This is a very perplexing problem - hope somebody will have an idea.
This is a mature project that was working. It has an A-Star 32U4 board, a CP2104 usb-serial input and some stepper driver board to run 4 steppers. It is intended to run ‘standalone’ as part of a museum display.
All voltages and connections on the board have been check - and the board has run stand-alone in the past. Recently after connecting a PC and uploading a new version of the sketch - it will no longer run when the USB connection is removed from the 32U4. When connected - it works 100% as programmed. As soon as it is disconnected from the USB port it stops.
The CP2104 also has a micro USB connector and it’s outer metal shell shows continuity to ground. The outer metal shell on the USB connector of the 32U4 does NOT connect to board ground. Should it?
In standalone - the board is powered from a Meanwell dual voltage power supply - 5V & 12V for the steppers.
Please note as you review this: The board works 100% correctly when plugged into a USB tied to a PC. This would seem to indicate the board has no major wiring errors. Baud rates are all correct (57600). When operating, serial data coming and going from the 32U4’s serial pins at 0&1.
Is there any special setups needed to the 32U4 board itself that could cause such an odd situation?
Regards = Alan R.