Introducing Boxy

Watch this video on YouTube.

Here’s the up-to 15 amp wall socket switch I’ve been working on, dubbed “boxy”. With a big enough heatsink you can use it for 15 amps and with no heat sink 5 amps may be too much. My primary use for this contraption is going to be for “sous vide”, a cooking method based on tightly controlled temperature. And for this the boxy will be switching a 1100 watt countertop hotplate, and that means about 10 amps. I’ll need a heatsink, but a moderate sized one should do.

Note that only the 2 yellow jumper wires closest to the battery are doing anything (and this demonstration would have worked with only one of those). All the other wires are just left overs from previous tinkers.

Now for the features of the boxy:

  • Completely isolated (from mains voltage) control circuitry accessed through 4 wires exiting the boxy
  • internal (and also isolated) zero cross detector – pulses every zero cross (120Hz for home sockets in the US)
  • simple control on one pin, drive it high to switch on, drive low to switch off
  • common ground for the zero cross

In the video I have the control wires exposed by a regular 4-wire phone cable and connector, though you could use whatever 4 pin connecter is most convenient for you (like a TRRS, RJ45, screw terminals, molex, etc)

Made from:

  • 1x Steel handy/utility box, $0.91 at Lowes
  • 1x 1 ft extension cord (sometimes called “Power Strip Savers”) cut in half, $8.50/5 on amazon
  • 2x NM cable connector (plastic: 20 cents each in a 10 pack, adjustible steel: $0.40 each)
  • 1x Cover for the steel box (in the video I have an aluminum plate which helps for heat dissipation, I have no source for these, though you could cut/fab your own), Lowes has a cover with a punch out hole (useful for the heatsink) for $0.98
  • 1x heatsink, necessary for any appreciable currents (lights would be fine without)
  • PCB and electronic components (to be included with the build instructions) ~$5-$10?

When I post the build instructions I’ll have a tighter cost estimate (and probably even kits for sale), but I think this could be built for under $20 apiece. Stay tuned for the build post!