I just want to double check something on the PS2 cable for Roomba connection.
As I understand I need to connect to pin 3 (RXD input) and Pin 7 (ground) Your tutorials say to make sure there is no voltage or I will fry the D0 port.
So here is what I don't understand:
Pin 7 is supposed to be ground and when I connect the multimeter to pin 7 and pin 3 it shows no voltage. However, if I touch one lead of the voltmeter to the grounded base of the serial port (the outer barrel) and the other lead to pin three, I read 4.5 volts. Obviously there is voltage to pin three, but only when it is grounded to the port's barrel and not when I am connected to pin 7 as ground.
Also, pins 1 & 2 read between 12 and 14 volts when I connect the multimeter to those pins and the base of the port, yet when I connect the meter to pin 1 or 2 and the negative lead to pin seven, that voltage drops to 7.5 volts??
I suppose that I should just trust the meter that shows zero voltage when connected to pins 3 & 7, but What exactly is pin seven doing? Why does it show voltage when the multimeter is touching the grounded base and not when it is touching pin 7 ground?