I have a custom PCB with an Atmega8 (or ATmega328P) which drives some small motors rated 0.5A. I program it thru a FTDI232, which I am also using for testing (send cmds via the monitor and get back debug print messages)..
How to I correctly connect simultaneously to both external bench power supply for the required power and to the FTDI232 for the debugging?
I've tried powering the PCB with my bench power, and only connecting RX/TX from the FTDI to the PCB and also a common ground. But power is going up through the FTDI and even into the USB. That can't be good.
** EDITED ** I've decided to piggy-back an RF isolator based on the SI8621BB-B-IS to the FTDI232 module. That should solve it.
That could be normal with your design. Are there a red and purple wires or green and white to the big motor? This is about as good as you will get as I am not clairvoyant and cannot see what you can. Post an annotated schematic showing all connections, power, ground, and all components include resistors etc. Where is the TTY part?
No one mentioned a big motor, or that it had wires attached to the terminals, or that it didn't work. (In fact, none of the above).
I have no idea why the FTDI232 module is acting so oddly, but I'm going to put an isolator on it and stop it. That should simplify things. Cheers.