This project stemmed from a discussion with a friend that said he wanted to be able to listen to music while he was camping but he didn't care for the sound of the portable boxes out there and they didn't have any way to charge them while in the wilderness. I wanted to make a solar phone charger since my phone always seems to die a couple hours into a camping trip. I decided we could combine them and have something that would please both of us.

I went looking for an affordable tiny full range driver with decent bass and found the Dayton Audio ND-65 at Parts Express. I love this driver, with it's aluminum cone it can better withstand getting stuffed into a pack. I already had a TA2024 2x15w amplifier but had to design a charging circuit to round out the required electronics. I went through 2 iterations on the box design, the first one was to test how low the speakers would get in a small enclosure which seems to drop off right around 105hz. But I found I could really shrink the enclosure and tune it to about 75Hz without any major impact on the 105Hz I was getting before. The final enclosure ended up being 12.25"L x 4.25"W x 3.25"H (outside dimensions) of 1/2" birch plywood. The length and width were decided by the size of the solar panel I wanted to use, the height was dictated by the height of the driver.

The exterior was painted with a rubberized undercoating for cars to help withstand some abuse and the elements.

Power is supplied by 8 AA NiMh 2200mAh batteries which are in turn charged by a 12v 1.5A solar panel. The batteries are fully charged at 1.45V per cell or 11.6V total. Open voltage on the solar panel indicated 22V in full sunlight, so I needed to regulate it down to my maximum voltage of 11.6V. This was accomplished by using an LM317 voltage regulator with two resistors and included a diode. The value of the resistors will vary somewhat as you'll need to account for a 0.7V drop across the diode. I believe my actual resistors wound up being 240 and 2100.

The USB charging circuit is another simple circuit using only an LM7805 to output 5V to a pair of UBS ports. This works really well but tends to get warm if you have a really power hungry device, since it's only really good for about 1 amp. I'll be installing a switch on the LM7805 since it's always on and draining the batteries with a tiny current draw.

The audio input is via an 1/8" audio jack from the headphone jack on the phone. This may eventually get replaced with a bluetooth input device since audio fidelity isn't of paramount importance. But as it is I can have my phone plugged in and charging and listen to some tunes at the same time.

My overall listening impressions are that it is way better than one of those small bluetooth portable speakers. It still doesn't get as deep as I'd like but isn't bad for a 2-1/2" driver. Mids are really good and the highs are bit bright but it's smoothing out with use. It does get rather loud, volume is currently completely controlled by your device, though I may add a volume knob because the lowest volume on my phone is still too loud for my cube neighbors at work.

With a full charge I had this playing at near max volume for about 8 hours, the phone was not being charged, and the solar panel wasn't connected.

Step 1: Parts and Tools You'll Need

Parts list:
24" x 24" x 1/2" birch plywood
2 - Dayton Audio ND-65 full range drivers. I used the 8 ohm version.
1 - TA2024 2x15w amplifier.
1 - 1.5w solar battery charger
8 - AA 2200 mAh NiMh batteries
2 - 4 AA battery holders
1 - LM317 IC
1 - LM7805 IC (or get a 3A adjustable voltage regulator)
1 - Diode 1N4001.
2+ - Resistors. These need to be calculated for your voltage.
1 - small prototyping or vero board, like this. Only need half, or less.
1 - barrel jack
1 - barrel plug
1 - USB jack, mine is a double.
1 - 1/8" stereo audio jack
1 - SPST switch
1 - 1/2" x 4.75" PVC tube
Some small screws
misc. wire and spade connectors
wood glue
1 - 12v+ wall wart power supply if you want to charge it indoors.

Tools list:
Measuring tape
Table saw
Drill or drill press
1/2" drill bit for the power switch
5/8" drill bit for the port
7/8" drill bit for the port
2", 2-1/8", or maybe 2-1/4" hole saw or forstner bit for drivers. I prefer the 2-1/8" with some extra filing where the terminals are. 2-1/4" might be too loose.
File
Small chisel or utility knife
Wire cutters / strippers
Soldering iron

Step 2: Construct the Enclosure

Cut list:
4 - 3.25" x 12.25" - Front and rear, top and bottom
2 - 2.25" x 3.25" - sides
1 - 1/2" x 4.75" pvc

The reason for the odd 1/4" is that I wanted the solar panel to be able to rest on top without hanging over, I was also trying to maintain the golden ratio as much as I could.

Cut the peices.

Drill driver, switch, USB and audio holes in the front panel. The driver holes may need a small notch filed where the driver connectors will go. The USB and audio jacks may needto be chiseled out from the back so the fit is tight. I left one ply of wood at the face.

Drill the holes for the ports. Start with the 7/8" forstner bit and drill about halfway through from the inside. Then with the 5/8" bit drill the rest of the way through so that the smaller hole is centered on the larger. This only needs to be done on one side and the hole should be placed near the top and back.

Determine the location for the barrel plug and drill a hole in the back panel.

Temporarily put it together using screws, or just clamps.

Fit your batteries and electronics into place, mount and wire.

Glue everything but the top or back sides to maintain access. My final version is only held together by screws and it seems to be doing well.

Step 3: The Electronics

The TA2024 isn't big but it barely fits in this enclosure with the batteries, port and charging circuit. Plan and test fit carefully.

I failed to get acceptable pics of the charging circuit, but it's a simple affair if you follow the schematic.

I didn't take into account the LM7805 would always draw a small current and drain the batteries if wired as shown. I recommend putting the power switch before the LM7805 to prevent that instead of at the 11.6V Out. It'll require one extra wire and your USB charger will only work when the power to the amp is on, but it's better than constantly draining your batteries. Another option would be to install a separate switch for the USB circuit and run them independantly.