It’s a pressure plate used on halloween to make lights go on and off. Like this

This year I wanted to spice up the pumpkin booth with something interactive. Step on the board, make some lights happen, step off, back to where it was. Surprisingly I actually made it, even more surprisingly it lasted a few hundred kids stepping on it. At the end I’ll go through what went right and should be improved.

I had some plywood left over from something or over, enough for two boards of about 2’ by 5’. In retrospect, using some wood that had been lying around for a few years was a mistake. As you can see in the picture it was a bit warped, which is going to cause some issues later.

The two pieces of plywood need to be kept separated when they are placed together, so I glued a plywood strip about 1/4” around the edge of one piece.

To make the boards into a giant switch, I taped down some kitchen foil (with the shiny side up, no idea if that makes a difference) on each piece. The extra piece at the ends is so I have some where to attach a wire.

For each piece I soldered a piece of wire to the foil and used electrical tape to fix in place. Soldering the wire to the foil took a few goes and I wasn’t convinced I had a good connection until I tested it.

Now the two pieces were put together and screwed down. At this point it was clear the warped wood was going to be an issue. The two pieces did not lie flat on the floor, they rocked. But the proof is in the pudding so I wired it up to check.

I had brought a Spark Fun IoT Relay for this job. According to peoples on the internet, buying a cheap relay module and wiring it up is easy peasy, but I just wasn’t sure of my ability to safely work with mains voltage in outdoor setting. The Spark Fun relay was a bit pricey but was a sealed unit and rated for outdoor use. The relay works like a power switch, only the input is an electrical charge. Apply a small charge to the input and the relay opens. In my case, step on the pressure plate to complete a circuit powered by some AA batteries and turn on some spotlights.

The relay and batteries for the circuit are in the plastic case. I turned everything and immediately the relay tripped and the spotlight turned on. The boards were touching without being stepped on. Over the next hour or so I tried combinations of loosening the screws holding the boards together, adding more height between the boards to separate them and finally some cardboard separators.

The picture shows 3 strips, I think I finally ended with 2. But it worked! And it was incredibly satisfying to step on the wood and watch a light go on. Many, many times.

Here’s the pressure plate in front of a table with pumpkins on. The Spark Fun relay does some interesting things, so I had a strip of lights on when the pressure plate is not pressed, then when it is pressed those lights go off and the spotlights go on. Go watch the video at the top of the page to see it in action.

In case you are wondering why go to all this effort for a couple of kids, you should know our house in on some kind of Trick or Treat Nexus and we easily got 300+ kids this year.

Conclusion

On the plus side, the pressure plate survived a cool Fall evening (around 4°C) and two hours of being constantly stepped on. Lights on, lights off, over and over again. But on the down side, it was thick enough that some kids tripped over it and worst of all, only two people mentioned the lights! They were so focused on the candy they didn’t notice relatively subtle light changes.

Notes

  • sound effects would be noticed more, especially loud, short ones
  • the pressure plate was too close to where the candy was. If they were further down the drive then any affect would be more noticeable. But then the pressure plate would need to be less obvious.
  • the pressure plate needs to be thinner, and preferably more flexible. I'm wondering about using fabric.