DeuceEFI wrote:Here is the PNP USB modification if you don't use the Opto-isolator circuits:
See the attached image...
The blue hand drawn line is to connect the MCU ground and the USB ground together, just use a piece of jumper wire soldered to the two pads of U8 and U9.
The yellow hand drawn lines show the connection points for the PNP transistor (I used a 2N3906 transistor). This is necessary to pull the RX line of the MCU high if the USB cable isn't plugged in.
PNP Transistor connections:
The Emitter goes to the +5v side of R60.
The Collector goes to the RX side of R60 or the RX pad of U8.
The Base goes to 5v-USB side of R56 (this is powered only when the USB cable is plugged in.)
I had did the hack with 2n3906. My prelim test shows the FTDI chip still not talk with the MCU.
Only the sending LED flash. will take time to check soldering and trace tomorrow.