Connecting a coin receptor to a key press
Things needed:


Cheap keyboard
Coin validator that can do pulse mode like this one
Low current relay, same voltage rating as the coin validator like this one
Power supply for the coin validator and relay
Multimeter , wires , soldering station and also some soldering skills


Read the coin acceptor data sheet carefully and make the connections to the power supply.

Use counter output schematic to connect the relay coil to the coin validator, read the relay data sheet because this one already has an internal diode. 

Dissasemble the keyboard and , using the multimeter, find the two pads on the control board connected to the key you need. If you cannot solder on them then take a different keyboard. Connect with wires the two pads to the relay contacts. To spare some space you can leave any other keyboard part and keep only the cable and the control board. 

See here a video of a disassembled keyboard where the control board has large pads to solder on.  

Power on all and, using the coin validator datasheet, set the press time to 100ms, counter/serial mode. 

Ready to use