Heltec V2 Battery

[t-huyeng]

Hey,

I have some Heltec LoRa V2 boards which I am using.

I have also enabled battery mode, but am not sure if I have done something wrong.
I am using the halfile = heltecv21.h, the battery values start at about 2600 [?] and go down. So I think the board is measuring something. But I cannot translate it to a voltage. Is my decoder old or faulty?

Has anyone had the same problem with Heltec boards?

Thanks

[cyberman54]

Heltec has simple battery monitoring by using a voltage divider at GPIO pin. The ratio R1/R2 is setup in heltecv2.h, please check the resistor ohm values. Maybe Heltec changed it on the board, or ratio value in hal file is wrong.

[t-huyeng]

Good tip!

I will try to find the resistors on the board and check them.
A quick look at the schematics shows 220/100 as it is currently in the hal file. https://github.com/Heltec-Aaron-Lee/WiFi_Kit_series/blob/master/SchematicDiagram/WiFi_LoRa_32(V2)/WIFI_LoRa_32_V2(868-915).PDF (5 years old)

This schematics are up to date with PIN 37 https://resource.heltec.cn/download/WiFi_LoRa_32/V2.1/WIFI_LoRa_32_V2.1(868-915).PDF

But it looks more like it needs #define BAT_VOLTAGE_DIVIDER 3.2 to calculate correctly, so the resistors are more like 320/100 I think.

[cyberman54]

Note GPIO21 om Heltec v2.1 ("Vext" Switch): It is necessary to switch Vext on, before measuring battery voltage. Otherwise the voltage divider is not powered. This is coded here, should work, but maybe to be re-tested.

[t-huyeng]

With the tools I have I am currently not able to check the resistors on the board. But I will try to find a way to check them . As described #define BAT_VOLTAGE_DIVIDER 3.2 works as a quick fix for me at the moment. But I will also try to check if Vext is switched on.