Check out this video on the result:
The object of the game is to cut the correct wires to stop the clock in time. During the day they got several coded messages on some of the colour codes used on the wires (but not all and some confusing). Cutting one of the four correct wires results in one of the red LEDS switching off and one off the green switching on. Cutting a wrong wire switches on an orange LED. Reaching four green LEDs switches of the clock and switches on a voice recorder to play. For some scare the recorded message warns an explosion to be imminent, followed by a counting down fading as the bomb switches of completely with only seconds to spare ;-)
When four orange LEDs would be switched on ................ well nothing happens actually. After all the kids were supposed to win. Actually they cut only one wrong wire and the orange LED happened to malfunction (loose connection), but that did not diminish the fun.
I made this for a one time use and kept things as simple as I could. I also kept this Instructable very simple, just the parts list, an explanation on the circuit diagram on the building. If you have some basic knowledge of electronics, it should set you on your way if you wish to make your own version. If you have some serious knowledge of electronics, you can probably improve it significantly.
This also an entry in Kiteman's "International-Go-Pro-Challenge". Check it out!
Step 1: The parts
A 12V battery
4 red LEDs
4 green LEDs
4 orange LEDs
Two 1 kOhm resistorsA 2.5 kOhm trimpot
A 12V relay with single or double SPDT switches (double makes adding an optional blinking indicator LED easy)
A 2N2222A transistor or any NPN general purpose switching transistor capable of driving your relay
Some colour coded single stranded wire, at least 8 pieces of 20 cm length (to be cut). A piece of ethernet cable is a good source.
A breadboard or some other way to build the circuit and some more wires to make connections.
Some wires with alligator clips to connect the clock, its battery and the optional voice recorder
Some tape to attach or mask parts
A voice recorder that plays back when switched on. I used a small sound recording module used for greeting cards product ID 191184 at Conrad
A blue blinking LED And a another 1kOhm resistor
Something to put everything on or in. I used a case with a board cut to fit and to hold the 12 V battery