Tricking An Ancient Protocol To Play Tunes

A lot of technological milestones were reached in 2007. The first iPhone, for example, was released that January, and New Horizons passed Jupiter later on that year. But even with all of these amazing achievements, Volvo still wasn’t putting auxiliary inputs on the stereo systems in their cars. They did have antiquated ports in their head units though, and [Kalle] went about engineering this connector to accommodate an auxiliary input.

The connector in question is an 8-pin DIN in the back, which in the days of yore (almost eight years ago) would have been used for a CD changer. Since CDs are old news now, [Kalle] made use of this feature for the hack. The first hurdle was that the CD changer isn’t selectable from the menu unless the head unit confirms that there’s something there. [Kalle] used an Arduino Nano to fool the head unit by simulating the protocol that the CD changer would have used. From there, the left and right audio pins on the same connector were used to connect the auxiliary cable.

If you have a nearly-antique Volvo like [Kalle] that doesn’t have an aux input and you want to try something like this, the source code for the Arduino is available on the project page. Of course, if you don’t have a Volvo, there are many other ways to go about hacking an auxiliary input into various other devices, like an 80s boombox or the ribbon cable on a regular CD player. Things don’t always go smoothly, though, so there are a few nonstandard options as well.

32 thoughts on “Tricking An Ancient Protocol To Play Tunes

  1. I’m waiting for a stick with an optical encoder and a small laser diode via optical fiber.
    It would work like the old tape deck to headphone jack but instead of emulating a cassette it acts like a cd disc.
    Reading the position of the spindle and transmitting the right light pulses to the head sensor.
    That would be perhaps the craziest way to do it.

    1. That’s only going to work if you’ve got an external amp between head unit and speakers. Most vehicles have 4 speakers and most small mp3 type devices cannot drive large speakers directly – especially 4 of them.

    1. I am trying one of those to emulate a cd changer on an alpine car stereo (ai-net protocol) with mixed results: cannot pause, no titles, max 99 tracks per “cd” (6 cds max), seems to continuously run even when another source (radio, cd) is selected. Sometimes veeeery slow to start…

    1. My family never had a car newer than 10 years old. And my favorite was from 1976, When we bought it, it was 25 years old already. It’s obvious that author of this article believes that everything that’s not newest generation is ancient or/and obsolete.

    1. Because he wanted to retain functionality of the head unit. Going directly into the amp chip would work as long as the music source doesn’t overdrive or underdrive it. I hacked into the CD audio line input on mine and it still needs a CD in the drive to unmute the audio.

    1. Volvo has been slow to the market with technology, just like Toyota. Their newer cars are actually very nice, many upgraded standard features. The price hasn’t changed though… Too damn expensive.

  2. 2007 for a volvo is nothing.
    i suppose that is the joke.
    The older head units use a din for the aux amp and what is kind of like but not exactly a mini din for the cd changer.
    if you need to communicate with it to play why not pass button presses from the head unit to the player while you are at it?

  3. 2001 S80 T6 Volvo is the worst car I’ve ever owned. When it runs it’s great. Extremely hard to work on, overpriced parts, CAN bus is so proprietary it’s almost worthless, engineering is overthought and in my mind ill considered. (Eg. You can’t adjust the seat once you put the car in gear until after you have turned off the ignition and waited 10 minutes) Naturally my wife loves it.

    1. Every car I’ve ever owned has been Swedish, so my perspective might be skewed a bit, but my girlfriend’s 2004 S80 is actually pretty straightforward to work on. Then again, it’s a low pressure turbo 5cyl model so there’s less to go wrong in the first place (compared to your T6.) Most of my other cars have been SAABs, and Volvo’s engineering has been positively sane in comparison.

        1. I guess it depends on the fault but one can get a simple blinking (IIRC the engine check light) diagnostic triggered via the ignition/car key (again IIRC). IMHO the big problem with Saabs is that most are very easy to break into and hotwire making them attractive for criminals.

  4. Not sure about Volvo, but on my Toyota factory stereo I soldered a plug to the CD input with no other modifications. Put a CD in right side up and the CD operates normally. Put a CD in upside down and the CD is quiet but the amplifier remains active and the plug is enabled.

    1. In my winter beater fiesta i did similar but had to record a “silent” cd as the cd player only activated the amp when it detected a valid audio disk. Bmw was a bit easier, add aux in coding to the headinit, small bluetooth dongle recieving steeringwheel keypresses sniffed off the canbus and jobs a goodun :)

  5. The amount of effort spent rigging this up could have been used on just upgrading to a modern head unit. Prices have fallen and you can even get styles matched to the cars interior. If you want to splurge, you could add an android stereo head unit and play flappy bird while waiting in a parking lot. A modern head unit adds Bluetooth stereo, hands free, even popular music streaming services if you have access to cellular data that doesn’t rape you.

    1. Sometimes you just don’t want to upgrade the head unit because of the way it’s integrated into the car. For instance I have controls and headphone jacks in the passenger area of my van. It was way easier to add Bluetooth to my head unit then upgrade and hack everything else so these passenger controls would still work. Not to mention what Hackaday reader would want to install anything off the shelf when they can hack it? If you want off the shelf then go somewhere else my fine sir. Lol

  6. I want a device I can plug an SD card into and plug it in place of a CD changer like Ford used in the late 90’s and early 00’s. The 3rd generation Taurus only came with an in dash cassette in the stupid oval “football” head unit. Scoshe and Metra made rather ugly replacements to hold a 1DIN radio and the HVAC controls had to be transferred from the stock football.

    For the fancier models with the EATC (Electronic Automatic Temperature Control) there is no aftermarket option. A few have successfully hacked up their EATC football to put in a 1DIN radio. Some look decent, some look horrendous. A simple plug and play device to connect in the trunk would be ideal for the EATC Taurus. Put 6 folders on the SD, each with 99 MP3 files. 594 songs ought to be plenty for most people, and it would be theft proof because nobody steals a Taurus football.

    There’s only a few million Fords, Lincolns and Mercurys that were made with the option of the 6 disc CD changer, which few buyers opted to add to the list. The wiring is there in all the vehicles. Mountaineers and Explorers would need some cutting done on the console bin liner since that’s where they put the changer. Probably the same for other Ford trucks with the changer option.

    Unfortunately the only CD changer emulator for Fords works with the *next model* of changer ready radios Ford used.

    If only the 6 disc in-dash changer in my 2002 Sport Trac could be upgraded to read MP3 off CD-Rs…

  7. Rather cool this. I used to just solder straight to the output amp and put an 1/8″ connector on a blank bit of panel. This is not so easy, but you do not have to open the radio to do it.

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