Introduction: Solar Powered Tunes and Phone Charger

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.

Comments

author
jlightcap9 (author)2014-12-19

Thank you for your feedback. So I am having trouble getting the 11.6 volts you described because I couldn't find a 2.1k resistor in time for Christmas. I do have a 12 volt voltage regulator though. Is it ok for me to use the 12 volt voltage regulator and just the diode which as you said steps down the voltage to around 11.5? I know the regulator needs at least 2 volts more than 12 to produce twelve, and should step down if voltage is less, but should be able to handle the possible 20 in from the panel. I am very new at this so any input is awesome. Do the resistors add some level of protection to the batteries that the voltage regulator doesn't by itself? Thanks this project is so cool.

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author
jlightcap9 (author)2014-12-04

Hi! I am attempting to construct this as well. I love it! I have been bread boarding the circuit design and think I have it down as this is my first venture into the world of circuitry. My question is, do you plug the solar panel into the charging circuit when you desire to charge batteries via solar and unplug to plug directly into the wall for indoor listening?
Here is a picture of what I have so far. I am welding a frame out of angle iron and attaching plywood faces afterward.
Love this, thanks!

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author
Gyvven (author)jlightcap92014-12-04

That looks really slick.

If your solar panel is integrated into the unit you can hardwire it to the pcb, and because it has its own blocking diode you can connect after the diode on the pcb. Mine was set up so I could disconnect the solar panel and plug into the wall. The thing is that you make sure the solar panel isn't back feeding into the jack, unless you want it to. I don't recommend charging with the wall wart for long periods unless your voltage is really conservative. I cooked my batteries by leaving it charging for a day. I'll be posting an update with version 3 or 4.

author
ourgangmn made it! (author)2014-03-15

I love your idea. I am trying to make one, but using a Lepai amplifier from Parts Express that includes a volume control and 3 1/2" speakers. I also am concealing the edges of the solar panel in grooves at the top of the wood sides and ends, making the solar panel the top of the box. I put in a 2k resistor along with the 240. My voltage is 11.1V. Is my resistor too large?

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author
Gyvven (author)ourgangmn2014-03-16

Hey ourgangmn,

Nice work. I'm considering doing another project using the 3.5", myself. I like your idea of using the solar panel for the top.

Your voltage ideally should be about 11.1 up to 11.6 after the diode. Remember the diode will drop about 0.7V. Your11.1V should be adequate, you'll get the cells up to about 1.38V each and not overcharge them.

Below is the mk2, or maybe it's mk3, Where I've incorporated a cheap BT/FM tuner/SD reader and USB. I still have the Aux input and an extra USB charger on it and it's about 40% smaller than the one in the instructable. I haven't noticed any ill effects from the smaller size (10.5"x3.25"x3" outside, 1/4" mdf), but the Fb of the box is about 80Hz, well below where I expect it to roll off. It's still not pocket sized, but it's much easier to haul around. I'm also using a cheap Boost/Buck regulator off ebay. It'll take any voltage from 3-35 and output the 11.6 I want. Though it gets a bit warm when plugged into the wall, because it's only rated for about 0.6A. I'm sure my small solar panel won't cause that problem. I also really like my new laser cut box, I can draw my template and have it cut exactly the way I want it and not have to rely on my dubious woodworking skills. I'll eventually get around to making an update to this instructable about this.

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author
ourgangmn (author)Gyvven2014-03-18

I'm not quite sure what I'm doing wrong, but my batteries do not appear to be charging. My circuit is basically what you posted, but as soon as I unplug form the wall or bring it inside...no power.

author
Gyvven (author)ourgangmn2014-03-18

And you verified you're getting 11.1V between +V and Gnd after the charging circuit? Check this without the batteries connected. Also, double check your diode isn't turned around.

You should be able to run your box while charging. If you can do that but you're not getting power when just on batteries I would suspect a bad connection in your battery holder (which I've come across in mine lately). I had to use my multimeter to track it down and I found one of the tabs was slightly off the + side of the battery.

author
ourgangmn (author)Gyvven2014-03-18

OK, I discovered my battery connections were a bit suspect. Both battery holders have one battery that can keep the spring compressed on the negative end without pushing the positive end of the battery against its terminal. Also had to repair my negative lead since the glue that was holding my battery holders in place let go and the negative wire pulled away from the board when the battery pack moved. Fixed both problems and...it works!

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