these boards and schematics correspond to Alice and Bob's shields, which are circuit extensions of the arduino processing units. The peripherials that control the led pulses, clock signals and demultiplexing are all connected to these shields, as explained in the main body of the manuscript. Bob's shield include a data selector that is used with another communication scheme that is not described here, and in the described operation mode is set to connect the serial communication channels (Tx,Rx) directly.
