Jimbo Harris was good enough to tell me about his USB modification of my digital setting circles project. Jim found the FTDI TTL232R and was able to adapt his DSC interface to communicate via (and draw power from) the USB port.
Jim wrote to me:
The TTL232 modification was a success; I connected to the board in place of the MAX232 at pins:
+5v – pin 16
GND – pin 15
Tx – pin 11
Rx – pin 12
(all corresponding pins of the MAX232), and I left out the MAX232, 7805, and all the corresponding caps, etc. The interface booted right up. I connected via both your program and also via the ASCOM driver (in ASCOM Validator and in DSLR Focus). I got the same results both ways.
Here’s the marked-up schematic that Jim sent me:
Jim also sent me a photo of the TTL232R kit:
And here’s a picture of his connection of the TTL232R to the interface board: