This is a receive and transmit OPTO sensor for pinball machines. It is designed to be used in a switch matrix. The Transmitter board is just a simple resistor and IR LED that accepts 5V. The Receiver board has some magic on it that allows it to draw power from the switch matrix and hooks up just like a switch would in the matrix.
The boards sizes are 1.125″ x .5″. Even included handy mounting points for installing them into pinball machines
PCB Files (Eagle V6)