CubeCell HTCC-AB02A battery connection question

#1

In my previous post ( Topic: CubeCell 1/2AA battery problem
CubeCell 1/2AA battery problem), I discovered that the built-in 1/2AA battery socket for HTCC-AB02A can not supply sufficient transient current for the LoRa radio to work properly from a typical lithium chloride 1/2AA battery. If I connect a standard Lithium polymer battery to the battery terminal, then it worked okay.

Heltec does not provide the detailed wiring of power management section of CubeCell board. It is not clear how the battery is connected. The function getBatteryVoltage() from example code also does not seem to provide correct battery voltage.

When I measure the [+] battery terminal, it is connected to the Vdd on the board. The [-] battery terminal is not connected to the GND signal. This seems to be very unusual.

Is there anyway that we can get hold of the detailed schematics of the power management section of CubeCell 1/2AA board? This can help to understand how to wire a Li-Ion battery correctly for this board.

#2

In the absence of any detail on the CubeCell charging circuitry, you might get some idea about what’s going on from the ESP32 board schematics:

The GND signal issue that you describe, depending on whether you are referring to the AA battery connection or the ‘regular’ JST connector, may be related to the way that the battery charging system is configured. While the ESP32 boards do not appear to include overcharge protection circuitry, independent TP4056 battery management modules that include battery protection circuitry isolate the battery’s negative terminal. In the absence of specific details from Heltec, however, we can’t know for sure whether or not this might apply in the case of the CubeCell boards.

Either way, I’m not sure that this applies to the AA batteries on the AB02A board, which the documentation indicates cannot be charged through the battery management system, suggesting that you may well need more detail from Heltec to understand what is going on there.

#3

Thanks for the schematics. The AB02A board does not have a JST connector, only the 1/2AA socket with [+] and [-] contacts. I connect a TP4056 to charge the Li-Ion battery and connect the Li-Ion battery terminal to the [+] and [-] contact of the 1/2AA socket. This arrangement seems to work okay even though the [-] terminal is not tied to the GND of the MCU board.

The remaining issue is the example battery voltage measurement function: getBatteryVoltage(). It does not seem to return correct battery voltage readings. It started at 3.9V then drops to 3.2V very quickly.

I used this function for a different CubeCell board (HTCC_AB02). It worked fine.

I compared the schematics of AB02 board against AB02A board.

In the AB02 board, the VBAT_ADC_Ctl signal connects to the G1 of the PMOS switch AO7801 which in turn connects ADC IN1 to VBAT. This is correct.

In the AB02A board, the VBAT_ADC_Ctl signal connect to the same G1 of the PMOS switch AO7801. However, the PMOS switch connect ADC IN1 to Vdd. This does not seem right.

I wish Heletc can provide the schematics to show how the 1/2AA battery is connected to the rest of the AB02A MCU board. This will allow us to figure out a good way to measure the battery voltage correctly.