Raspberry is becoming some sort of standard Linux hardware among hobbyists. The only thing that is missing here – is analog input. Since there is digitals pin available, the only way is to attach external board with analog interface. Ken designed a solution to this problem. He took MCP3008 ADC with SPI interface. This doesn’t take much of digital pins and gives 8 analog channels.
His PCB layout allows to connect multiple boards in to chain and this extend number of channels. Two boars – 16 channels and so on. Circuit board was designed using circuits.io – web based interface. This makes process really easy from start to the end.