Relay interface
If you don't mind a little soldering you can build this simple but reliable circuit to connect 5V relay boards to your Raspberry Pi. This works with SIP without any software modifications.
There are only a few inexpensive conponents needed:
- 74HC595 Shift Registers
- a few pin headers
- some jumper wires
- a 0.1 microfarad capacitor
- a bread board, perf board or other support
you can get them from most electronics parts suppliers. for example Adafruit sells a 3 pack of 74HC595 chips for $2.75.
The diagram below shows a breadboard layout that supports up to 24 stations.
Each 74HC595 shift register allows you to connect 8 relays. You can chain as many shift registers together as needed.
If you will be using a large number of stations, especially if more that a couple of relays will be on at the same time, you should consider adding a separate power supply to run the relays.