Building an SPDIF/CAN to Line Out for Factory Headunit
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It really depends on how nicely finished people want it. If you just want a programmed circuit board with some heat shrink around it and wires/connectors hanging off then it would probably be ~$65. If you want a nice aluminum case and everything to look pretty then closer to $100. It also depends a lot on how many I need to build. If only a half dozen people have any interest then I will probably assembly them all by hand which is a pain but cheaper since having it assembled by machine is a bit pricey in lower quantities. If closer to 25 people want one (I am thinking the NAV people might have interest) then I would have the boards assembled since I don't want to solder 25 of them together. It could also be done as a kit for people who feel like soldering it. I bet that would be less than $50.
These are of course estimates. Basically, I am not going to make much of any money but the parts are not free and it will take a bit of time to assemble and program each one also. I am designing it for myself to use and I figured I would share the technology so long as I am not doing it at a net loss.
These are of course estimates. Basically, I am not going to make much of any money but the parts are not free and it will take a bit of time to assemble and program each one also. I am designing it for myself to use and I figured I would share the technology so long as I am not doing it at a net loss.
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Hell no man. Don't be afraid to make money on this. As long as your price aren't ridiculous they will sell. I went to school for that kind of stuff and I know what goes a long into producing something like that. It ain't easy to say the very least.
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OP, you must be an engineer or something cuz I have no idea what you are talking about. 
If I could dumb this down. You are making a device that will connect to the OEM radio which will allow the user to easily connect an after market amplifier without losing any of the functinaility of the OEM setup? This sounds too good to be true!! lol
Does this bypass the factory amp or use the signal coming out of the amp?
As for selling this I am very intersted. Hook up with Turbosocks cuz I want!!
If I could dumb this down. You are making a device that will connect to the OEM radio which will allow the user to easily connect an after market amplifier without losing any of the functinaility of the OEM setup? This sounds too good to be true!! lol
Does this bypass the factory amp or use the signal coming out of the amp?
As for selling this I am very intersted. Hook up with Turbosocks cuz I want!!
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To sum it up "for the rest of us" so to speak....OP, you must be an engineer or something cuz I have no idea what you are talking about.
If I could dumb this down. You are making a device that will connect to the OEM radio which will allow the user to easily connect an after market amplifier without losing any of the functinaility of the OEM setup? This sounds too good to be true!! lol
Does this bypass the factory amp or use the signal coming out of the amp?
As for selling this I am very intersted. Hook up with Turbosocks cuz I want!!
The box will allow you to eliminate the factory amp and add your own. He is overcoming 2 obstacles:
1. The audio signal from the amp is digital and unusable by conventional amps.
2. Even if you do convert that to a useable signal you lose volume control. So his box will also tap into the digital info that controls volume and possibly other parameters like fade, balance, etc.
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Want even more !!
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Gimme Gimme Gimme!
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Excellent summary Doc Holiday.
Right now I am in the making it work phase. The first version will only have volume control, but adding balance is not hard at all once volume control is working. It will only have a stereo output so there would be no point in fader. Most aftermarket radios have 3 sets of RCAs, Front, Rear, and Subwoofer all with left and right. This will only have 1 pair, just left and right. It is definitely possible (I will look at it after this is working) to build a box with front and rear outputs (2 sets of RCAs) that would use the fader control. Personally, I set the fader and balance (normally just the fader) and don't move them. So, what I would do to replace the entire amp system would be split the output of my box 3 ways, once for front, one for rear, and one for subwoofer to external amplifiers. Then set the gains of each of the amps/channels so get the fader/balance the way you want. Not as convenient but it would be basically the same.
As I stated previously I am waiting on the first boards to come in (probably a week and a half from now) then I can start writing software. Also, the output of this box will NOT be affected by bass, mid, or treble settings. Adding those controls is a lot more work and I probably won't do it at all since I don't want it anyway.
Right now I am in the making it work phase. The first version will only have volume control, but adding balance is not hard at all once volume control is working. It will only have a stereo output so there would be no point in fader. Most aftermarket radios have 3 sets of RCAs, Front, Rear, and Subwoofer all with left and right. This will only have 1 pair, just left and right. It is definitely possible (I will look at it after this is working) to build a box with front and rear outputs (2 sets of RCAs) that would use the fader control. Personally, I set the fader and balance (normally just the fader) and don't move them. So, what I would do to replace the entire amp system would be split the output of my box 3 ways, once for front, one for rear, and one for subwoofer to external amplifiers. Then set the gains of each of the amps/channels so get the fader/balance the way you want. Not as convenient but it would be basically the same.
As I stated previously I am waiting on the first boards to come in (probably a week and a half from now) then I can start writing software. Also, the output of this box will NOT be affected by bass, mid, or treble settings. Adding those controls is a lot more work and I probably won't do it at all since I don't want it anyway.
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The circuit boards are out for delivery. I am excited for this weekend. I doubt I will get as far as hooking it up to my car because I have a couple other projects to work on also. Hopefully I will get some of the code written so in about a week and a half I will have a working prototype.
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Good Luck, because I have no clue on the terms you are talking about lol.
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A quick update with a picture. Below is a picture of the blank board.
![SpdifBoardPic.jpg]()
WARNING: The following section is a bit technical. Reader discretion is advised.
I finished assembling one board yesterday and so far so good. The following is working:
1) SPDIF receiver
2) Power Supply
3) No magic smoke was released
The SPDIF receiver takes the audio from the car and turns it into a standard stream called I2S which can easily be converted to the analog audio we use all the time on RCA connectors. I still have the following to test:
1) Microcontroller
2) DAC
3) CAN transciever
4) Software to do the magic
The DAC takes the I2S (that I can now generate) and makes the analog audio that runs to amplifiers. The CAN transceiver is a simple level converted to make it so the Microcontroller can take in the CAN signal. The software is pretty simple but I am a bit rusty so I have to remember how to work with this microcontroller (PIC18).
With any luck I will have a demo video of something done by the end of this weekend. I will keep you posted.
WARNING: The following section is a bit technical. Reader discretion is advised.
I finished assembling one board yesterday and so far so good. The following is working:
1) SPDIF receiver
2) Power Supply
3) No magic smoke was released
The SPDIF receiver takes the audio from the car and turns it into a standard stream called I2S which can easily be converted to the analog audio we use all the time on RCA connectors. I still have the following to test:
1) Microcontroller
2) DAC
3) CAN transciever
4) Software to do the magic
The DAC takes the I2S (that I can now generate) and makes the analog audio that runs to amplifiers. The CAN transceiver is a simple level converted to make it so the Microcontroller can take in the CAN signal. The software is pretty simple but I am a bit rusty so I have to remember how to work with this microcontroller (PIC18).
With any luck I will have a demo video of something done by the end of this weekend. I will keep you posted.
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Great progress, man. I'm looking forward to reading your writeup on how it works out. I wonder if doing this would add any perceptible latency to the audio (I'd think not, but it's a question that came to mind). While latency doesn't much matter for music, it does matter for phone conversations.
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So, they must be doing something nearly the same as this inside of the factory DSP box, so I doubt the latency will be worse. Actually, it has a large chance of being better since this will do no actual DSP (not bass, treble or any kind of equalization) so I have a feeling it will be faster. I can measure it when I have it working and if it is enough to matter it would easily show up in the measurement.
Also, there is already about a second of lag in most phone calls, try calling somebody you are right next to some time. So, even if it adds a tenth of a second I doubt that would be much of an issue, unless you are using the factory amp also. In that case the two audio signals would not be sinked which would be bad.
Also, there is already about a second of lag in most phone calls, try calling somebody you are right next to some time. So, even if it adds a tenth of a second I doubt that would be much of an issue, unless you are using the factory amp also. In that case the two audio signals would not be sinked which would be bad.
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Alright, big update with good and bad news.
----Good----
Attached below is a picture of the prototype connected to the wiring harness of the DSP/Amp under the passanger seat. The conversion of the SPDIF to analog audio is working and I was able to listen to the music with no issues. I labeled the major components. There is no CAN connected yet, check the other section below for explanation. So the power comes from the harness and is switched with the ignition. The digital audio also comes from the harness. My board converts the digital audio to analog which runs to the RCA connectors at the top of the photo and can then be used as desired.
![20131031_205242.jpg]()
----BAD----
The head unit seems to freak out more than I though when you unplug the DSP/Amp. At first I thought my board was having issues because every 2 or 3 seconds the audio would cut out then come back in and it just kept doing this. When I connected the DSP/Amp back up it quit doing this. The head unit must be trying to talk with the DSP/Amp and resetting when it can not find it. I can work around this but it will take more time and work. For now things should work with the unit plugged in and just using this for expansion.
----Other----
I have not written the code yet to read the CAN bus so for now the volume is just set at maximum. This is not finished by any means this is just to test if I can convert the audio to analog correctly. I will be working on the CAN portion tomorrow and into the weekend and I will put up an update as soon as there is volume control.
Once I have volume control working I will make a video with some speakers connected to the output so people can hear it working.
----Good----
Attached below is a picture of the prototype connected to the wiring harness of the DSP/Amp under the passanger seat. The conversion of the SPDIF to analog audio is working and I was able to listen to the music with no issues. I labeled the major components. There is no CAN connected yet, check the other section below for explanation. So the power comes from the harness and is switched with the ignition. The digital audio also comes from the harness. My board converts the digital audio to analog which runs to the RCA connectors at the top of the photo and can then be used as desired.
----BAD----
The head unit seems to freak out more than I though when you unplug the DSP/Amp. At first I thought my board was having issues because every 2 or 3 seconds the audio would cut out then come back in and it just kept doing this. When I connected the DSP/Amp back up it quit doing this. The head unit must be trying to talk with the DSP/Amp and resetting when it can not find it. I can work around this but it will take more time and work. For now things should work with the unit plugged in and just using this for expansion.
----Other----
I have not written the code yet to read the CAN bus so for now the volume is just set at maximum. This is not finished by any means this is just to test if I can convert the audio to analog correctly. I will be working on the CAN portion tomorrow and into the weekend and I will put up an update as soon as there is volume control.
Once I have volume control working I will make a video with some speakers connected to the output so people can hear it working.
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I'm liking the expandability of it currently .. hooking up a sub the right way is win enough lol
.. hooking up a sub the right way is win enough lol
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CAN bus is working!!!! I was able to watch the volume number that my board is getting change from 2 to 10 as I turned the volume knob. So, it should be no problem this weekend to take that number and change the gain of the DAC and it will all be working. The CAN bus was definitely the hardest part, mostly because I have never used CAN on a PIC microcontroller so I was just being an idiot about setting it up. Anyway, expect a video showing how it all works by the end of the weekend.
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