Steve’s Hacking Blog

This idea has been in my head since I first got my iPhone. When I get into my car I want a super cool place to stick the phone so it not only charges, but connects to my car stereo and plays music and stuff. Being the geek that I am, I didnt even bother checking if one existed. I just started plotting and designing my own. Actually, it’s not that difficult at all.

UPDATE The first prototype is finished and installed! It works perfectly! Pictures soon I promise.

THEORY - what I need
Basically the device needs to do at least two things. One, it has to convert and regulate the cars battery voltage to a standard 5-volt supply. Since the cars voltage fluctuates wildly from 11.5 to 14.5 during various usage scenarios, a 7805 regulator, a heatsink, and a couple of capacitors is sufficient.

The phone also needs to send audio through its line-out connector. This requires a 68K resistor to take the accessory pin on the iphone dock connector to ground, making it think a speaker set is attached. Not having a 68k resistor, I set a 100k variable to 68k and glued it in place. Of course, for all of this to work, the car stereo must have an auxiliary input connector. Mine has one in the front, but not the back. I will mod this later.

OBSTACLES - what I need to fix
The iPhone is very peculiar about its charger though. Simply pushing 5 volts to the USB power pin doesnt start the charge function, like in previous ipods. The data pins have to have a specific voltage pushed to them as well. This requires a resistor network. One pin needs 2.5v and the other needs 2.0v. This will notify the iPhone that it may draw power from the USB. I read somewhere that a guy simply routed the D+ to the D-, making the iPhone talk to itself and force a charge. I tried it, and it works without any issues!

After looking at the specs and pinouts for the iphone, I not only came up with a working prototype, but added other neat features as well. For example a switch inside the holster that cuts off power when the phone is removed, a usb-a female port for other usb-based gadgets (a friends phone, for example), and a small LED that is powered directly by the phone to let you know its seated properly, whether the phone is charging or not.

MOUNTING - attaching it to the car
For mounting, I have a hollow bolt that I can pass wires through, and will also hold the dock to the dashboard and allow me to rotate. It will be a more or less permanent install. It would probably be easier to place said bolt in one of the blank button panels on the dash. All this device needs is a 12v supply and a ground, and it’s only output is a stereo audio output. Please note that a car’s voltage is not exactly 12 volts. It fluctuates wildly between 12 and 14.5 volts during various usage scenarios. Design your car devices accordingly. For example the 7805 regulator can transform anything between 6 and 18 volts to a solid 5, which the phone requires.

UPDATE I finished the first prototype and installed it in the car. Its a tad not-stylish (made of glue and electrical tape), and it doesn’t sit on top of the dash, but rather in front of it. I found a small blank button panel between the two center vents in the middle of the dash, and so mounted my device to that so it could still be easily removed. The bolt could only fit 3 wires, and I needed a fourth for ground. I decided to make the bolt itself the ground and solder wires to it directly. I havent received an RCA-unilink adapter for the sony stereo yet so a single wire is passed in front to connect to the front AUX (my model doesnt have a rear AUX input). When the next prototype is done, it will be more clean and more eye-friendly.

I set the phone to disable auto-lock, so the screen stays on and allows me access to the next, pause, and various other juicy touch-screen functions. Normally keeping the screen on would drain the phones battery, but its being charged continuously from the dock. Its very neat to start a car, place a phone in its dock and immediately hear your phone’s music through the stereo. The only thing I have to keep in mind is turning off the screen manually when I step into a store, otherwise it becomes a magnet for smash-window-grab-phone punks. I have not yet tested receiving a phone call, because people dont call me that often. I assume speakerphone mode will be necessary.

Pictures soon.

Wiring diagram here: http://stevediraddo. … ent/images/idash.jpg

Bill of Materials
plastic iphone protector - 99 cents at local dollar store
some wire - had lying around from old car alarms
7805 regulator - $5.99 at the source (canada’s radio shack)
heatsink - came off an old video card
2 capacitors - came out of an old VCR
iphone dock connector - came from a $9.99 3rd party ipod cable
cutoff switch - from a really old CD-ROM

Assembly
First I glued the plastic iphone protector shut, and cut the top 1.5” off. This makes a nice dock you can slide the phone into. Then I took apart an old ipod cable to get the dock connector. I soldered the extra wires I needed to the proper pins (see diagram above). I put the phone in the dock, and plugged the new homemade cable into the phone through the hole in the bottom. I glued the connector to the dock in place, so it would be perfectly lined up. When the glue was set, I removed the phone and reinforced the glue. I drilled a hole in the back of the plastic dock, and installed the cutoff switch. This switch closes when the phone is placed in the dock, and feeds power to the regulator for charging. All thats left is to place the LED, run the wires, and make it more or less eye-friendly.

Any questions feel free to ask. I will do my best to add some pictures of how I did this.