Ken put an end to expensive car damage
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.
This Gadget Master was originally sourced from our sister publication, Design News.
There are many methods used to locate automobiles in a home garage space, the most common of which is suspending a tennis or golf ball on a string from the ceiling. The ball is usually located so that it just touches the windshield when the car is in place. This ensures the car is inside the garage door, but not too far so as to reduce clearance in front.
The problem with this method is that it is car specific, since the ball is suspended in a fixed position, and since the ball is usually hung in the center of the parking space, it is very difficult to adjust when the car is in place, or when another car is parked in the same space.
To improve on a locating method, I thought of using commonly available laser pointers which could be mounted to the garage ceiling in front of a car. These lasers are normally powered by two internal “AA” or “AAA” cells, which together yield 3vdc. I built a simple circuit powered by a 6vdc wall wort, the output adjusted to yield 3vdc, as a substitute for the battery power. I then needed to turn on the laser pointer when the garage door was opened. So as to not to tie into the garage door opener circuits, I used a CdS cell to “look” at the garage door opener light and actuate a relay, turning on the laser pointer when the garage door was opened.
Brackets were fabricated using brass tubing and flat stock, available at most hobby shops. One bracket attaches the laser pointer to the ceiling at a location 3 feet in front of the car, allowing easy adjustment when the car is in place. Tubing, of a diameter that is a slip fit over the pointer, was soldered to flat stock, which in turn, was attached to an “L” bracket, providing attachment to the ceiling. This tubing also served to depress to the “on” button of the pointer.
The other bracket, also comprised of brass tubing and flat stock, locates the CdS cell approximately ¼” from the door opener light housing. The CdS cell was placed inside the tubing to eliminate interference from ambient light.
The only modification to the pointer was to drill a small hole in the pointer end cap so an insulated wire can pass through. A wooden dowel of a diameter and length that duplicates the batteries’ diameter and total length was drilled through and fitted with a brass screw which also was drilled through, to which the wire was soldered, this assembly then became the center contact.
A small brass tab was fabricated that had a small, drilled hole to which a wire could be soldered, and a larger hole that just cleared the threads of the pointer cap. When the cap was tightened down, this tab formed the other contact of the pointer circuit.
The relay control board was housed in a standard 4″ x 2″ electrical box with appropriate grommeted holes for the various wires.
Note that with most laser pointers, the batteries are inserted with the positive end towards the end cap, and thus, the brass tab attached to the end cap is positive. Also, most laser pointers incorporate a circuit to prevent damage to the laser diode in the case of battery reversal, so when the 3vdc is applied, if the laser does not light, simply reverse the wires.
One adjustment is necessary – check that the voltage across the laser supply terminals is a maximum of 3vdc and adjust R2 accordingly.
|1||R1||180 ? 1/4w|
|1||R2||1k ? 15-turn pot|
|1||Q1||NPN transistor 2N4401|
|1||6vdc wall wort|
4″ x 2″ electrical box with cover (modified with various holes)
Laser pointer ceiling brackets
Dowel with brass screw
Brass contact tab for end of laser pointer