How to modify your car stereo for Bluetooth or Aux-In | Hacker Day

2021-11-24 03:53:42 By : Ms. Mandy Guo

If you are a tasteful car enthusiast, then you will not be able to bear the idea of ​​installing a rudimentary after-sales speaker in your beautiful, clean ride. A flashy modern host may ruin the appearance of a car's interior, especially if the car is retro, classic or retro.

Therefore, we will study how to modify your existing car audio to accept auxiliary cable inputs and even Bluetooth modules. In this way, you can effortlessly play the latest music from your smartphone while still maintaining the original look on the dashboard.

Depending on the audio player you choose, you may prefer the 3.5mm auxiliary jack, or if your smartphone no longer has a headphone port, you may want to use Bluetooth audio. No matter which method you use, the process of modifying stereo is roughly the same. In order to achieve your goal, you need to find a way to inject audio signals into the host amplifier stage while ensuring that no other audio sources are also sent there.

It does not matter whether the audio source is a 3.5 mm jack or a Bluetooth module. The only difference is that in the latter case, you need to buy a Bluetooth module and hardwire it to the auxiliary input you created, while also splicing the module into the stereo power supply. In the case of a simple headphone jack input, you only need to connect the auxiliary cable or 3.5 mm jack to where you can reach, and you are done.

Of course, this guide will not cover all stereo speakers in the sun. There are edge cases, and depending on the specifics of how your original car radio works, these exact methods may or may not work for you. However, this guide aims to give you a conceptual thinking about how such mods are done so that you can investigate the hardware in front of you and make your own decisions on how to integrate external audio inputs that suit your use case.

If you have something very retro, this hack can indeed be very simple. This usually applies to radio/tape players from the 1970s and early 1980s, which have an analog volume knob on the front. In this case, the audio signal flows directly to the amplifier through the volume knob. Some kind of basic switching determines whether the radio or cassette signal reaches the volume knob and then passes to the amplifier section and speakers.

Therefore, you can stitch your own audio on these devices in a variety of ways. The easiest way is to cut off the stereo audio traces or wires leading to the volume knob and connect them to the DPDT toggle switch. Connect the wires of the volume knob to the two pins in the middle of the switch, and connect the original stereo feed to the pair of pins on one side. You can then connect the new auxiliary wire or Bluetooth input to other pins on the toggle switch. Then toggle the switch to choose between standard operation or external feed. Install the switch in a clean and tidy place, and the job is complete!

Or, you may find a button on the deck that can switch the radio to cassette tape mode whether or not a tape is inserted. In this case, you can connect the auxiliary audio to the audio output of the cassette module, and then just use the existing switch on the deck to select the cassette mode. Since there is no tape in the deck to provide the signal, only your external audio will pass through the volume knob and then be transmitted to the speakers. Simpler and cleaner!

In the digital age, things have become more complicated. This refers to the host computer controlled by the digital display and buttons, and the microcontroller runs the entire program. Interestingly, many radios in the 1980s and 1990s used simple 4-bit microcontrollers that were just enough to run a simple mainframe and might be cheaper than the more common 8-bit parts. Basically, if you have an LCD on your 80s or 90s stereo, this part of the guide may be for you.

Numerically controlled decks usually use a chip called a multiplexer or multiplexer to determine which signal to send to the amplifier. A multiplexer is basically a chip with multiple inputs and a single output. The main microcontroller in the host usually controls the multiplexer chip by switching several GPIO pins or using serial, SPI, I2C or other interfaces. For example, when the user presses the button of the FM radio, the microcontroller will send a signal to tell the multiplexer to route the FM radio input to the output of the amplifier. If they press the tape button, the microcontroller will instruct the multiplexer to route out the tape audio.

Therefore, by controlling the multiplexer, you can control the audio reaching the amplifier and speakers. Depending on the multiplexer chip used and how well it integrates with other hardware in the stereo, this may be easy or quite difficult.

Most multiplexers will be variants of the 4051/4052 series. For example, an early 90s stereo using Hitachi HD14052BP multiplexer can be easily modified by auxiliary input; just flip a few pins to change the multiplexer input. Therefore, with a properly wired switch, you can tell the multiplexer to select the tape or CD input even if there is no tape or CD. Simply connect your auxiliary inputs to these same pins and you can start business.

However, more modern stereo speakers can be difficult. Generally, multiplexers are integrated into more complex chips that handle multiple functions. To make the multiplexer switch inputs, it is usually necessary to use a silent audio CD, or to command these chips through an interface such as I2C, serial, or SPI. This is the primary job of connecting auxiliary inputs to tape, CD, or other audio input subsystems.

For example, the Mercedes Audio 10 CD audio host produced by Alpine in the late 1990s uses Philips TEA688OH signal processor IC. The chip handles volume, treble and bass control, and certain radio signal processing tasks, while also acting as a multiplexer.

Connecting the auxiliary input to the CD input is very simple, but it is more difficult to actually switch the stereo to that input. Many people choose to simply burn an audio CD with silent tracks that last an hour. Inserting it into the deck will select the CD input, and the auxiliary audio can be played on the silent output of the CD itself. However, this is an indecent solution that requires the user to carry the disc to switch to the auxiliary mode, which also means that the mechanical disc player must remain in working condition.

In this case, a more elegant solution is to force TEA688OH to switch to the CD input or other input, regardless of whether there is a CD in the drive. This is very possible because the chip receives signals from the main microcontroller via I2C, which are listed in the chip's data sheet. However, it needs to add an Arduino or similar device that can use I2C, a DPDT relay, and some supporting components.

The I2C line between the stereo microcontroller and TEA688OH signal processor must be cut off and connected to the relay. Under the command of Arduino, the relay usually routes the signal from the stock microcontroller to the signal processor so that the volume and other functions can be controlled normally.

However, if the user wants to switch to the auxiliary input connected to the CD input, they only need to press the button connected to the Arduino. Then the Arduino flips the DPDT relay and connects its own I2C interface to the signal processor. Then, you can send a command to switch the input through I2C, and then restore the control to the standard microcontroller, thereby restoring normal functions such as volume control.

Obviously, the latter case is much more difficult and requires knowledge about the use of microcontrollers and I2C communication. However, the end result is much more elegant, with just the push of a button, the device can switch to auxiliary input. Although the examples given are for a specific Mercedes head unit, other OEM speakers of that era used similar components and could be modified in a similar way. Just find a way to pipe the auxiliary input to the amplifier section through the on-board multiplexer.

Sometimes, you are lucky, a simple additional input is already hung on the back of the standard stereo. Normally, stock stereos have CD changer input, so this option can be easily added to the car without replacing basic audio equipment. These inputs usually come with analog audio inputs and even power supplies. A basic method is used to determine whether a CD changer is connected. In the case of Kenwood standard CD changer input, it is as simple as connecting a pin to another pin through a resistor. The host can switch to the CD changer input, and audio can be input through a pipe.

However, others are more complicated. Certain luxury cars in the late 1990s used optical digital audio input, which was difficult to deceive with off-the-shelf hardware. In addition, some hosts use serial or other communication methods to control the CD changer and will not switch to input unless they receive the correct message from the hardware. If you don’t have a CD changer, it’s also difficult to figure out how to spoof this kind of communication.

However, if you can make it work, this is a good way. Generally, it allows intrusion of custom inputs without turning on the stereo. For decades, old-school car audio hackers have been doing this on cars like the Mazda Miata, swapping their own audio inputs without destroying the elegant appearance of the original dashboard layout.

In general, to hack the auxiliary audio input (whether it is Bluetooth or other means), all you need to do is send the signal to the amplifier, not any other signal. If you can figure out how to route signals from the various sub-components of the host (such as CD players, tape drives, and radio modules), then you should be able to figure out how to route your own signals. Hope this guide helps explain the basic process required so that you can figure out how to hack any stereo. Good luck, if you have completed a particularly good hack, send it to the prompt line. have fun!

In most cases, only a good Bluetooth speaker in the back seat sounds much better than a normal system. Simple and modern solution. The only problem is that you need to turn on/off the speakers every time you turn on/off the car. Sony has a series of car-mounted walkman CD players. The player is controlled by the car's power supply. When you turn on/off the ignition and continue playing, the player will automatically turn on/off. Someone only needs to make a power controller BT speaker with playback recovery function.

Why do I say that? I have a Volkswagen Eurovan and I gave up to make the sound better. :)

Most car stereos are powered by an ignition switch power supply, so you can find this line and use it to switch the relay that powers the speakers. On British cars, the wiring is green or white with pink stripes. (Because you can use either, the latter is preferred.)

This was true in Australia at least 20 years ago, but most of the more modern cars in the world are at least permanently turned on, and the host is turned on/off via CAN bus commands.

Chrysler (at least since 2008) hosts also switch inputs via CAN. The public and I are pretty sure that the same is true of SAAB at the turn of the century. Many others I suspect these are just the ones I have played

I'm not sure if "most" is accurate. The loose bluetooth speaker at the back is better than the a4 channel system specially designed for vehicle volume... Is it possible to play music easily in the space, of course. But nothing more.

I think I’m a bit lucky. My 2003 Volkswagen Jetta radio has a connector on the back, which can be connected to the above-mentioned optional 6-disc CD changer in the trunk.

I bought an eBay part for $14, made specifically for that compatible Audi audio, and it tricked the audio host to play it from the CD changer. This part ends in the auxiliary jack, which I cleanly installed on the virtual panel on the dashboard. Like I said, I think I get out of the car easily.

By the way, I'm sorry to reply to you directly, I don't know how this happened!

I had some success on the AM/FM/CD of the Dodge factory host in the mid-2000s. All controls are digital, used for volume/tone/FR-LR balance, etc. The output of the CD transmission is serial numbers, uh. All ICs have OEM labels-no data sheet. I connected a 4PDT relay to the power amplifier and switched between my hacking and normal operation, which is not terrible. I put an operational amplifier between the headphone output of the phone and the power amplifier, which allows me to control the volume through the phone. The lack of tone control/FR-LR balance is tolerable. I got what I wanted-the ability to play music from my phone.

I used a 4-bit multiplexer between the cd transmitter of my Audi mmi plus system and the motherboard, and it was connected to the i2s line. The rpi zero is connected and the gpio line is used to control the multiplexer. rpi zero runs mpd, so the music is played in the car instead of being streamed and decomposed via Bluetooth. If you want but don't bother, you may be able to set rpi zero as a Bluetooth receiver. The smartphone is just a remote control.

If modern digital decks are difficult to crack, is it easier to provide an amplifier module and splice it into the speaker wire?

I have a USB-AUX adapter similar to this in my 2003 CRV. It plugs into the CD changer port.

When I first drove, I did this on the deck of my Renault Clio. The CD transmitter is on its own board, with a ribbon cable for control/power and a 5-pin cable, which seems to use only 3-pin (L/R/Gnd). Splice a jack into it, then insert an old Dension iPod adapter bracket (use engine power to start/stop the iPod), and insert a CD with a 74-minute blank track in the deck.

About 20 years ago, I bought Delco digital tuning car radios. They are very good radios. One cassette recorder is missing. It is easy to find the 4-pin connector, so I have an auxiliary input.

But other than that, they have no volume control, and you can splice in the input. Control the processing of DC to IC. So for others, I had to splice cables between the tuner board and another board.

I have a 2004 Jaguar that uses a fiber optic system called D2B (formerly MOST). This is a challenge, but managed to reverse engineer a solution that simulates a CD changer. Add RPi and get a complete Bluetooth solution.

I sold some online, but now the cars are too old and there are not many requests to come in, so I stopped making them.

From 2000 to 2003, D2B was also used in some Mercedes-Benz cars. Strangely, they decided to use different plugs for fiber optic cables, but the rest are very similar.

Well, my solution provides much lower fidelity, but wins with convenience:

Thanks! I read this article over and over again, wondering why no one recommends a simple FM (or AM, I guess) Bluetooth->FM transmitter. Over the years, I have had a lot of bad cars, which is always the first choice. Yes, this is not CD quality, but if you think that Bluetooth will not recompress your audio and is at least as bad, then I have some bad news for you...

I really like audio fidelity, and you can usually get a lot of compression through noise artifacts or faded instrument volume. In other words, the Bluetooth FM transmitters I have tried (such as this one) are usually enough so that I can still enjoy music.

I did this on my fifth-generation Honda a few years ago. It has a CD changer, but no auxiliary input. (Bluetooth audio was not a real thing at the time) But I can use my MP3 player directly through the headphone jack output.

I cracked a signal through the 6-disc CD changer line, and then only played a special "silent" CD, so the host was happy to accept audio from the pirated auxiliary input.

Check out my teaching article here:

Coincidentally, yesterday I upgraded my car stereo with one of those cheap $5 Bluetooth/mp3/usb/sd_card/fm_radio panels connected to the amplifier and power supply. The biggest problem is to decouple the panel module from the power supply, because it will input a lot of noise to the amplifier. When you power the Bluetooth module and the amplifier from the same source, this always seems to be an issue with Bluetooth audio because these modules are very noisy. This has happened to all the Bluetooth modules I have used before, and even commercial headsets often have problems, but this time it is another problem. Some large 2200u and 3300u low esr capacitors, dc-dc isolation converters must be used, and even a low-noise regulator must be used.

A simple and non-intrusive way to connect to a cassette tape player is to use a cassette tape head for input. In the past, the cassette I used had a standard jack cable extending from the side to assist in my car audio. Until now, I am sure that someone will make a tape with an internal Bluetooth module, powered by the mechanical force applied by one of the drums when it rotates in playback mode.

When I was still driving, I used one of the cassette tape auxiliary adapters, but I found that it was still affected by the tape hiss, even without the actual tape. I think that when converting magnetic signals into audio, the head is just rubbish. In the 1990s, it was better than nothing, but it was not good by any standard.

Why go through all of this, because most new smartphones don’t have a 3.5mm headphone port?

If you have a degree in electrical engineering, you can take apart the car stereo and add auxiliary inputs. To be honest, this is both skill and time intensive. Who has the time? This seems to be a lot of work, but the return is very small. There are better ways to play/stream smartphone music through old car radios.

Speaking of car audio systems. The most important thing is sound quality. If this OEM sound system modification is not done correctly, you will end up hearing a harsh hum, hiss, or static noise, which will drive you crazy.

Bluetooth FM transmitters were a popular choice for vehicles with dual noise in the 80s and 90s. However, for 2000s cars equipped with more modern D2B systems or integrated navigation and infotainment systems. Doesn't work. Most Bluetooth FM transmitters are affected by ground loop noise because most of them are connected to a cigarette lighter to supply power.

You need to find an FM transmitter, which is not powered by the same power source as the car. It will play excellent sound quality like magic. Gizmo Guy has a great new product. This is a simple iPhone adapter that plugs into your iPhone and allows you to stream all iPhone music through any car radio. It is even suitable for cars with fiber optic sound D2B systems. No need to replace or modify any parts of old cars/classic cars. Just plug the Gizmo Guy gadget into your phone and set up your radio, and you can play and stream all your music directly through your stock audio system.

Hard-wired FM modulators are both versatile and easier than anything in this article.

I have a 2005 Toyota Tacoma. The CD player stops working. I have used several different FM modulators for a while. Never liked the quality of music. So I pulled out the radio/CD player and turned it on. I found where the signal from the CD player enters the amplifier. I soldered a 3.5mm stereo plug to it and cut the cable to the CD player. Connect it to my MP3 player. I should take the time to install a resistor for the CD presentation signal. I didn't think of it until I reinstalled everything. I just hung a CD upside down in the device and it still works well today. Almost the same thing was done with the 2001 Corolla which had only radio and tape player. It is easier on the corolla because the unit has a connector for an external CD player. Do this 5 years ago or more.

Given that Crutchfield has some simpler options, I saw a 08 Hyundai Accent, which has a dashboard system that is close to the factory appearance. However, the 2 x 12-inch subwoofer may slightly ruin this illusion. A long time ago, a friend owned 62 Volvo 544s with sleeper systems. The bad 70s audio system will start...and then do nothing. He will open the glove box, which is filled with a nice (even now) system, hidden from any inadvertent sight, used for easily stolen equipment. The 6×9 and 6-inch door speakers do a good job of LOUD, but the tune is good.

Does anyone want to talk about article art? It may be a potential hacker attack. Imagine a tape drive, but it is used to receive a phone call (maybe an internal USB or audio jack, or even an internal RFID, it will trigger the automatic connection of the phone to the car’s Bluetooth and play music). I might just do it myself.

I have thought of this, which would be great, but it would prevent access to the phone to select music or navigation.

Many Fords (at least in my experience-Carnival, Focus, Mondeo, Fusion, and Transit Vans) have additional costs when buying and installing Bluetooth devices or accessories. Therefore, it exposes the pins on the back of the radio to the auxiliary/Bluetooth audio. You can find many pre-crimped stereo jack cables with single-pin connectors on eBay. These connectors only plug into the main connector and have a 3.5 mm jack at the end. The Bluetooth function requires some engineering input of the module present on the board or in the alternate firmware or the panel/canbus (I don’t remember which is needed) but in most cases, switching to Bluetooth mode will switch the output to auxiliary L/input R anyway .

I just want a CD changer simulator for Ford cars from the late 90s to the 00s. I can insert an SD card with six folders, each containing up to 99 MP3 files. Use the head unit CD controller to operate it. No one stole the "football" from the 1997 Taurus sprint.

For classic cars from 2000-2008 with telephone or satellite (Sirius) hardware, there are two other simple input options. I did this for the 2007 Passat/Audi this weekend, it has a Sirius box and no AUX option. If you do not use satellites, it is easy to splice into the audio input at the output connector of the Sirius box. Then select the satellite on the console to get your AUX input. Also for the older SAAB, I used the phone input option. Connect an AUX connector to this connector and a switch to switch the phone option to ground. "Phone" is written on the console, covering the radio/CD.

Great article, but a bit beyond my imagination. I have a transport truck using can-bus guessing so I don’t want to take out the radio. I would like bt but to me it all looks very complicated.. I want to pre-outs rca though. Will it be easy to solder in pairs before the signal enters the amplifier? Will the sound quality be better than running a converter on an amplified speaker line? For those who can play switching, great article and great information...

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