The Folly Of Adding An Auxiliary Audio Input To A Hyundai Sonata

Why auxiliary audio inputs haven’t been standard on automotive head units for decades is beyond us. But you can bet that if you’re looking at a low-priced sedan you’ll need to buy an entire upgrade package just to get an audio jack on the dash. [Jon W’s] Hyundai Sonata didn’t have that bells-and-whistles upgrade so he decided to pop his stereo out and add his own aux port.

A big portion of this hack is just getting the head unit out of the dash. This is made difficult on purpose as an anti-theft feature, but [Jon’s] judicious use of a butter knife seemed to do the trick. He lost some small bits along the way which were recovered with a Shish Kebab skewer with double-stick tape on the end.

With the head unit out, he opened the case and plied his professional Electrical Engineering skills to adding the input. Well, he meant to, but it turns out there’s no magic bullet here. The setup inside the unit offered no easy way to solder up an input that would work. Having done all of the disassembly he wasn’t going to let it go to waste. [Jon] grabbed a nice FM transmitter setup. He wired it up inside the dash and mounted the interface parts in the glove box as seen here.

It’s nice to know we’re not the only ones who sometimes fail at achieving our seemingly simple hacking goals. At least [Jon] was able to rally and end up with the functionality he was looking for.

48 thoughts on “The Folly Of Adding An Auxiliary Audio Input To A Hyundai Sonata

  1. Sucks, doesn’t it?

    On my old car, the only aux in was via a disc changer option. But you couldn’t just wire something into the audio line, there. Oh no. That would be too easy. The headset had to think that the disc changer was actually installed, and this required some nonsense init commands over RS485…. I ended up just buying the damned box that did it for me for $70. It was cold out, and I didn’t want to be dicking around with a scope, laptop and dev board in my car.

  2. After checking out all the silliness people go through to get aux inputs on Subaru Outbacks, I bypassed it all and got a Parrot bluetooth hands free kit that can also play audio through bluetooth, a mini jack, iPod connector, or USB jack. It sounds and works better than I ever could have imagined, and was under $200 for the Parrot unit (MKi9100) and harness. There are special wiring harnesses for just about any car, including for a 2007 Sonata. I don’t know why more people don’t go this route– it’s amazing.

    1. So you are asking, on a hacking site, why don’t more people buy expensive new devices instead of trying to modify existing ones?

      This is one of the instances where something seems like it should be extremely easy to do, and at one time would have been, but modern car stereos aren’t cooperative. Its sad to say, but in the end it would probably be best to just buy a cheap aftermarket with an input and modify that to your liking if need be.

      1. It’s a great hack and appropriate for this site, for sure, but there’s no end of they-deliberately-make-it-hard-or-too-expensive posts about car stereo setups and it’s just not! It’s actually really really easy to bypass the head unit on just about any car with a relatively cheap bunch of gear.

      1. Not necessarily… there’s a nifty device from scosche (or any other generic brand) that takes the high voltage speaker level and drops it to line level that the bose needs… unless the bose uses a digital signal, in which case yea, you’re pretty screwed.

      2. Or if you have a nicer deck with 5v preouts, you could just use the harness adapter that lets you send that signal to the amps. (I used a Metra 70-7551) My deck only has 3v preouts, so it’s a little quiet, but I paid less than 25 bucks in parts (including a new harness for the deck), so I can’t complain. Just make sure you have at least 4 preouts for the amp.

      3. RE: speaker to Bose adapters, there exist digital conversion versions of the same boxes Abbot speaks of. They generally cost 1.5 to twice as much, but if you are dead set on feeding an aftermarket stereo’s sound to the digital factory amp it can be done.

    1. My car’s OEM stereo has roughly half of the logic components for the computer that controls the car’s engine, brakes, lights, everything… Almost every single part of the car ties into the stereo somehow. Oh, and as I found out when some guy hit my door panel, the stupid thing kills everything if any one component is missing (ie. passenger door speaker).

      Replacing it means I have to either:

      a. Move the existing stereo AND it’s speakers (or maybe just a few resistors ?) somewhere roomy like the trunk, running all the wires to it. THEN install a new stereo in tandem.

      b. Buy a $2700 aftermarket computer unit and rip out the OEM computer. This is a $13,000 car.

      c. Hack the stupid stereo.

      That’s why I hacked mine.

      1. There should be a law that prevents manufactures from integrating the entertainment system with other functions it’s just piss poor engineering on their part.
        Also what model of car is it so I can avoid buying one.

      2. I just ripped my OEM stereo out and got a third party one that had USB,SD, and Aux in etc since it controlled no other vehicle functions.
        The Hyundai seems to have separate climate controls etc like all cars should so that would have been an option for it.

  3. Had a Ford Focus 2000 that I wired an “AUX” port to the OEM stereo. Guess I was lucky because my circuit board had good labeling. Basically I opened up the stereo, found something along the lines of “L” and “R” going from the CD player to the main circuit board, soldered on a female stereo connector cable, drilled a hole in the front plastic of my stereo, and epoxied on the stereo connector. The labeling could have been on the CD player circuit board but I can’t remember.

    To be able to hear anything, I made a CD with 70 minutes of recorded silence and just played the CD. In terms of sound it worked pretty well. I grew up playing violin so my ears might be a bit more sensitive, but I couldn’t stand the loss of audio quality going through a FM transmitter. I did have to fix it once because some jerk tried to steal it and pried on the front plastic, breaking my hack.

    I do like how he put it to the glove box tho, having a dangling wire in front of the stereo makes things slightly more messy.

    1. For my Chev, I found a spot for a jumper next to the input on the back for an optional CD changer. Short it and audio from the input gets processed (no matter whether the screen says it’s on FM/AM/CD), remove the jumper and the stereo behaves as normal.

      One toggle switch and a female jack later, and the only concern I ever have is accidentally overdriving the stereo by forgetting to set the volume low on my MP3 player before I hook it up.

    2. I did exactly the same thing back in university with the (obviously not stock) CD player in my ’87 Dodge Aries. I found some traces on the board that appeared to connect the CD’s output to the amplifier, and converted the RCA line out jacks on the back of the thing to RCA line ins. I also discovered fairly quickly that it only worked when a CD was playing, and also make myself a blank disc. It was an ugly-ass hack, but it seemed fitting for an ugly-ass car.

    3. a similar thing is quite well-documented on the ’95-’99 nissan maxima..i posted this last time there was an aux input hack but it got no love so i’m posting it again :P

      turns out the nokia cable does a poor job conducting sound..i soldered it all together with some solid-core 22ga and the sound was much better than from a tape deck adapter.

      the microphone worked perfectly. the little remote let me pick up / hang up calls and control playback. it was a great setup but i sold the car. got a bluetooth / usb stereo in the current car (toyota mr2 :D).

  4. Adding an FM modulator is far from a hack, hackaday! If that is a hack then installing a head unit must be the mother of all car hacks, and that is just a basic install of equipment. You can buy a new head unit, with aux in, that will sound worlds better then stock for $69 now. For $99 you can get one that has USB for better sound quality+charging that will allow you to time align your speakers, tune it with EQ and setup crossovers so you don’t start sending 20hz to a 6.5″ speaker. Hell, Sony now has one that will work with Android, Blackberry and iPhone. Making your car interface will all smartphones, now that is quite a hack.

    IMO anyone who drives more then 30min. to work each day should really consider upgrading their system. In a year you have spent roughly 260 hours (10 days) listening to music in your car. That doesn’t even include time driving that isn’t going to work.

    MobileWill there are multiple ways of dealing with the Bose system in cars. You can interface into it(requires some skill but doable buy a higher end shop). You can remove the head unit and amp while keeping the speakers (this requires the amp to be replaced with a different one that can handle 2 ohm drivers and possibly a custom crossover or two). You can replace it all, which will always sound way better then any Bose system (just like you did).

    *rant mode off, Sorry if that was a bit rant like but when you have worked with car audio, and realize how much real hacking goes on in cars it is frustrating to see this get recognition.

    1. I agree it’s not exactly a hack more like what you have to do if ripping out the stock stereo is not an option due to it being a non standard size or the car being so poorly designed it controls other functions.
      Though on this vehicle it appears to just be a standard double DIN and is just a stereo the only hard part would be finding a custom face plate or modding the old one so the replacement does not look ghetto.

  5. Yeah, aftermarket is for the win here. There is, however, a third solution not mentioned. FM Modulators have the advantage over FM Transmitters, but still definitely not as good as a real input. Audivox is one of the better brands of modulators I know of.

      1. +1 for older vehicles. Rusty, ugly, mostly-dependable, lovable old cars and trucks! :)

        Don’t get me wrong, I love (most) modern automotive technology, but sometimes I think the ‘evil corporate hands’ of the industry have meddled too much. Should I blame the accountants or the business management people? lol They can’t tell me there wasn’t an engineer somewhere in the place whom asked, “hey, doesn’t it suck that there’s no auxiliary audio input?”

        +1 for Jon W putting the input jack elegantly into the glove box. *golf clap*

  6. I was able to get near wired quality with my FM transmitter by soldering a 3.5mm jack to the internal antenna and then soldering a 3.5mm plug to a small telescoping antenna I found (I think it was for a TV card I got with my old HP laptop). It violated FCC standards (range was up to 100 ft), but the quality was great. Ultimately though, the charger for that FM transmitter went bad, so I wound up adding an aux input to my Pioneer stereo.

    1. No, you weren’t. The loss of quality is inherent in the FM process; it basically applies a bandpass filter to the audio from 50-15000Hz (so you lose a bit on each side a priori) and then there’s the whole pre-emphasis thing making things messy (receivers should theoretically take care of this… but you’re still bending the audio in unnecessary ways.)

      The quality problem with FM isn’t due to reception issues; it’s due to the way FM works. So even if you had an impedance-matched transmission line going from your modulator to your antenna input, you’re still degrading the audio by subjecting it to the FM process.

  7. Aftermarket won’t always work… think of all the cars these days with anti-theft features in the radios where the car won’t run without the proper radio in there.

    Sad that he had no choice other than an FM transmitter… they suck HARD. Unfortunately, I am in the same boat with my Subaru Forester. I was thinking about doing the trace on the PCB hack to my WeatherBand channel (useless anyway!), but I just don’t know deeply enough into electronics to manage something that extensive.

    1. New cars won’t even start with a non-factory radio? Really? I can see this as an anti-theft feature but there is no way for the owner to turn this feature off?

      This seems like it should be an anti-trust issue as it would completely destroy the aftermarket market.

      1. He’s wrong. Cars have anti-theft systems where a stereo removed from a car won’t work in another car but there is no car with an anti-theft system that will disable the entire car.

      2. My Chev houses a lot of the logic components for the car itself on the same circuit board as the stereo. I can replace it with a $2700 aftermarket computer and any stereo I want, but it’s a cheap car and that makes little sense.

    2. There isn’t a single car that you can’t remove the radio on. The question is are you willing to spend the extra money for the proper harness or custom work. Misinformation like this is what has hurt the mobile electronics industry for years.

      1. There are lots of adapters and brackets. I have yet to own a car I couldn’t find what I needed to install aftermarket stereo without cutting the harness. Doesn’t cost much. Of course I do that work myself except for my first cat.

      2. The I seen the stereo run the heat and AC BMW’s infamous idrive comes to mind but never anywhere was it necessary for the car to run.
        such a car would end up being extremely unreliable

      3. Have a look at some older Subarus. My gf has an ’06 Outback; there is a reason CD-ribbon hacks proliferate the internet on these – the “head unit” comprises much of the dash functions, including the climate controls. You can’t just nip over to millionbuy and drop any old aftermarket radio in.

  8. Did this to a friend’s tape stereo a while back. Gutted the tape deck, soldered the “tape inserted” wires together, then soldered a left, right, and ground wire to the chip amp inside and an audio jack.

    Didn’t think it would work, but it was perfect.

  9. From time to time I bounce around the idea of putting a small MP3 player inside one of those adapters that look and fit like an audio cassette.
    But most cars don’t have cassette players anymore,
    (I do). Sure, I could just plug the MP3 player into one of those adapters, then the wire gets tangled around the shifter and such.

    1. They already make MP3 players that are made to be inserted into a standard cassette player. By monitoring the spindles, I believe they even respond to the fast forward and rewind controls built into the deck to change songs. A quick Google shows one at DealExtreme for just over $15…

  10. In Subaru hack there was some guidance in the printed circuit board, but you really don’t need them. Just find two traces from fm-receiver to electrolytic capasitors and bang, there you have a place to connect your audio source, just like in Subaru hack..

  11. It’s not post-apocalyptic messy, but it’s not real clean either.

    Still, it’s a hack; thus, bravo!

    If he would buy a KIA Forte for his next car, it would already have an input for his green cable, an iPod input (special features if used with special $35 cable that everyone got in the mail for free anyways) or directly off USB . Tried a 32GB USB drive in it, it works fine. My “Free 3-month trial” for SIRIUS lasted over six months, and when I didnt renew, was mailed offers as low as $18 a year for every channel…but it still sucks).

    Car would be cooler looking (for an import, anyways) :)

  12. I did this 1973 or so with my fathers Oldsmobile. Very easy,cut #3 wire at the volume control. Insert jack with NC to source. Plug in Norleco Carycorder,power from jack (no battery)too. Dad didn’t know it was there, till that long trip thru radio hell.
    Bluetooth audio conections are degraded. Mpee’s thru bluetooth? So much has been lost, it’s time to start over or find vintage gear and put it to use.
    The video-game gen has weaseled these screens onto the dash and into the very fabric of the car as heated seats. You have to LOOK at it to do any thing, including using the radio or other media thru it’s amp and speakers. If you have trouble?….
    Get an old jambox. Those white eggoid docks aren’t even up to an old jambox.
    Question where things are going. Build power amps and an EQ box for front end control, sans radio. Soon that phone will nag you with storm warnings etc. so you won’t miss the lack of live radio.

  13. I just did the same to my girlfriend’s ’98 Honda CRV. After managing to get the radio apart, I found the left and right audio lines from the enclosed FM module. I figured since her smartphone has an FM radio included, I’d just cut the trace and replace the FM module, rather than dishing out cash for the switched audio jacks. I simply followed the traces to 2 surface mount resistors, re-soldered them on their ends to break the line, and soldered an audio cable from an old pair of headphones to them and a nearby ground. Worked like a charm, though I also had to fix the broken rotary encoder in the volume knob by replacing some broken plastic with some shaped and baked clay. Didn’t pay a cent in the end, used only stuff I had on hand.

  14. I did something similar on my 93′ Celica SX, got all the way into the head unit only to find no aux input and an almost entirely bare of labels PCB… so instead I downloaded the schematics for the FM modulation chip used, traced the lines to find the left and right channel before the pre-amp, broke the lines and wired a switching 3.5mm headphone jack in place. VOILA!

    Now I have a stock standard looking head unit that changes from radio to AUX input by just plugging in any 3.5mm cable. Will have to put up a worklog for it…

  15. Hyundai = KIA = KILLED IN ACTION…it is a military term which the Koreans who built the car are all too familiar with. They claim it stands for, “Keep it Affordable”…but it comes from a country that doesn’t speak english.

    KuDoZ is right…no need for what you did; any stereo with a tape deck or CD player is easily hacked, with much better audio quality than you get from an FM adapter.

    Of course the “Life Hacker” solution would be to buy a better car for less money…but you already bought it…and no one in their right mind will buy a used KIA for the price of a used car from a good company.

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