Protoboard
Since the DC motor is powered by +12V from a separate power supply, and the rest of the circuit is powered from USB, the prototype board is divided into two separate sections, 5V and 12V. To play safe, the two sections are completely isolated by optocouplers. The DC motor controller is a basic H-bridge with TIP29A and TIP32C power transistors as drivers (similar to this design, but modified to use components I had at home). The additional three wires to the motor/pot assembly are for the potentiometer value, ground and voltage reference. These are connected to the A/D converter of the AVR. The USB, finally, uses the USBtiny software implementation of the USB protocol.
Exposure Time: 1 sec • F-Number: f/8.0 • ISO Speed Rating: 100 • Focal Length: 12.30 mm