Light me up, Scotty

The other day a coworker sent me a fascinating article about solar panels and the electric grid. The next day, I woke up wondering how much solar it would take to power some simple electronics, like outdoor cameras for surveillance. And then I realized I had some solar panels literally in my backyard. These guys:

They’re your garden variety (ha) solar walkway lights. They’re about four years old, and my complex’s landscaper has done an excellent job destroying them over the years. What they do is they take in light during the day, and then they light up at night. This means they must have some sort of battery, light sensor, and LED, along with the solar panel. Not bad for ~$2. I decided to take one apart and find out what it was made of.

The screws were a bit weathered so getting them out took a bit of finagling, but with just the first one I found the battery. Unsurprisingly it’s rechargeable. It provides the load to the solar panel, which is what makes the circuit work at all.

The glass ball was just sealed onto the plastic and came off with a bit of wiggling, likely made easier because of the age of the thing. Removing three screws on the outside of the base and one screw on the inside released the shaft from the rounded part of the base, making it easier to remove the tiny circuit board from the fixture. All told, I ended up with this:

A solar panel, a resistor, an LED, and a battery, and a circuit to connect them all. Immediately, I noticed something was missing – where was that light sensor I assumed existed? Then I realized that the solar panel literally collects light, so a circuit would be able to tell if it was light outside or not based on whether there was power flowing out of the solar panel.

I reassembled the thing to see what sort of voltage was coming out of the solar panel, and to see what voltage was powering the LED. In lieu of a nice enclosure, my cute duct-tape job held the contacts to the battery so that the circuit would be complete.

First thing I noticed was that the LED was getting about +1V regardless of whether it was active or not. That seemed strange. But the same coworker who sent me the article on solar panels happens to be amenable to stupid questions, and he explained that the resistor is current-limiting the LED. Things started to make a little more sense. He also sent me this video to watch, and things started to make a lot more sense.

That black blob on the back of the board probably has some extra components underneath it. I’m not sure what I’m going to do with the solar panel yet, but I might try scraping that blob off somehow and recreating the circuit on a breadboard so I can play with it a little bit better and see what else I can power using the solar panel. I may also take apart the other solar light I have and see what kind of trouble I can get into trying to use more than one panel to power a circuit.

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