This little device is a fun tool for pranking your friends and coworkers. Every few minutes it emits a brief, high-pitched beep. The beeping gets annoying after awhile, but what is really frustrating is not being able to find it. If you choose a good hiding spot, it can take hours to figure out where it is.
Step 1: Materials
3 Button cell Batteries (I used LR932 cells but other sizes will work)
Printed Circuit Board (RadioShack #276-159)
3-16V Piezo Buzzer (RadioShack #273-074)
100μF 10V Capacitor
555 Timer IC (RadioShack #276-1723)
The values of the capacitor and resistors are not critical. You can easily replace them with capacitors and resistors of similar values. The only effect will be that it changes the time between beeps. See Step 2 for a better explanation.
The PCB can also be replaced with any other PCB with enough holes to fit all the components.
Step 2: Circuit
The circuit is a basic 555 timer circuit in astable mode. In this configuration the IC sends a brief pulse to the buzzer every few minutes. The values of the resistors and the capacitor determine how often the buzzer will sound and how long each pulse will be. Increasing the value of either the capacitor or the resistor between pins 7 and 8 will increase the amount of time between beeps. Increasing the value of the resistor between pins 6 and 7 will increase the length of each beep. Decreasing these values will have the opposite effect. With the values that I used, it beeps about every 6-7 minutes. (If the capacitor is completely discharged, the first beep may take up to twice as long.)
Step 3: Battery Connector Pins
The only parts that you need to make are the battery connector pins. To make these, cut off two pieces of the paper clip that are about an inch long and fold each of them in half. The bent end is where they will contact with the battery. The cut ends will be soldered to the board.
Step 4: Assembly
Then solder all the components onto the board. If you are using the same PCB, you can just copy my layout. If not, just make sure to follow the schematic on Step 2 and check all the pin connections. When soldering the battery connector pins, try to align them so that they are leaning slightly towards each other. This will help make a tight connection with the batteries.
Step 5: Trim the Circuit Board
After soldering everything together, I trimmed off the unused part off the circuit board to make it easier to hide. I used wire cutters to remove the large chunks and a dremmel to trim up to the edge of the circuit. In hindsight, it would probably be a lot easier to cut the board to the needed dimensions before soldering all the parts onto the board. So if you know where all your parts will be, I recommend trying that.
Step 6: Finished Product
Then just insert the batteries and your annoying beeping prank is ready. Now all you have to do is find a good hiding spot. You can put it inside someone’s computer, tape it to the inside of a drawer, or stick it behind a piece of furniture. Use your imagination. The batteries should last between several hours to several days depending on the size of the battery that you used. But your victim will probably find it before the battery dies depending on how determined/obsessive they are.
Be creative and have fun.