS18b20’s from ebay, is that they can draw dramatically different sleep currents.  This may be compounded by the fairly aggressive 2k2 pullup I use on the bus.


Spotted in Tulum:


Just finding a problem doesn’t always tell you how to fix it…

2 thoughts on “Field Report 2016-03-27: Progress on the 1-Wire DS18B20 Temperature Strings

  1. Sunny

    Not really sure what temperature strings here implies, but those battery curves and data logger do look good! Validation does seem to require a lot of effort. Great info there Ed Mallon.

    1. edmallon Post author

      During the first year of the project I was simply asking if it was possible to build Arduino based loggers that would work under water, and now I’m asking if we can produce research quality data from this DIY approach. But from the beginning, an underlying question has always been “How many tries does it take before I get this working…” and I had no information there because people rarely post about how things went wrong. People new to the makers movement need to see that because the mythic inventor hyperbole so often portrayed in popular culture hides the fact that perseverance is more important than brains…which is lucky for me. 🙂

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