I know, I know what you're thinking... not another ipod speaker/usb charger, right? Well, I wanted to document my specific application with an iPhone and with these ThinkGeek speakers. And it just so happens that there is a ThinkGeek contest going on!
This instructable details how to add a dock connector to the Mini DIY Cardboard iPod Boombox available at ThinkGeek.com and made by suck.uk.com. This is a great little set of inexpensive speakers, which combines decent sound and ultimate portability. The speakers run on 4 AA batteries, and have an 1/8" stereo jack for input. I want to add the following features to the boombox:
1. Physical compatibility with the iPhone
2. Audio line out from the dock connector
3. 5V USB charging from the dock connector
4. RF shielding between the iPhone and the speakers
This is my first instructable so be gentle. Let's get started!
Step 1: Parts and Tools
For this instructable, you will need the following:
Mini DIY Cardboard iPod Boombox from ThinkGeek
An iPod Cable with Dock Connector
7805 Voltage Regulator
Various Resistors - see step 4
2AA Battery Holder & Batteries
An iPod or iPhone
Scissors or Blade
Pliers and Wire Cutters
Step 2: Cut the Boombox IPod Holder
This boombox is designed for 5G and older iPods and is therefore not wide enough to accept the iPhone. To remedy this, I simply used a pair of scissors and cut away from the top cardboard edge until my iPhone fit into the cutout. If you're careful, you can make the edges look nice... I was not so careful!
Step 3: Modify the Dock Connector
For this step, I used a Belkin iPod Dock Connector. It was originally designed for use in a car, and features a Line Out connection. I chose this cable for my instructable so that I would not have to solder the line out connections on the dock connector. Open up the plastic backshell of the connector to reveal the connector pins. You can see the audio line out connections on pins 1-2, 3, and 4, with black, yellow, and green wires respectively. The other end of these wires will connect to the boombox amplifier in parallel with the 1/8" Stereo Jack. This way, both the iPod Dock and the Stereo Jack can be used as input for the boombox.
You can use any cable, or even build your own using these connectors. If you are building your own, refer to this webpage for information on the pin arrangement in your ipod dock connector.
My Belkin cable uses 12VDC to charge the iPod through the firewire connection. This type of charging is not supported on the iPhone, so I had to move the power cables from pins 19/20 (12V) and 29/30 (Firewire Ground) to pins 23 (5V) and 15/16 (USB Ground) respectively. Once these wires are resoldered, I will connect the other end to a 5VDC power supply on the boombox. Regardless of the iPod you are using, the power will have to be supplied over the 5V USB connection because 12VDC is not available on the Boombox. It runs on 4AA batteries, or 6V.
The first image shows the connector as it is comes from Belkin. The third image shows what the connector looks like after making the aforementioned modifications as well as implementing the circuit described in step 4.
Step 4: Create a 5V Regulated Voltage Circuit
The boombox runs on a nominal 6 Volts, but the power supply is not regulated. I decided to add two more AA batteries, and run a 5V regulated power supply from the subsequent 9V battery supply. For this, I am using a 7805 5V Voltage Regulator. I soldered in the 2 extra AA batteries at the switch, so the phone only charges when the stereo's turned on.
According to the Pinouts.ru website, the iPhone 3G requires 5.0V, 2.8V and 2.0V on Pins 23, 25 and 27 respectively. The site is also nice enough to tell you how to create these voltages. I have made a schematic, but the credit must go to pinouts.ru.
The iPhone 3G also requires some resistance at Pin 21 to notify the phone that an accessory has been connected. I used at 10k resistor for a dock connector. With this resistor, I still get the error message that this accessory "is not made to work with iPhone", but this is necessary to activate the audio line out on the phone.
In the schematic, the colors aren't important, they are the colors of the wires in my physical circuit.
Once the circuit is created, solder the additional wires to dock connector. I used a 5V bench supply to test my connector. Success!!! As soon as I saw that it was working, I put some hot glue over the dock pins to keep them in place and prevent a short.
Step 5: Disassemble the Boombox
The Boombox is designed to be collapsible, so accessing the electronics on the inside is straightforward. After opening the top and bottom of the box, the electronics board is visable on the side wall, wrapped in a small, crayon-box like package. Carefully pull the board out of this box, noting that the power, input, and speaker wires will still be attached to their respective components inside the boombox.
Once the board is out, identify which cables run to which components. See the image below, with the various cables marked. We will be soldering to the back of the board, where the audio lines come in. There is a left and right channel, with a common ground between them. I did not bother to determine which channel is left and which is right. For this small stereo, I don't think it will affect the sound.
Step 6: Solder in the Dock Cable to the Boombox
With the stereo electronics exposed, we can make make the necessary connections to the board. Following the schematic in Step4:
Solder the new battery pack to the power switch.
Solder a ground wire to the battery pack ground.
Solder the audio channels and ground from the dock cable to the inputs.
Step 7: Create RF Shielding
Anyone who has an iPhone and has tried to play music through external speakers knows all too well the horrible sounds produced by RF interference or Electromagnetic Interference. As far as I understand it, radio waves emitted from the phone are picked up on the amplifier circuitry and come out of the speakers as noise. I am going to attempt to reduce this interference by adding a metel barrier between the phone and the speakers. The metal is placed between the line-of-sight of the iPhone and the boombox electronics.
To start, take some empty Aluminum soda cans and remove the top and bottom with a pair of scissors. Then flatten the remaining ring of Al. I used the outside edge of my scissors to create a sharp fold. Fold the flat sheet into a hat section, using your phone as a template (see image). I used hot glue to hold it in place inside the box.
So how does it work???
Meh, I don't think it made a difference. Next, I will try using steel sheet instead of Aluminum, but after playing around with this, I think that the noise may come from conducted EMI on the audio lines.
Step 8: Reassemble
Now that there's a rat's nest of wires and components, stuff it back into the cardboard housing. I used hot glue to bond the new battery pack and voltage regulator to the back face of the boombox.
With the iPhone installed, I cut a slit in the cardboard where the dock connector protrudes. When I had the connector lined up, I used hot glue on the bottom to hold it place. As you can see, the phone slides in asymmetrically, so the dock connector is also offset. That adds character, right?
Now add the mods are in place, just fold the box back together and you're done!
Step 9: Enjoy!
Everything's hooked up and running now. One issue I ran into is that the line output on the iPhone is at a fixed volume. The cardboard boombox has only 3 volume settings, which makes for some loud music enjoyment.