I got this McDonald's toy monster (see last photo) and when you hit it or dropped it, it made the sound of breaking glass. Inside was a small plastic box containing a PCB with a black blob and a resistor, 3 batteries, a small speaker and a trigger switch made out of a very tiny spring. I pretty much instantly thought about using one of those red metal "In case of an emergency, Break glass!" boxes used for fire alarms, but even if I could get one it probably would be pretty expensive. So I started thinking about how to make something similar myself and searched the internet for pictures. In the mean time I had told my dad about my idea and a of couple of days later he somehow got me one of those original boxes. Ok, It's yellow not red but I love it! It's made of plastic so no short circuits and it made it very easy to drill the holes, there's lots of space so I could easily put a 9V battery inside, it has a 5mm red LED, and best of all it has a plastic protective cover.

There was a big round hole in the bottom which I covered with a piece of metal mesh and I glued the speaker on top of that. The glass plate (which has a transparent sticker on the outside with the printing) could move just about 1 millimeter up/down. I made a square hole in the black plastic base and glued a small print switch in it so it would just touch the glass. It works perfectly and the switch is strong enough to push the glass back up. I also added 2 bright white LED's underneath the glass, pitch control, a on/off switch, an audio output connector and an external trigger input.

No schematic but here's some additional information:
  • I used a 78L05 to get 5V from the 9V battery.
  • I replaced the original resistor on the PCB with a potentiometer and a small resistor for pitch control.
  • The audio output is connected to the speaker by a resistor and a capacitor.
  • The white LED's are connected to the speaker by a resistor.
  • The external trigger input is made using a CNY17 optocoupler.


audio samples: N.A.