@Rongzhong Li Thank you, Nybble is now partially alive. All optimizations as mentioned in post Root cause analyse on strange FTDI232 / NyBoard behavi our and finally correct type of batterie really helped a lot. Calibration was now working and Nybble became partially alive. Now there is only one strange behaviour left which is hard to describe. I installed Nybble.ino and I could perform most commands via IR. But for example in BALANCE mode I detect the board making a beep noise and movement partially interupts, but within a second calibrates back to correct position. Or in WALK mode the movement is interupted almost every second with a short stop and beep (as cat needs to have a short rest). Any idea why this happens.