Land, connect UAV to Configurator software and write down how much current our meter reported.Fly for about 30% of normal flight time you get from this battery.Take a fully charged battery, put it into UAV and go flying.In our case, procedure would look like this: It will not be super accurate, but accurate enough for amateur usage. Since most battery changers displays how much current were put into battery, we can use that value and calibrate APM Power Module. But, there is a simplified version that gives pretty good results too. Without quite expensive stand-alone current meter, proper calibration can not be done. Since ADC also has some internal resistance that interacts with the divider, I've discovered, that scale of 180 (for 220kOhm resistors) is the point of entry for further calibration. We have divided it by 2, so scale should be somewhere around 277. In theory, our meter provides 55.5mV/A, so the case should be 555. Default value of 400 will not work of course in our case. This is done via Scale the output voltage to milliamps setting.
There is one more step we have to take: calibrate the meter. Once APM Power Module is connected to flight controller, we have to enable and configure it. Bottom line, I've found out that 220kOhm does pretty good job. If you will use too small resistors, it would no longer be 1/2. In theory you can use any other resistance, but there is a catch: both INA169 and ADC input have some internal resistance that interacts with voltage divider. Two resistors and that's all! I've used 220kOhm resistors here. This is why, we have to scale analog 0-5V to 0-3.3V or less. While they might be 5V tolerant, analog inputs will not accept 5V!. Like I mentioned, this module outputs 5V when 90A is measured. When JST is used, then its lines are (from top to bottom like on a picture above): 5V, 5V, Current, Voltage, GND, GND.
In our case it is useless, so we can ignore it So, 12.6V on input will result in 6.3V on this pin. Voltage - this is input voltage divided by 2.This is a pin we have to connect to flight controller It is 0V when 0A goes through the module, and 5V when 90A goes through it. Current - voltage on this pin depends on current flow.5V - supplying 5V obviously, so it can be used as a BEC.Battery power leads, power leads for motors (module measures power going from battery to motors) and 4 THT pins: Pinout of APM Power Meter is pretty simple. You have to refer FC documentation and / or flight controller software documentation. Some boards have dedicated pins, on some boards PWM input pins are used for Current Meter ADC. I will not show where to connect APM Power Meter to flight controller, since this differs from board to board.
It's time fix the problem and finally present a short tutorial how to connect 90A APM Power Meter for flight controller boards like Naza32, SP Racing F3 or any other running Cleanflight / Betaflight / INAV software and equipped with Current Meter ADC input. This topic was eluding me for some time now.