Case #90: Ken Put an End to Expensive Front-End Damage
Design News Staff -- Design News, September 24, 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.
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Read Ken Swanstrom's complete instructions on how to build your own Garage Locator Device (PDF). |
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| 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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To answer some of the comments:
The laser pointer is mounted on brackets to allow side-to-side and up-and-down adjustment, and is mounted on the garage ceiling approximately 3 feet in front of the car so that adjustment can be made (on a stepladder)with the car in place. The beam is aimed so that when the car is in its proper place, it shines through the windshield and hits the middle of the dash. Select a metal-cased pointer - cheaper plastic-cased units do not dissipate heat and since my door opener light is on for approximately four minutes, so is the pointer. Laser pointers have a built-in diode to prevent damage in the event batteries are inserted backwards. Thus, when applying the dc power, depending on the polarity of the connection, either the pointer will work or it won''t. If it doesn''t, simply reverse the wires. Regarding the pot, before applying any power, use an ohmmeter and adjust the pot to its maximum value. Then, after connecting one or more pointers, connect the power and adjust the pot to yield 3v. This system has been in use in my garage for approximately six months and has worked perfectly every time. And yes, this is not recommended for households where there are children. Finally, wall wort and wall wart seem to be used interchangeably. Both can be found on the Internet to denote a plug-in low-voltage power supply.
- 2006-29-9 15:37:11 EDT -
interestin topic...
- 2006-28-9 03:54:31 EDT -
great article.
- 2006-28-9 03:46:27 EDT -
Where does the laser point (car hood, bumper)? Where is it mounted (ceiling pointing down, wall pointing side ways, floor pointing up)?
How does it tell you the car is in place?
- 2006-27-9 10:36:25 EDT -
Greetings,
I live in an area where power failure is a daily occurance. Plus, I do not have a garage door opener. I use two tennis balls to remove parallex and correct for distance as a single ball touches windshield.. How does you gadget over come my problems?
Sincerely,
Tom Grosch
e-mail: tgrosch@cox.net
- 2006-27-9 06:40:35 EDT
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