So you've got this great little MP3 player or Ipod, but your old-school car only has a CD changer? Sure you can get an FM modulator, but they don't work so great and are notorious for poor sound quality. I decided to leverage the CD player in my car to add a CD-quality auxiliary input for my MP3 player.
What you need:
-- Stock car stereo with a CD changer input
-- Basic Soldering Skills
-- Soldering Iron & Solder
-- Hand held Volt/Multimeter (to find right wires)
-- Small gauge speaker wire (anything around 18-14 gauge will work)
-- 2 panel mount 1/8" stereo phone jacks ($2.99 for 2 at Radio shack)
-- 1/8" stereo plug cable ($5.99 at Radio Shack)
-- Old pair of headphones (really just need the wire & 1/8" plug)
Essentially what you are doing is sending a pirated signal from the MP3 player onto the line that would normally be sending audio from the CD changer. In order to prevent a mixing of the audio from the changer & your new pirate Aux input, you have to play a special CD which contains tracks with perfect silence. It may sound complex, but is quite simple with some basic electronics/soldering skills.
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Step 1: Remove Your Stock Radio From the Car
This is probably the biggest challenge in the whole project. If you do any work on cars, then your shop manual will help, but also there's tons of user forums dedicated to specific car models. Google around a bit and you should be able to find tips & help.
You may also try calling local car audio shops and ask them for tips on how to remove the radio from your specific make/model. Most are moderately friendly and will give you tips, just don't expect them to come do it for free or anything.
Step 2: Locate the CD Changer Plug & Pins
Locate the CD changer plug and gain access to the pins for audio transmission from CD changer to head unit. It should be something like the socket below in the lower right hand corner. They usually have about 8 or so pins arranged in a circle.
Now here's where you have to do a bit of googling. Figure out what the pin layout is for your radio's CD changer. Try searching with something like "Honda Accord 1996 CD changer pinout" I was able to find this layout for an Acura which was close to my Honda for the basis of mine. Remember, there's only a couple car makers, so there's a lot of similar equipment out there across brands. Honda Civic may be close to the Accord, and also close to an Acura. The same should apply for domestic cars made by the same manufacturer.
The 3 pins you need are:
Step 3: Solder in Aux Input Jack
Once you have identified the audio pins, find a place to mount the internal jack. Using short pieces of small gauge wire, solder connections from the pins on the stereo to the pins on your panel mount 1/8" audio jack. Be sure to keep the signals correctly matched to the right pins so you don't end up crossing channels or ground.
Step 4: Mount the External Jack in Dash
Now that you have the internal jack mounted & wired, find a nice location in the dash where you will mount the external jack to plug in your MP3 player. Carefully drill a hole in the dash just larger than the jack to mount the external jack.
Use the old headphone cable and cut to the appropriate length to connect the internal and external jacks. Plug the cable into the internal jack, and solder the wire ends to the external jack. Take caution to match the pins (refer to plug layout diagram if needed) This cable serves as the quick-disconnect patch cable, should you need to remove your stereo or take apart your dash in the future. Soldering directly without this patch cable could be a pain later if you ever need to remove the dash or stereo for repairs, etc.
When drilling in the dash, be very careful and know exactly what's behind your drill bit so you don't accidentally drill into something important!
On mine, I had a spacer/junk bin that was right below the radio. This made an excellent location to mount the external jack since it was inconspicuous and also I could wire it up at my workbench instead of in the car. Choose the location you like best to mount the jack. Push the jack through your hole you drilled and use the nut supplied with the jack to screw onto the jack and hold it in place.
Step 5: Test Your Connections & Reinstall the Radio.
I'd suggest a test run before you completely reinstall the stereo to find it doesn't work. Hook up the cables and give it a try. If everything sounds good, install the radio and put the dash back together.
Once it's all together, all you have to do is put the CD changer on your "silent" CD, put it on track repeat and use the MP3 player to pump the tunes.
You can see here's my setup with the jack installed. Sleek and WAY better than an FM transmitter.
Step 6: Burn Your Special "Silent" CD
Now, in order to play the audio from your MP3 player, we need to trick the CD changer into thinking it's playing a CD. The stereo doesn't know that the audio is really being supplied by your MP3 player instead of the CD changer.
In order to do this we just burn a special "silent" CD. It's got regular tracks, but there's no sound played. Download the 5 minute "silent" MP3 below and create a CD using your favorite CD burning software. I took the same file and added it multiple times to the CD so that I had many tracks. Just fill up the CD with these blank 5 minute tracks so even if you don't have the CD on repeat, you'll still hear nothing from the CD and everything from the MP3 player.
Once you've burned the CD, pop it in your changer, put it on repeat play, and you're all set. Turn on your MP3 player and test it out.
At a cost of under $10 and 1-2 hours (depending mostly on how easily you can get your radio out of the dash) it is well worth the great audio you'll now enjoy!