Intro: IPod Powered Amplified Speaker
When looking at a pinout sheet for Apple's propriatary connector, I noticed something that got me excited- a 3.3 volt output! Originally intended to power accesories such as the early plug-in cameras, I realized this could be hijacked for a different purpose- to power an amplifier. This idea led to the birth of the microJammer.
The microJammer is a small, amplified iPod speaker. since it uses the iPod's battery for power, the speaker's size is very, very small; less than an inch in any direction. It uses a common 2 transistor amplifier circuit, and uses the headphone jack as the signal input. It is by no means a micro sized boom box, but the volume is comparable to an iPod touch's internal speaker, with the sound being a little more bassy and clearer. Seeing as it relies on the ipod's internal battery, the iPod's battery life is cut down drasticly, so this is not intended to be used all day. But for sharing music with others on the go, this cant be beat!
Step 1: Parts and Pieces
The ciruit uses only 5 parts (not including the speaker)- all very common and easy to find. the parts are as follows:
NPN Transistor- 2N3904 or BC548
PNP Transistor- 2N3906 or BC327
10 uF capacitor
4.7k ohm resistor
1M ohm resistor
As for the driver, the smaller the better- to a point. You dont want to use a driver from earbuds, or a super cheap driver. Drivers from over-ear headphones are great, as well as speakers form portable DVD players. I got mine from one of those. They are Panasonic brand and actually have very good sound. A good way to tell what kind of driver would be best is by what it was from- if you find a driver used by something that plays audio, it would probably be a safe bet for this application.
Other parts that are needed include:
1/8 inch headphone plug (from old headphones)
A word about the ipod connector- I recommend vandalising a USB cable for the connector, but DO NOT use a new cable. The new one has contacts in the connector only for the USB functions- USB power +/-, and signal +/-. The older connectors have all of the contacts in the connector in place, including the one we need to power the speaker.
And as for the enclosure- Anything small will work. I was originally going to use an altoids tin, but it was too big. (what does that say about the size of this thing?) So next I tried a Tic-Tac container, which as difficult to cut a hole for the speaker, so it was scrapped. I then came across the top part from an old flashlight, which was the exzct diameter of the driver I was using, so i chose that. If you end up using something mad of metal like I did (in my case anodized aluminum) make sure that the amp does not accidentally short circuit against the side of the enclosure.
Step 2: Build It!
The schematic is very simple and is shown in the pictures. If you end up using a small enclosure, don't bother with breadboards, just solder everything together. There are some important notes to consider while building the speaker:
When building in an enclosure, plan ahead. You would want to solder the cable for the plug through the whole in the enclosure before it is soldered to the rest of the circuit. This thinking also applies the the speaker connections and the iPod connector.
When harvesting the plug from the headphones, you will have to solder the wires to the circuit. This can be difficult sometimes. First start by stripping away the insulation from the outside of the cable. This will expose three wires, which are bundles of enamel-coated copper wires. To remove the enamel, start by burning it off near the tip with an open flame from a torch or match. Dont let the enamel burn all the way down the lenth of the exposed wire, because this can cause a short circuit. Once some enamel is burned off, lightly use fine-grit sandpaper to clean the wires. Twist the two positive wire together, which are the two that are not completely copper colored, and tin them This combines the right and left channels into one. Do the same to the single negative wire, which is all copper-colored. The jack is now ready to be soldered to the rest of the circuit.
And now for the ipod connector. Clip the wire off of the connector, and remove the white casing around it. cut off the connections used by the USB. We now need to find pins 18 and 16. 18 is the 3.3 volt +, and 16 is one of the many grounds. It is the ground usually used by the USB connection. The pins are as follows, with the connector plugged into the ipod and the ipod facing upwards:
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Solder wires to the pins can be next to impossible, since the pins are usually cut short, leaving just a small pad available for soldering. I find the best method is melt solder onto the tip of the iron, and then place it on the pad to tin it. Then, tin the wire that wil be soldered to the pad. Place the wire on the pad, and with the tip of the iron clean of any excess solder, heat the connection. The connection will be weak as this method does not use much solder, so it is best to then cover the area in hot glue to protect it.
It is now time to put everything in the enclosure. I mounted everything in the flashlight bezel, and then put in a plastic "spacer" with a notch cut in it between the ipod connector and rest of the circuit. Hot glue was then added above the spacer, potting the connector inplace so it could not come lose and break connection with the rest of the circuit.
Step 3: Finishing Touches
I found that after building the entire speaker, there wasnt quite enough room between the iPod connector and the headphone jack. To solve this, the headphone jack had the rubber strain releif cut off, and the plastic pottin heated up to allow it to be bent. This prevents the cable from being bent a sharp 90 degrees and the wires rubbing together internally, which could lead to a short. It was then shrink-wrapped to protect it.
Step 4: Use It!
I find it easiest to plug the headphone jack in first, followed by the ipod connector, and to unplug the speaker to just do the reverse. The circuit draws current whether or not music is playing, so it is not a good idea to leave the speaker plugged in when not in use. This speaker is also not compatible with all ipods. I've tested in ona 6 gen, 5th gen, and 3rd gen nano and it worked with all of them, but it won't work with an ipod touch. As for other iPod models, I have no way of testing it, but I dont see why it wouldnt work with an iPod Classic. On the 6th gen ipod nano, with its smaller battery, the speaker tends to drain it relatively quickly (within an hour of continous playing) but after letting the ipod sit while turned off the battery seems to recover, and will return to about half full. On the 5th gen nano, playback is closer to 2 hours.
Also, dont rest the ipod on the speaker vertically, since this reduced perfromance. The microJammer works best with the ipod laying on its side, and the driver facing the listener. Since the ipod connector is what essentially holds the speaker to the ipod, be careful not to put strain on it and break the speaker/iPod.
The reason for using the audio from the headphone jack instead of the line out from the iPod connector is simple- volume. The volume is controlled from the iPod as it normally would be for headphones. But the volume cannot be turned up all the way. For best sound, I would not recommend going over 1/2 to 2/3 volume. 2/3 is almost too much as it is. Turning up the volume too high causes the circuit to start clipping, which leads to distortion to the point at which the music becomes almost all static.
Below is a link to a video demonstrating the microJammer:
Congratulations on the completion of your new microJammer!