You can find 5VDC on:
1) Pin 1 of your game port (DB17 connector)
2) The red wire in a decapitated PS2 mouse cable
3) Any USB port
Connect a 220 Ohm resistor +5VDC, connect the opto-LED anode to the other end of the 220 Ohm resistor. Take the opto-LED cathode to the parallel port output pin of your choice.
Caveat: Many / most new PC parallel port outputs are 3.3V logic now. Toggle the port output pin, set a multimeter to DC Volts and measure the pin voltage. If you do not read at least 4V for a logic '1' ouput, you have a cursed 3.3V port.
If so, then do the following:
Connect a 470 Ohm resistor to the 220 Ohm / LED anode junction. Take the other end of the 470 Ohm resistor to parallel port ground. Then it will work with 3.3V logic as well as 5V logic.
Mariss |