Adding An Input To An Old Head Unit

Tape decks in cars? Yes, that used to be quite common before optical media took over road. [Nirav Patel’s] 2004 Toyota Corolla had a deck that he used with a tape adapter in order to listen to music from his iPhone. But one day something happened and, although the adapter still worked, the cassette player started making distracting noises. [Nirav] set out to quiet the noise and install an auxiliary audio input for the sound system. There were some tripping points along the way, like breaking everything and starting a small fire, but perseverance got him to his goal. Because these units are built with compatibility for things like CD changers they have a communications bus called AVC-Lan. This protocol has been sniffed out and documented, and [Nirav] even found an existing audio-input hack that he based his design around. Now he’s able to plug directly into the dash and ditch the cassette adapter.

We’ve seen [Nirav’s] work a few times before. He’s shown us a first person shooter controller and his site was a resource in our Launchpad programming with Linux post.

[via Make]

38 thoughts on “Adding An Input To An Old Head Unit

  1. I dont want to bash the value of a hack, but when I worked in a car audio WD we were selling very basic jensen cd players for like 12 bucks retail, and yes they had an aux in on the front

    props for doing it, but I would not have

  2. Box stores often have $50 DIN sized CD players with AUX inputs right on the faceplate. Or many have standard RCA inputs which allow a simple mod to add a 3mm jack to the dash.

    In the case of some cars like the 03 Ford Tuarus its not that easy since it doesn’t use a normal DIN (1 or 2) head unit. You have to buy an $80 add on module to pretend to be a CD changer. In this case a cheap mod would be worth it.

  3. Reminds me of my first hardware hack…

    The first radio I ever had when I was 8 or 9 years old was a tiny hand held battery powered AM receiver. Then I got a record player from a neighbor who thought it was broken. I found out it was just a wire that had come off a prong in the power plug: my first ever electric repair.

    The neighbor soldered the signal wire into the radio, injecting the signal right before the volume control (the record player didn’t need a preamp). All I had to do to listen to a record (i.e. one of my dad’s old 45’s) was tune away from a station so the radio didn’t interfere, and start the record player. And remember to turn the radio off afterwards of course to prevent the battery from dying :-)

    Good times!

  4. I 2nd questioning the value of this hack considering the price of new mp3 playing decks with aux built in. I bought a new Sony one a year ago with usb as well as aux for $100. Im sure you could pickup a second hand one off ebay with mp3 for next to nothing. Dont get me wrong, i’m not saying this hack isnt bad in anyway. It looks to be very well done so kudos to Nirav. Its just the overall point of it fails me.

    1. Peter… A $100 car stereo/head unit might satisfy you. For myself, I have about $600 invested in a high quality pioneer CD unit that still functions perfectly and has awesome sound quality. I, like many others, simply aren’t willing to toss that sort of money out simply because it’s now a little out of date. Nor do I have the money to replace it at this time. So a hack is the best way to go. I’ve done a couple of older car stereos, two tape decks and a CD unit. Also, for someone who has a vehicle they wish to keep original, whether it newer or a vintage, hacks like this are an invaluable way of doing that. It enables you to add an auxiliary input without compromising the vehicles original look. There’s businesses who specialise in repairing and upgrading classic/vintage radios to accept an external input. There’s are some very valid reasons. Another is simply for something to do. Yet another is to save a working piece of audio tech from going into landfill.

    2. This hack is very useful for someone who has reason for not wanting to just replace the head unit. My motorcycle has an AM/FM , Cassette, CB unit, with handlebar controls, and outputs for helmet speakers/microphone. If I were to change my head unit, I would lose all of these features. It is also not a regular DIN size, so nothing else will fit anyway.
      This hack allows retaining all factory features and controls, but I can now use any MP3 player as a source.

  5. Well for those that don’t see the value in this hack, try having a jeep wrangler. When the top is off the last thing I want is someone snagging my cd player and probably causing more damage to the dash bezel etc. I did this to my radio a while ago. Thieves will steal even the crappiest aftermarket headunit.

  6. We hack because we can.

    Sometimes it’s worth the money, sometimes it is not. Sometimes it is for something that doesn’t already exist. Sometimes it is not. Sometimes it is about reusing what you already have and sometimes it is just for the fun and experience.

    DIY hacking is R&D for the end user. Try some constructive criticism HaD community.

    Personally, I’ve done a very similiar hack and I’m glad to say that a) I did it b) I used stuff I already had c) one less thing in the landfill.

    Find, reuse, hack, upcycle. Rinse and repeat.


  7. There is no value to this hack ,, but aren’t people missing the point ?
    Hacking is as much an adventure and trying things out than anything else.
    Lets face it 80% of the maker stuff is intrinsically just junk to anyone but the makers crowd.

    Just from the image all of the stuff there to me is complete junk and a waste of time ,money (except maybe R2D2 but even then only as a toy).

    I am sure the people who made them would disagree vehemently , to them it was worth doing just for doings sake.

    Yeah you can get a £20 head unit with an aux in but where’s the fun in that ?
    “Here you are Mr HiFi dealer here is a 20”
    reply:-“Here you are here’s your head unit”
    “Oh that was fun for 20 seconds”

    Jac Goudsmit has the right idea , why hook up a radio to a record player and not just and amp. Simple because a radio was lying around and because you can.

  8. I did something similar 17 years ago to hook my CD player into a deck that only had tape.

    I agree with Sp`ange & Mav, Sometimes the hack’s value is just because it was something to do besides sitting around the TV or video games. And bandwidth is cheap for a few pics and commentary. If you find no value in it, skip it. I often find value in hacks that I’ll never get around to myself, but I often enjoy seeing how someone overcame an problem. Some people like putting together 1000 piece puzzles, I find tearing into something is my own “puzzle”.

  9. Did this many years ago — minus having to worry about audio network protocols — to add CD player input to an 8-Track. Yup, and 8-Track. Buddy had a late 60s car, and a new stereo in it just didn’t look right, what with all the chrome and shiny shiny. My only serious challenge was finding the Goldilocks spot along the audio path for the headphone-out level.

    I’d like to do something like this for my current ride, but I haven’t found anyone who has hacked the Nissan bus already. But I suppose sniffing the protocol would be an interesting exercise, sure to bring derision upon myself — unless I used an Arduino, of course.

  10. My dad used to do this sort of thing when I was a kid. He’s a retired auto mechanic and electrician. Except he used to spend hours making mixtapes for himself on cassettes, so he plugged his Walkman into my car that already had a CD player.

  11. I also did this with the tape deck in my old Daewoo Matiz. However, I used a much simpler approach, by cutting the output traces of the tape preamplifier and connecting a 3.5mm jack instead. Also used a button that jumpered the “tape inserted” switch inside. All mounted in the cassette hole (I didn’t need it anymore)

    Sadly the engine broke, but thankfully my new car already has an Aux input.

  12. I am also tired of the “this has been done already” or “I did this already” comments. Just keep it to your self if you are not impressed. This is a forum for sharing and ENCOURAGING creative efforts. Leave off the negative stuff and add some interesting observations if you have any creative juice in your bitter little bodies.

  13. “I am also tired of the “this has been done already” or “I did this already” comments. Just keep it to your self if you are not impressed. This is a forum for sharing and ENCOURAGING creative efforts.”

    exactly they are SHARING how they, or someone else did it, and what is wrong with that?

  14. lol, this is amazing i did a similar hack last week! :)

    what i did is much simpler i just removed the cassette system and put a female jack where the sound from the cassette sys connected to the mainboard of the radio
    then short circuited a switch that was on the cassette sys that was for informing the radio that there is a cassette playing
    so now the radio if you press the button for cassette it just waits your input from the jack :D

  15. this is good for those of us with cars from 1989 w/ original stereos. though it would probably be more difficult to do to my car. So, a good starting point for 20-year-old head units maybe :P

  16. Now that you have FM submitter on your phones such as N900 this doesn’t make a lot of sense but the fact is that most of the decks/cd players in cars doesn’t have input jacks.

    Even tho many FM radios can’t lock on the signal by your phone.

  17. Lol, this brings back memories.
    I did the same thing almost 10 years ago with an old aftermarket CD player.. (seems fairly common!) I needed an aux input to plug in my hacked/overclocked I-Opener (remember those?!) turned in-car-computer. After datasheeting all the guts, I got lucky.. The radio had a Phillips mixer chip in it, it determined which input was sent to the amp, controlled by i2c. So after wiring some RCA’s up to an unused input on the chip, making an I2C interface via parallel port, it was ready to roll. It didn’t matter what mode the radio was in (am/fm/cd) when you sent the ‘override’ i2c command, the mixer chip would just swap inputs. I made a little winamp plugin that sent the i2c command over LPT port automatically when you played a song. It worked, and it didn’t cost anything! (I could barely afford gas, wasn’t going to blow it on a stupid 300$ radio with aux input)

    Those always looking for value here constantly should probably head straight to overstock/woot/buy/monoprice/ebay and delete their HAD bookmark. (you’d do those here who enjoy reading tales of human ingenuity a big favor)

  18. I’ve used the same method as samnmax on my own units before CD ones were of achievable price for a student.

    Possibly the most common hardware hack in the world?!

    While those looking for value are possibly misguided, there’s some sense in saving your hacking potential for things that you can’t buy for a fiver and using it on bigger, better stuff.

  19. If it works out for the hacker then it has value…DUH?

    Who let all the tight-assed non-hacking spirited whining douchebags into my hack a day?

    It’s like there’s a contest to see who can out douche each other.

  20. This hack, or a similar method to add an aux in to an existing headunit, is essential to maintain the stock look in a car. Buying a $35 Sony XPLOD will also add an aux in to your car, but will it look like it belongs there?

  21. or you could have tapped into the tape deck signal out from the tap head amp board witch is where the auto reverse switching is done.

    if you are not up to voiding the warranty and core value (that’s right car radios too get returned to factory for refurbishment) you could get the cassette adaptor and cut off the ear phone plug and replace the connector with a different connector for other devices.

  22. Pioneer headunits with a cd changer input can use the player input as a aux input. You just have to make a 3 pin plug thats floating around on the internet. After that you have to power the unit on by hoding the function key. after it powers on its in a setting menu, that has some weird stuff in it, but also a aux:off mention. Change it to aux:on and you have aux input :)

  23. i like this…i went to pick n pull and got a kenwood excelon from 1998 a kdc-ps655 or something and it had only a cassette player under the faceplate…the cassette adapter or the unit made loud circling noises, plus fidelity is questionable from cassette adapters, right? or do recording engineers sometimes transfer stuff recorded straight to digital back to tape to “warm it up a bit” …its a preference thing, yes. however, the cassette noise and a quest for higher fidelity leads me to want to open it up and solder. using the cd changer input is apparently a no go because unit is circa 1988, exactly one year before the 13 pin din would change to allow and adapter like the cac1ax or something to to make the 13 pin din become and aux input…ugh. ( i even tried to avoid buying that adapter cable putting a 10k ohm resistor between pins 1 and 9, and the audio leads to 8 and 12, audio ground to 6….but again, one year to vintage on this deck for that to work. so i’ll probably solder into the cassette feed on the board.

    anyway, i got that kenwood excelon for about $24 a pick n pull plus their stupid environmental fee bs. these heads sold for about $250 back in 1998 e so yeah i could buy a $65-100 unit from walmart that has usb and or a aux in and maybe hd ready or whatever…but lets look closer in terms of what i need and what i get for the money. what is important. is the thd on the head and the signal to noise ratio important? (the excelon had a 56 without dolby and 65db with dolby on). modern kenwood decks with a usb and aux input have a 70db snr. not much improvement there. such a modern deck i s$90 on amazon. maybe i should even be using the decks amp so the snr and thd don’t matter? or do they still contribute to fidelity somehow when sending a signal to a nicer outboard amp (like the nakamichi i got from a junker lexus ls400, one you only got if you added on the $5k upgrade package of sunroof heated seats and nakamichi system or whatever)? also, isn’t there a chance an older cassette head unit has separate crossover control (?NON fader crossover or something?) for front and rear channels? wouldn’t that be useful especially if your amp doesn’t or you don’t want to get crossover networks? maybe the older excelon has indepent subwoofer control whereas the new sony xplod others tout by virtue of a simple aux in has pretty much nothing in terms of eq or audio controls (likely a simple left right front back fading/panning ability and one or two lame eq presets). and some of these new units aren’t thought out very well, it takes 6 button presses to get to a commonly used menu. i dont know if i am wasting my time or not but i would bet you i learned a ton more in my trials and tribs over this than some doosh who just got hisself that pionerr for 165 smackers at best buy.

  24. This guy did great. Did you notice that he included a three pin header so that he could repair the signal wires should they ever get damaged? PURE GENIUS. I would rather team with an open minded farmer and a tool box than an engineer with hindsite and a podium.

  25. I didn’t read every comment but props to hackers because if you have an old school clean 80’s car and want a head unit that matches and also don’t want to settle for less than the best possible sound quality/functionality this is the stuff you gotta explore

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