Can write but not read Mini Maestro 12 UART from RasPi


I have an application that controls the maestro from a PC through USB Dual Port using the virtual serial ports. Works fine.
Now I have ported this to a Raspberry Pi by using /dev/ttyAMA0 for both serial ports.
I can successfully control servo positions by writing to the serial port of the Pi but reading the serial port to get e.g. an input always returns nothing. (Empty buffer, not a zero value.)

Inbetween the RasPi and the maestro I have logic level shifters (Pololu #2595). I verified the correct voltages on the RasPi and maestro rx and tx pins. I configured the maestro to UART fixed baudrate 115200. And I disabled the serial console on the RasPi.

It behaves as if the maestro just doesn’t talk on its tx line. For example if I send a command the maestro doesn’t understand the red LED on the maestro lights up. If I then send GetErrors to the maestro the LED goes off but no bytes are received.

The application is written in Squeak (the engine under the hood of Scratch) so porting the application is as easy as copying the Squeak image file to the Pi and there changing both the command port and the TTL port to /dev/ttyAMA0.

Grateful for any hint.




measuring the voltages was not enough with all pins being held high by UARTs normally.

One of the m/f breadboard jumper wires was broken, so the maestro couldn’t pull the Pi’s RX line low.

Sorry for the noise, at least this can serve as an example for the error in front of the keyboard. :slight_smile:




I am glad everything is working now; thanks for letting us know what the issue was.