Case #90: Ken Put an End to Expensive Front-End Damage

By: 
September 25, 2006

Not satisfied with the low-tech method of suspending a tennis ball from a string, Ken Swanstrom devised a better garage locator device from a laser pointer. This simple circuit is powered by a 6V dc wall wort, adjusting the output to yield 3V dc as a substitute for battery power. A CdS cell "looks" at the garage door opener light and actuates a relay, turning on the laser pointer when the garage door opens. And voila... no risk of front-end damage anymore.

Read Ken Swanstrom's complete instructions on how to build your own Garage Locator Device (PDF).
Garage Locator Device
Amt Part Description Allied Part #
1 Resistor 180 ohms 1/4w 832-0237
1 Resistor 1k ohms 15-turn pot 754-1061
1 Relay 5V dc reed 850-1550
1 NPN transistor 2N4401 568-1946
1 Diode 1N4001 266-0001
1 Photoconductive cell 699-9516
1 Power supply 6V dc 928-9625
1 Terminal strip 924-0100
Additional parts required
Laser pointer(s)
Perf board
4" x 2" electrical box with cover (modified with various holes)
Wire
Fabricated parts
Laser pointer ceiling brackets
CdS brackets
Dowel with brass screw
Brass contact tab for end of laser pointer

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