I'm always excited to get emails from readers of the blog. It makes me feel good when I know that I've shared knowledge with someone. Especially someone I've never met. That's the case this evening, I received a comment from Andre asking for a circuit diagram of the AC Serial Switch. Not to disappoint, I opened mspaint and doodled a quick diagram.. I tried to make the diagram as true to life as possible.

On the Solid State Relay, each contact is labeled. Contacts 1 and 2 are for completing the AC's circuit. Contacts 3 and 4 are for controlling the completion of the circuit between 1 and 2. Contacts 3 and 4 on this particular relay "support" between 3 and 30VDC. Contacts 3 and 4 are tied to the DTR and GND of the serial port, respectively. The +12VDC that the serial port supplies is more than sufficient to switch the relay.

You'll notice that the AC is grounded to the relay's mounting point. The solid state relay has a heatsink on the back of it, that the ground is secured to.

Jim Vaught and I were extra paranoid, and put a 120V switch and 15A Fuse inline before the current ever got to the relay. Furthermore this is switching the black (hot) wire, that way there is no live current when the switch is open.