Picture of Flashlight Tag Light Sensitive Badges
flashlight tag-test.png

Flashlight tag is a beloved kid's game, and I always love to throw a new spin on an old classic. So just for fun, I decided to add electronics to the game and I designed some pin-on badges that beep whenever you shine light on them. This gives sort of a laser tag feel to the game, and also resolves any debates over whether a person has been tagged or not. Here's how to make it.
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Step 1: Materials

Picture of Materials

Printed circuit board (Radio Shack part #276-159)
Three 1.5V button cell batteries
555 timer IC (Radio Shack #276-1723)
CdS photoresistor
1μF capacitor (4.5V or higher)
3-12V piezo buzzer (Radio Shack #273-074)
1MΩ resistor
10KΩ resistor
Heat shrink tubing
Safety pin
Large paper clip
Switch (optional)
Jumper wires
Clear plastic sheet or case

Additional tools:
Heat gun
Hot glue gun
Soldering iron

Step 2: Circuit

Picture of Circuit
flashlight tag-batteryholder (3).png
Here is the circuit that I designed. It is a basic 555 timer circuit in monostable mode. In this configuration the IC sends one pulse to the buzzer every time pin 2 is brought low (below 1/3 the supply voltage). The length of that pulse is determined by the values of the resistor between pins 7 and 8 (in this case, the 1MΩ resistor) and the capacitor. Increasing the value of either of these components will increase the length of the pulse and reducing either value will shorten the pulse.

There are a wide variety of the CdS photoresistors and the manufacturing tolerances vary wildly. The one that I used had a range of 3KΩ when well lit to 30KΩ when dark. Depending on the photoresistor that you use, you may need to change the value of the resistor between pins 2 and 4 (the 10KΩ resistor). In order to activate the timer, this resistor must have a resistance at least two times larger than the photoresistor when it is illuminated. Adjusting the value of this resistor will also change how sensitive the sensor is. I recommend trying out several values before soldering the circuit together.
VoiVode3 years ago
Nice!! I wanna build some for me and my friends.

But i got i Question, is it possible that in your picture with the circuite, you made a mistake with the left resistor?? There is a 1k resistor, but in your To-buy-List you wrote 10k resistor??

I try your Plan with an Simulator and its only work with a 10k Resistor....
DIY Hacks and How Tos (author)  VoiVode3 years ago
The 10k resistor is correct. I will fix the schematics as soon as I get a chance.