This is a very niche question but I'm wondering if there is a general princinal that can be applied to help answer it.
Here is my prediciment. I am making an Arduino on a breadboard. For the power supply, I am using this Breadboard Power Supply Stick. For the USB to serial I am using Board for RL USB to Serial. I have got everything working, sort of.
The issue is, that when the breadboard power supply is at all attached to the board, even if it is not plugged in, it makes the USB to serial connection unable to upload programs to the ATMEGA328P. If the power supply is switched off and even unplugged from the wall, the USB to serial connection does not work. The only way that the USB to serial connection works is if the power supply is physically removed from the board.
Why is this? How can I fix it? Ideally, what I would like to do is be able to power the mC and a few servos using the breadboard power supply(the USB alone can't power much), while still being able to program and read serial out from the chip on my computer while the program is running.
Here is the schematic for the USB to serial connection http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/FT232R-Breakout-v36.pdf
Here is the underside of the USB to serial board http://arduino.cc/en/uploads/Main/arduinobb_usbback.jpg
Here is the schematic for the bread board power supply http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/Breadboard%20Power%20Supply%20-%20SMD%20v13.pdf