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It's possible the battery was low for the self test, because for this type of bench check I tend to use any old battery laying on my desk. But in the field I try to use fresh batteries, and I actually find E.getBattery to be too coarse of a measurement to monitor their condition. If I use them to the point E.getBattery reads anything below 100% I start seeing power failures. I think this is due to the full power advertising I'm doing. And the field measurements are sometimes taking place in a very cold environment, which doesn't help battery capacity.
I instead run NRF.getBattery each time I program them for a mission, and I strongly consider replacing batteries if it reads less than 3 V. At this point (and well below it) E.getBattery still reads 100.
Also, I only saw the LED message when the resistor was still connected from D28 to D30. When I cut it that went away, but I still had both D30 and D31 errors. Yesterday I tested several other failed pucks and got similar D30/31 errors. Can you point me to the code the self test runs?
I did the test without anything connected and with the resistor still connected. When it was still connected, it looked pretty much the same but it also said:
"LED2 pullup voltage out of range (0.542...) - disconnected?"
and error code was LD2, not L30
The LED still worked when I set it high.
Looks like the self-test backs this up too. Interestingly though it looks like D30/D31 may have ended up partially connected together as it seems like if D31 is floating, D30 can still read a value?
I'm not sure exactly what you mean here. D30 reads ~0, but with everything disconnected I'd expect that. Do you mean for me to try this on a board that hasn't been desoldered?
The circuit is as you described. For future versions I will put one side on ground. As far as water/sweat damage, I can't rule it out but it seems unlikely. I will try to get a picture of one of the setups posted.
The UART issue seems unlikely to me because the Pucks typically run for hours without problem beforehand.
The pucks are not grounded in any way, run from a CR2032, and the thermistor is actually the SR version (so no washer, it's a disc but with no hole) and is taped to a finger or toe. There are 2 wires leaving the puck, attached internally to a 2-way connector screwed onto the puck body. The thermistor connector mates with this.
I did the self test on a bad one, and got:
Pin D30 shorted low
Pin D31 forced low
Pin D31 shorted low
Error code L30
I'm guessing this isn't good.
It would be difficult but not impossible to touch the bare wires. If the connector was partially removed it could be done. But a couple reset today that were happily chunking along with no indication of a problem. This time I was able to read the thermistors fine after reprogramming.
I have attached the code. Thanks for the help.
I am using several (~35) puck lites to collect temperature data via external thermistors wired to pins 28, 30, and 31 following a similar procedure to your thermistor write up. I'm also advertising the data for live view capability. The thermistors are monitoring human skin temperature. Mostly they work fine and seem to be quite accurate.
The problem is, every day I use them I am losing about 2-3 pucks. They start reading bad temperatures, usually 5-10 deg. F higher than they should be, but sometimes 60 or more degrees off (which is a lot easier to spot!). When I disconnect the thermistor and check with a multimeter they frequently have low to very low impedance between pins 30 and 31 (the middle of the voltage divider and the low signal), but not always. I have not been successful in getting them to work again, at least without changing the circuit layout, and end up changing out the boards completely.
Another problem I see less frequently is the puck will completely crash for no apparent reason (it's more than a software reset - it loses its NRF advertising settings too). It's as if the battery died but it happens on fresh batteries and only an hour or so into logging/advertising. Often this will result in the bad measurements as above when I try to refresh them.
My best guess is static discharge is frying my boards but I'm really at a loss. Should I be using a capacitor to protect the ADC pin?
I'm using SR type probes from here: http://thermx.com/temperature_sensor_selection/Thermistor_Probes.htm
Thanks for any insight!
Hi Gordon, I haven't been needing to use these for the past week or so, so I haven't made the code change. I could do a handful of them and let them chunk away, but I don't have time to deal with all 35 of them at the moment. Do you think that would be worthwhile?