Gadget Freak Case #272: Motion Sensor Light Switch

Are there light switches in your home that aren't as conveniently located as you would like? This laser-based switch decoder and driver allows for flexible control of those lights located in less than ideal places.

I live in an apartment. My kitchen is boring and can be accessed from either end of a central counter. This laser based control, mounts just below the cabinets, scans across the entire sink's counter surface using a single beam of a modified laser pointer. The interrupter beam is detected, processed to provide multiple possible hand based gestures, and the result drives a small relay that enables and disables the light fixture directly over the sink. Sure makes getting a drink of water a bit more interesting.

There are three assemblies in this project. Fashioned out of pill containers and a modified surge protector assembly, they include a wall mounted reflecting mirror, an enclosure with the laser, photo resistor, an indicator LED, an assembly providing AC based power, controller, and relay hardware.

The laser is only modified to minimize its physical length. I used an inexpensive laser pointer and cut the body down past its battery enclosure to just above the pointer switch.

Download the full build instructions here.

Download the compiled Hex file here.

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As always, Gadget Freak is brought to you by Allied Electronics and Design News. You can recreate William Grill's gadget using the Allied parts list below.

Parts List

Amount Part Description Allied Part # Notes
1 Photo Resistor - Dark resistance between 10K and 50K ohms
1 Laser Pointer - See text
1 Green LED 70061509
1 78L05 Semiconductor
2 4.7K ohm 1/4W Resistor
1 2.2K ohm 1/4W
1 330 ohm 1/4W
2 2N3904 NPN Transistor 70055539 Any small signal transistor with gain >120
2 1N4148 Diode
2 1N4002 Diode
1 220 ohm 1/4W Resistor
as needed 4 x 5 - inch Protoboard 70012455 Or equivalent, 0.1 centers PTH, clad on both sides
as needed Assorted 26/30 gauge wire -
1 500 Trim Pot (optional) 70154053
1 Power Cube - Equivalent with >.2A at 7.5V and < 18volts
1 Relay 70199164 This is specified as a 5V coil /w 250V,3A contacts
2 33uF 35V Capacitor
70255920 >10uF, with voltage rating appropriate for your app
as needed Assembly Containers - See text
1 12F675 Microcontroller
70045476 DIP specified but alternate packages available

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