Review on Geekworm Full Function Motor HAT for Raspberry Pi 4B/3B+/3B - Robot Expansion Board for Raspberry Pi 4 Molde B, 3B+/3B/2B/B+ (Stepper/Motor/Servo/IR Remote) by Marianne Green

Great little board, the only one I've found for the Raspberry Pi that supports all three basic motor types - DC, stepper and servos . I wasn't sure what type I needed for my project so this helped me narrow it down. As far as stacking/addressing goes, it works like a charm (although there's no documentation). There are four solder points on the board labeled A0-A3 that control the address. Solder connects two small pins. They're soldered, so the address is 0x6f. Use an iron and solder wick to remove drips and you can get any address between 0x60 and 0x6f. Use the command "sudo i2cdetect -y 1" (without quotes) to show you the current address. For some reason you always see address 0x70 active on this HAT, but ignore it, you need an address from 0x60 to 0x6f. A few other notes/warnings: 1) Always turn off HAT power to the motor when messing around with the motor. Wiring, I burned one of the motor channels by briefly touching the HDMI connector housing wire. 2) DC/stepper motor drivers can work with AC voltage, but servos always use ONLY 5V. Using more will give you a little fireworks on both the board and your servos. 3) The stepper motor driver is limited by the I2C bus bandwidth (it has to send commands for each microstep), so I couldn't get them to move as fast as I know they can. I was able to slightly increase the baud rate on the I2C bus, but I started skipping steps. A smarter protocol might mitigate this, but for an entry-level experimental board, I won't lower it.