Solar Stella

This is the story of how I made a solar powered Stella Amp!

The solar stella, with the speaker facing the camera and the solar panel propped up to receive sunlight

When I designed the Stella amp a couple of years ago, I realized that I could make the amp run at 3 volts. I knew right then that I wanted to make a solar powered version of the amp. A few months ago, I grabbed one off the shelf and picked up everything I needed from Adafruit to make it happen:

Solar panel
Solar charging circuit
Thermistor. This is a temperature sensor that will protect your battery if you try to charge it in the extreme heat or extreme cold. (You need this if you are going to be forgetful like me and leave your amp in the sun in the hot car all day.)

Of course, everything arrived during The Move, so I wasn't able to put it together for quite a while.

My original plan for this amp was to make a rather rugged poly-coated wood enclosure that could stand up to being left outside in a light rain. On the other hand, I also wanted to finish my amp by the time that the Minne Maker Faire rolled around. I quickly realized that my woodworking skills were not up to the task of being able to make an amplifier enclosure with the time that I had.

I started looking at what cigar boxes I had on hand. I considered a number of them, but ultimately decided on a Romeo and Julieta box that I picked up at a thrift store. It was a hard choice, because this particular box has some very beautiful cover art on the lid (inside and out), and I would have to cover it up with the solar panel. I decided to cover it up with the solar panel anyway, because I could see the original artwork when I opened up the lid.

Mounting the solar panel was just a question of drilling four mounting holes. The Adafruit panel comes with the wrong sized jack, and you have to splice a new jack on, so I cut off the old jack and drilled a hole for the wire, and put that through before mounting the solar panel. Then once the panel was mounted, I soldered in the new jack that is the right size.

I cut out the speaker hole using a Dremel tool (sorry, I forgot to take pictures of that). The holes for the pots were relatively straightforward.

During The Move I managed to lose my 13/16ths bit for the power switch (it's a 20mm power switch), so I just used a 3/4 inch bit and used a round file to enlarge the hole a bit:

A drill bit making a hole for the power switch
The rough drilled out hole for the power switch.
Using a round file to enlarge the hole.

I also extended the status LEDs from the Adafruit charge circuit out to the front where the solar panel is.

The mounting and wiring was fairly straightforward. As far as how, specifically, to set up the solar panel, battery, and charging circuit, I just followed the instructions on Adafruit's awesome tutorial page. I just put a switch between the LOAD terminal and the Stella amp.

I tried to get a speaker grill cloth done but I ran out of time before the show. I kind of bodged it up actually, so I have to come up with a new plan for it. I tried to hold the whole thing together with staples and I ran out of staples and... yeah. It's a mess.

But, the speaker grill aside, I got it done, and it sounds GREAT. It's nice having a portable amplifier that I never have to worry about changing the batteries in.

If you want more information about the Stella Amp, check out the project page. The Stella Amp is 100 percent open hardware, so you can read my step by step design notes or you can download the Stella Amp schematics. If you want to buy a kit, check out the store!

And if you have any questions, post them in the forums!

More pictures (some of these you can see that the yellow light in the front is on, which means it is charging):

A picture of the solar powered Stella Amp, with the solar panel mostly facing the camera.
The amp on the grass, propped open with the speaker facing the cameraThe amp on the grass, propped open with the solar panel facing the camera

Baby photobomb!

My son about to grab the amp in the grass
The Solar Stella, solar panel upSolar Stella, speaker towards the camera

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