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Playing music from a USB stick on a non USB car stereo? Answered

I have a Jeep Grand Cherokee with a multichanger CD and cassette but it won't play MP3 files. 

Has anyone any experience of hacking it so it can take a usb stick?


they make a fm transmitter that plugs in your 12v outlet in your car that has a usb port on it and plays mp3s. Here is a link to one on amazon there are several different ones to pick from. This one is under 10 bucks. Seems like the easiest way to go. http://www.amazon.com/August-CR100-Wireless-Transmitter-Control/dp/B001MQ0ROU/ref=sr_1_9?ie=UTF8&qid=1375240107&sr=8-9&keywords=usb+fm+transmitter

Thanks --- this easy to do ordering soon --- I will post how good it works ---

I agree with GADGETMAN. I used one of those for 2 years in an office where the radio had no external input. I just put a couple hundred songs on an sd card. I set the unit to transmit on 87.5 or something like that JUST BELOW the fm band. Of course, your receiver must be able to tune that also. That got the unit out of the FM band where it is very crowded here in a large city and made the audio much clearer with no interference.

A few comments before going to my answer...

I have used both cassette adapters and FM transmitters for quite some time, with varying degrees of success. The cassette adapters have been the most reliable and with a good tape head, quite clear and HiFi. Most auto tape decks have pitiful response, or if they supposedly have good response, may need to be cleaned and degaussed. My auto decks have been blessed with excellent response, hence my pleasure with using them.

The FM transmitters suffer from drift, unless you spend decent money on a good one. I have never heard one sound as bad as you say (AM quality, which would be about 100-4000 Hz). The last one I bought was from a 5 Below and works well as long as you keep a signal to it - otherwise it shuts off. Not sure if you have a similar store over there.

Now to my answer.
Get a MP3 player, that way it will be guaranteed to work right off the bat. If you want to hack into the wires, figure out which GND is signal GND, and then clip the LEFT, RIGHT and GND. Place a 3PDT switch (All Electronics has some, but I don't know if they ship over the pond) in there so you can keep the CD player functional (switch between sources). Obviously, you'd connect the wires to the stereo to the middle tabs, the CD player wires to one set of end tabs and the other end tabs would be connected to a MP3 player. Here's the catch, though, you wire a dual-ganged (stereo) potentiometer (probably around 10Kohm) as a voltage divider, to help attenuate the levels and give a better impedance match (most MP3 player headphone outputs are 32-64 ohms, while the CD player is most likely in the 10's of thousands of ohms). Wire one side of the "pots" to signal and the other to GND and take your signal out from the wiper, or center terminal.

To set the level, find what volume sounds good via headphones first and take note of that. Next set the pots all the way to GND. Turn on the MP3 player and push play. Turn the pots toward signal, switching between the MP3 player and CD player. When the levels sound about the same, put a dab of glue on the shaft and you are good to go.

You now have approximated the input level of the CD player on the MP3 player, installed a switch to go between 2 sources on 1 input, and added some extra impedance to your MP3 player's output/input, helping to keep the car stereo happy.

Good luck,

Is the multi-disk changer external? If so how does it wire into the stereo? Is it possible to hack into the input for the changer?

Already seen that thanks but will not ship to UK!

Oh sorry about that. Sometimes us colonists don't think about such things

Never mind, you're forgiven!

Apparently if the 'technology' is shipped abroad people like me may be able to hack it and turn it into something Home Land Security have to worry about. It does make you rather wonder if it's the inmates who are running the asylum now ...

Yes the inmates are definitely running the asylum. Unfortunately the "sane" people are so terribly outnumbered that it looks like they are the abnormal ones.

Some countries start out as penal colonies and turn into countries. Some countries turn into something of a penal colony.

It is indeed an external unit and I'd have no problem in principal binning it.

I have found the connections to it. They are:
1 - Audio out right
2 - Shield
3 - PCI Bus
4 - Ignition switch output
5 - Audio out left
6 - GND
7 - GND
8 - B+

I'm guessing that I'd somehow have to interpret the PCI bus to understand stuff like enable/disable, disc up/down, track up/down, and somehow read track info.

My problem is I've no idea how to!

A simpler solution may be to get an actual stand alone MP3 player and get a 3mm to 3mm stereo connection wire rather than the usb stick. Then you could wire a 3mm stereo jack in parallel at the head unit and surface mount the jack next to the stereo head unit. All control for play, stop, next, etc. would be done with the MP3 player.

You would have to make sure when you splice into audio left and audio right you wire them to the 3mm jack properly or your left and right may be swapped. Another thing I didn't consider is that the left and right audio may be looking for low level signals. You may have to have the volume nearly all the way down on the MP3 player.

Good point that's another thing to consider. I usually just go off and do these things half blind not considering consequences. I guess the question would be, if you threw caution to the wind and just did it, what is the worst that could happen?

Blow the input of the Stereo!

Now that would spell trouble as my 'ultimate authority' would have something to say if she had no music but our rubbish radio to listen to!

Aah yes. The ultimate authority. I understand completely. I don't attempt to "surgically alter" anything my wife may even remotely be affected by or lay claim to.

Thanks people but I have tried both already. As correctly identified, the tape adapter output is dismal and frequency response even worse - I've tried two different makes.

As you've also identified the FM transmitter is not very good either. What I found was continual frequency drift in the transmitter. Again I've tried two.

Get one of those tape adapters. Cheaper than a transmitter, more reliable and clearer sound. It's a cassette that goes into your tape deck and gives you a headphone jack to connect to your MP3 player.

Problem with the transmitter is there low power and short range. Often the reception isn't very good and it's like your listening to an AM station.