This instructable shows how to power a mini amplifier with a solar cell and save batteries. It's perfect to use when you're outside and want to hear music. It will play all day long, except the night! ;-)
The mini speaker was given away as some kind of promotion from a famous potato chips brand. You had to send in three cap lids and got an amp free. But I guess there are a lot of similar amps on the market, so if you didn't get one of those, get another one...
You need a mini-speaker
a solar cell 4,5V 80mA (the bigger the better)
an empty chips box and a bit wire and a soldering iron.
Step 1: Unscrew the Battery Housing
There are two ways to connect the solar power to the amp. The first is straight to the springs in the battery housing. This is very easy, you don't have to open the housing, but the disadvantages are: The cable is inside the box and you can't use batteries once you soldered cables to the springs. If you don't solder the cables but use clamps, the whole thing looks rather sluggish.
This is why I chose to open the housing. And of course also to see what is inside. ;-)
So unscrew the three little screws on the side of the housing. Then carefully lift up the upper part. Be careful because there are short cables connecting the two parts! As seen in picture 3!
The last picture shows the heart of the amp: The LM4871 amplifier-IC, but that may be a theme for another instructable.
For now on we continue to power it by a solar cell.
Step 2: Make a Hole Into the Cap
Now you have to drill a small hole into the cap. I chose to go near the audio cable and drilled a small hole in it. Then I also made a notch into the plastic rim around the speaker for the cable. Like the audio cable I made a small knot to relieve pulling forces from the soldering points.
Step 3: Connect the Power Cable
No you have to trim the cables to the suitable length and solder them to the connectors on the back of the battery pack. Make sure not to disconnect the other small cables, because these go to the amp.
If you know that you would like to operate is with solar and batteries you should think about installing a diode to prevent the current from the batteries flowing through the solar panel. But I didn't want to do this anyway so I left the diode. You can even install the diode directly at the solar panel, you don't have to install it in the housing itself. The diode will take 0.7V from your solar cell, but the speaker also works down to 3V, so this is no problem.
Using a bigger solar cell with more power will let your speaker operate even in a shady environment. The 4,5V 80mA solar cell cost me 7€ straight from china and works well only in direct sunlight. With a bigger solar cell you could also think about powering your mp3-player too. But that is now really far beyond this instructable.
Step 4: Close and Test
After I closed the housing again I started a first test and it worked perfectly! With the small solar panel attached it even fits into the old package, but that is not what it is made for. It is made for entertainment and fun in the sun!
The tube provides a certain closed air space for the speaker and the sound is really good for such a small device. Before it distorts the volume is loud enough to entertain a small group.
To the tube itself I added a small iron wire with a loop to be able to hang the whole speaker into a tree, for instance when you harvest fruits.
The wire can also be used to hold the solar panel to which I added a small magnet.
Now you can lay yourself into the sun and enjoy music all day long.