Laser Switch Completed

I have finished my laser switch project (all related posts here).

The system works as follows: I have a laser pointer hacked into a duck hunt gun. When I pull the trigger on the gun, the laser points out from the barrel of the gun. On the wall, I have four picture frames, each with frosted glass in place of a picture. Inside each frame lives a photoresistor. This electronic component measures how much light it is receiving. When the laser hits the frosted glass, the entire box lights up and the photoresistor sees the spike in brightness. It then triggers a relay to switch on/off the lights in the room. Check out the previous posts for more technical details.

While it could be argued that the duck hunt gun could be omitted in place of a standard laser pointer or even a flashlight, it’s difficult to argue that firing a duck hunt gun for any reason won’t brighten your day.


I did end up making a modification to the circuit from robot room. The problem I experienced was that when the room was completely dark, one pair of lights would strobe on and off at a seizure-inducing rate. However, this only happened when the boxes were positioned a certain way. If I swapped the location of the boxes, the problem went away. Well, most of the time it went away. After some poking around with a multimeter, I noticed that when the room was completely dark, the photoresistors were peaking into tens of megaohms and were quite unstable. A change in the clock across the room would trigger a massive swing in resistance. So in theory, the circuit was working properly: when the resistance between the pair of the boxes was significant enough, the light would switch on. Then, I’m guessing, due to the position of the boxes in relation to the lights in the room, as the lights illuminated, the off switch would get triggered and the cycle would restart. To remedy this I added a 200K resistor in parallel with each of the photoresistors. This effectively places a gate on each of the boxes. In other words, there has to be enough light to bring the photoresistor above 200K Ohms before either switch can be triggered.

As this was my first project that connected low voltage (5VDC control circuit) to (relatively) high voltage (120 VAC mains), I spoke with an electrician about codes and regulations. My understanding is this: there is an imaginary barrier at 50V. Everything below 50V can live happily inside a box and everything above 50V can live together, but you cannot have a circuits on either side of the barrier cohabitating in the same box. Obviously if the high voltage/current were to come in contact with the low voltage/current wiring, the smoke would get out. Probably the flames too. Play safe kids.

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