Tuesday December 9, 2008

A Signal Accomplishment

Harry Homeowner Does 'Lectric

We have a rather decrepit electric stovetop (four spiral burners, circa early-60's) with one small red "signal" lamp to let us know that a burner is on. Unfortunately, said lamp isn't all that noticeable.

It's dim, small, and hidden by a ridge of metal that surrounds the controls, protecting them from spills, etc. So, under the best of circumstances, it's only visible to someone standing immediately in front of the stovetop.

If something gets put on top of the lamp and/or the cook is rushed or distracted, the dim glow may not be noticed until MUCH later. As a result, we've left burners on (albeit at very low settings) for hours after we were done cooking. This is not good; it's dangerous, wastes power, etc.

We knew that we really needed to solve this problem, so we discussed some possible solutions. First, Rich and I would brainstorm. Then Rich would talk the idea through with assorted friends and relatives who (conveniently enough) are electrical engineers. Rinse, repeat...

We first considered the idea of installing a timer that would shut off power to the stovetop after a pre-defined time. In fact, Rich even bought some parts for this approach. However, he eventually decided that it seemed a bit too difficult (and too far from being compliant with the electrical code :-).

We then talked about making the current signal lamp more noticeable (eg, larger, brighter, blinking). This is easier, because it doesn't involve switching 220 volts via timers and relays. However, putting a replacement lamp into the control box seemed a bit dicey (not all that much room) and it still left the possibility of the lamp getting covered by a potholder, etc.

So, Rich decided to add an auxiliary lamp that would light up whenever the main one did. Basically, this involved running 110 volt power out of the control box and hooking up a second indicator light.

The first part was more difficult than it might appear (aren't most projects?). First, the stovetop had to be raised and propped up. Then the power had to be turned off (downstairs, at the breaker), so that Rich could open up the control box and prop it open (I did a lot of the propping :-) for access and consideration.

Then the power had to be restored, so that Rich could make (careful!) measurements. Rinse, repeat as Rich tried out various theories and wiring approaches. All told, it took several hours (and we were without any lamp at all for a while) until Rich was happy with the result.

Now for the interesting part: creating the second indicator light. In a fit of whimsy a few years ago, Rich purchased a Luxeon Star LED emitter. This is quite a bright little beast, when powered at its maximum continuous operating current of 350 mA. By playing with some wall warts and resistors, Rich was able to find a combination that yielded the desired current.

To keep the emitter from frying itself, Rich bolted it to the back of an aluminum heat sink. He then glued a ceramic magnet onto some of the heat sink's aluminum "fingers". This gave him a self-cooling "lamp lump" that would stay any (magnetic) place it was put. (The ceramic magnet was a "find" after discarding an old hard drive. Recycling wins.)

He then purchased a magnifying door peephole (we're nothing if not creative!) and mounted this into the wooden panel below the stovetop. He had guessed (correctly) that the same optics that allow an eyeball to get a wide-angle view would allow the LED to generate a wide-angle (ie, diffused) beam of light.

The interior end of the peephole served as the mounting point for an L-shaped steel bracket; this served as the mounting plate for the lamp lump and wall wart. A slot in the bracket allowed Rich to adjust its vertical position (so that the LED would be at the right height for the opening in the peephole).

With all of that in place, Rich simply adjusted the placement of the lamp lump for maximum coupling to the peephole. Success! We've now been using the auxiliary lamp for a couple of weeks; it is visible from the dining table and lights up the kitchen if the overhead lights are off, etc. It's right purty, too.

Co-written by Vicki and Rich

p.s. Rich built a similar but different detector system for his Dad's gas stove.

A Signal Accomplishment ( in category Show & Tell ) - posted at Tue, 09 Dec, 23:00 Pacific | «e»

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