[Geek Alert…]

I’ve been on a roll fixing up and beautifying the front and back yards here at Casa del Garrett.   Among other items, I bought four solar powered Tiki torches for the backyard.   They’re pretty simple devices consisting of a solar power cell and two led lights that flicker alternately inside a plastic cup.   The effect mimics a lighted torch well enough and I think they add a nice touch to the backyard.   The other day one of them failed.

It was always the last one to come on at night and I wondered if the rechargeable batteries in it just needed replacing.   So the first thing I did was put some alkalines in it as a test.   Nada.   I checked its internal wiring.   The things were Very inexpensive to buy and inside it showed why.   Just a postage stamp sized circuit board, a double-a battery compartment, a nice looking solar power cell and a smaller cell that looked as if it were a CDS light sensor for switching the torch on and off.   The parts were simply hot glued into place and the wires connecting everything were a gauge somewhere between hair and paper width.   I got out a magnifying glass and looked the connections over with some difficulty as it was hard to see how good they were under the hot glue globs.   But nothing seemed obviously broken.

As I said, they were cheap.   So I figured I’d go buy two more (they come in pairs) and then I’d have one spare in case one of the others failed.   Having bought the last two boxes of these on the shelves at the Lowes in Cockeysville, I figured I’d need to try one of the other stores.   So this evening after work I drove to the one in White Marsh so I could swing by Costco for some gasoline.   But that Lowes was out of stock on those particular Tiki torches.   So I began to wonder if each store only got a couple boxes of those at the start of the season and was I chasing an item that was sold out all over the area by now.

I came back home and considered ordering new ones online. But the ornery techno geek in me nagged at me to look inside the broken torch one more time.   It’s a simple device dammit…I ought to be able to fix it… So I brought it in and took it to the art room drafting table and opened it up.   I got out the multi-meter (you have one of those…right?   Every home should have a multi-meter…) and fairly quickly determined several things.

First, the rechargeable batteries were in perfectly good shape, as I’d expected since replacing them with some stock alkalines didn’t make any difference.   Second, the solar power cell in those things, cheap as they are, are Very Nice and were putting out more then enough voltage to keep the batteries charged.   After the batteries, my suspicions fell on the other small cell that looked like a light sensor.   Here was where I reached way back into my past for knowledge of how camera light meters work.   It looked to my eye like your basic CDS cell…Cadmium-Sulfide…a photo-resistor.   Unlike the older selenium cell meters, which generate a precise voltage based on the amount of light falling on them, CDS cells change in resistance.   Their advantage was they worked better and more precisely in lower light conditions.   What was extra nice about them back in the day was if you forgot and left the camera’s light meter on, putting the lens cap on or just putting the camera away in darkness somewhere would protect the battery because a CDS cell goes to maximum resistance when there is no light falling on it, so it’s basically turned the circuit off.

…which is pretty much what makes them useful as light sensors for turning off and on stuff when night falls.   They can act like a simple on-off switch.   The leads coming off the CDS cell in my Tiki torch were buried under a glob of hot glue so I traced the wires back to the circuit board and took an ohm reading there with a piece of black electricians tape across the cell blocking the light out.   It should have read max ohms but it read like a short.   So the cell was defective.

I clipped the wires leading to it and the torch lit up.   I stripped the ends and touched them together and the torch turned off again.   So now I can either put a micro-switch in place of the CDS cell or see if I can find another CDS cell to replace the failed one with.   This thing is so cheaply built you just know the concept it represents is throw it in the landfill when it breaks or you get tired of it whichever comes first.   Had I found a replacement I’d have probably just scavenged the solar cell and the LEDs and tossed the rest out.   The solar cell is a nice one.   But fixing it leaves me with a degree of geeky self-satisfaction.   In a world of cheap mass-market throw it away goods I am not completely helpless.

[Edited a tad…]

[Update…]   I see from their online catalog I can buy little CDS cells in packs of five for a little less then four dollars at Radio Shack.   So tonight I’ll check the one in my neighborhood.