[Michael Mogenson] built Firefly Jar – a simple circuit to light up flickering LEDs inside a standard Mason Jar, to give away to friends and family for the holidays. Given it’s simplicity and through-hole design, it’s an ideal project for a “learn to solder” class or for those wanting to get started with building some really simple electronics. There’s just a handful of parts and putting it together shouldn’t take long. Given that he’s made available all of the source design files, it should be easy for others to spin off the project.

A 55mm solar cell fits on top of the 63.5mm diameter PCB, which in turn fits perfectly in a standard Mason Jar with a collar lid. When in the light, the solar cell charges two 1.2V NiMH batteries. This also switches off the P-channel MOSFET, turning the LED’s off. The LED’s are turned on only when the solar cell voltage is low and the Ni-Mh batteries are charged. A 2.1V LDO directly drives the two LEDs with built-in flickering circuits, eliminating the need for any further parts. Check out the video of the Firefly Jar below.

Hi Where will you find the 63.5mm diameter PCB ! .

Find a 63.5×63.5mm board and round the edges off.

Like that. Might need to try this and see if I can add a flicker/non-flicker switch.

Is it right that he charges two NiMhs with 5V directly? If the Akkus are loaded and the sun keeps on shining, thats should be problematic.

The program should be different for fireflies than for candle flicker, which is what this seems to demonstrate. Same hardware though.

True. Fireflies are also more of a yellow/green color, and not yellow/orange (like a candle). I like the simplicity of the project, though! I also like the fact that it’s organized well – he even provided the Gerber files! :)

Also, he’s using “candle flicker LEDs” that already have a small chip built-in for the flickering effect.

I thought it was awesome, until I saw Tenergy batteries. They are some of the lowest quality cells I have ever seen.

In the spirit of hacking… you can get solar garden lights for about a dollar each at the hardware store. I’ve made a few lights like this with zero soldering (granted, no flickering)

You could just buy one for a $ at the $ store then modify it with a flickering LED.

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