Heltec LoRa 32 V2.1 Battery voltage reading

Soooo… whats the skinny.
I’ve searched here and on the net.
Lots of information and no one agrees.
The battery voltage readout and charge percentage.
Does it use GPIO37? as that is a GPS pin.
The displayed value bounces randomly between 3.6v and 5(ish) v.
Almost like it is trying to read a com line.
This happens whether connected to the USB cable or not.
Is this a bug or have I missed something basic?

yep, pin 37 is used for battery monitor.

Look in this post for solving the battery problem

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All the latest firmware, everything is new as of 10 days ago.
I wish it were only that simple. I have adjusted the multiplier from 1.7 to 10.
2.91 gave me good readings for six or seven screen updates.
Then it’s wandering all over the place again. If it were constant it would be easy.
It also never seems to charge the battery all the way.(may be different problem)
3000mah Lipo, max charge rate w/ 2A charger, 6 hours, still only 4.1v. I have a USB power analyzer coming.
The thing that I can’t settle the the stability of the readings. +/- 0.05v I can understand. +/- 0.80v I can’t.
But…GPIO37 is a com line for the GPS…How does that work??
Yes I went thru the solar post. No it didn’t cover the problem I’m seeing…exactly enough.

The charge current on a heltec 2.1 board is limitid to about 100 mA , so it can take a while before your Lipo is fully charged.
If you dare you can change R9 which is 10kohm on the prog-pin. The charge current is 1000 times the current through R9 while there is about 1V on pin Prog of the TP4054, good luck with that :innocent:

Also the instability you describe looks like a hardware issue and is not an meshtastic issue.
As there is no GPS module attached, there is no problem in using gpio37

You can add a line in the heltec variant.h source code and recompile
#undef GPS_RX_PIN
#undef GPS_TX_PIN
to see if it makes any difference

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Well…grumble. So Heltec doesn’t have the programmable charge current?
Will have to try without the GPS connected and Module installed.
Also if I’m going to compile a custom firmware I will move the GPS pin one I/O, GPIO38 looks free.
Really wanted to use “out of the box”.

Reflashed without any GPS and removed the connections. Things are behaving rather well.
Conclusion: Can’t use GPS and battery monitor at the same time ??..!

Great that you finally resolved the issue… The reason why you had the issue is the fact that the GPS module will send values through the RX/TX (GPIO37) of the heltec lora32 v2.1 (which will obviously increase the ADC values as and when there is GPS reading). Hence the values will toggle or the RX/TX of the GPS (connected to GPIO37) reading will take precedence over the LiPo readings.