Over the holiday I was watching my usual raft of videos on Youtube, and got interested in the circuitry that is inside the common garden light. I have a number of super cheap $1, and if you watch any teardown videos of them, you’ll find that there is almost nothing inside them: typically a solar cell, a battery, an LED, and an inductor and usually a small 4 pin chip. I was interested in running some experiments, so I disassembled one of mine which looks like this model. I hooked up the solar cell to my multimeter, and measured about 2.5v at 12ma or so, for about 30mw of output power. The chip inside was a YX8018, and it also had a AAA NiCad battery which tells me it’s capacity is 160maH. Tiny.

These lights seldom incapable of maintaining a light (even as feeble as it is) the entire night, but I was curious about the circuits, so I went ahead and decided to try to experiment with them. My ultimate goal is to characterize the cheap solar cells, and also monitor the charge cycle of the battery. In the next few days, I’ll setup an Arduino as a data logger, and measure how the current flows in the circuit over a couple of days.

I could have used the scavenged components, but I thought it might be fun to start from scratch, and be able to make several versions of the circuit to compare and contrast. So, I ordered a pack of 20 QX5252Fs (a similar chip to the YX8018, but cheaper) for a little under $2 shipped from China. I had a couple of 100uH inductors lying around, as well as some fairly bright white LEDS. So, I breadboarded the circuit up. Instead of using the tiny AAA battery, I thought it might be good to use a reasonably high quality ENELOOP NiMH battery. Using the simple curcuit from the QX5252F datasheet and some scraps of wire, I put it up on my workbench:

It works. So, over the next few evenings I’ll begin to experiment with it some more. I wanted to experiment with changing the inductor (which modifies the LED current) and perhaps driving more than one LED to make a brighter light. I’m also interested in potentially using this setup to make a very small solar powered microcontroller project, using some additional circuitry as described here. More experimentation is clearly possible.