Hidden in Light

This is a simple project i have made as a part of a treasure hunt that organized by our Computer Science teacher Mr. M. Vamvakaris and took place in the junior high school where i am working as a Science teacher.

There are 8 IR leds driven by a 74HC595 shift register. Pushing one of the buttons A or B or C the arduino sends a number to the shift register that it is translated in binary and the corresponding IR leds light up. The students see that pushing the buttons light up the red leds near the buttons but of course they cannot see the light from the IR.

We told them that something was hidden into the light and that the 8 leds were IR. They knew from the science lessons that they can "see" the IR transmission using a telephone camera (not a good quality one like iphone's that has a IR filter) so they managed to see the IR leds, calculated from binary to decimal, found the three numbers, sum them and unlocked a 3 digit number lock to get the clue.

What do you need

1x arduino or any compatible MCU

2x large breadboards

1x 74HC595 shift register

8x IR led

8x 1KΩ resistors for the IR leds

3x Red led

3x 560Ω resistors for the red leds

3x push buttons

3x 560Ω pull down resistors for the push buttons