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Beeping Motion Detector

beepingMotionDetector

We have this big box of candy at my office at work, that keeps getting more popular with people from the other offices. I wanted to make their sneaky candy stealing more detectable, with a beeping motion detector circuit.

Parts list

1kOhm resistor
4.7kOhm resistor
1.8 nF capacitor
0.01 uF capacitor
Buzzer
2x 9v battery
PIR Motion Sensor Module info
TLC555CP timer datasheet

Schematic

The 555 timer is set in astable mode, with the reset pin connected to the detector module output. It is quite a cool module actually, doesn’t require a big circuit to use it. The timer generates a ~5kHz pulse to the buzzer for approx 5 seconds when motion is detected. Here are the contents inside of the box:

I’ve taped everything a bit so that it won’t short circuit once crammed inside. The power connector is harvested from an old 9v battery, soldered on some wires and attached to the circuit. The other 9v battery from the parts list I used to power everything. I intended to power the circuit with a 3v coin battery, but the motion detector needed a minimum of 4.5v, and acted strangely with 3v. It’s a shame I don’t have a boost converter, but I guess this battery will last a lot longer.

I didn’t really do any fancy math or anything on this 555 timer circuit, as it is more about just getting a frequency to make a beeping sound. It just has to be within hearing range and whatever range the buzzer can reproduce. By the way, this is what it looked like on the breadboard:

And now, off to work to test it!

 

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