The Atmel ATMega8 (U1) controls the whole circuit and interfaces to the Robo TX controller. U2 and U3 are used to drive the 8 outputs. Every output is protected using a self-resetting polymer fuse. The 8 inputs are protected using zener diodes and a current limiting resistor. The power supply is protected from wrong polarity connection by a diode rectifier.

 

 

The PCB is populated on both sides. All the connectors (I²C and banana plugs) and some other components are mounted on the bottom side of the PCB. The pictures below show the populated board's top- and bottom side. 

Use sockets for all integrated circuits to allow easy changing.

The 2mm banana plugs are mounted onto the BCB using a piece of 1mm diameter wire that is first screwed into the connector. Then the whole connector is mounted onto the PCB.