HOW TO ADD TOSLINK DIGITAL OUTPUT TO YOUR CD PLAYER FOR LESS THEN $6

Here I will do my best to show you how to add a Toslink optical digital output to just about any head unit with a cd player or even a DVD player in it. After some research I first thought I was missing something. It looked SO easy to do I was wondering why companies did not add it to more units. Just to made sure I had the concept right I modified an old Eclipse deck but that deck had the option of a digital output so I thought that might be why it was so darn easy to do. Now I have an Alpine 7995 and compete in SQ comps. I also use Alpines 701 processor that has digital and analog inputs but without digital outs from the HU I was using the analog signal piped through the IA-Net. This was OK but not perfect. On IASCAs zero bit track there was a fair amount of noise with the volume at max. This is not good in SQ comps. So, being a poor working guy like everyone else I wanted  the clean clear signal that digital would provide but could not afford a new HU with digital outs. So I figured I would just see if I could add a Toslink digital output to my head unit. Its pretty easy if you have even basic skills, a little time to research the chips used in your HU and a little creativity. On this page I will tell how to do it to an Alpine 7995 but I will tell you what to look for to do it to just about any HU. I will not waste time telling you how to take your HU apart as everyone will be a little different.

First a little background on what Toslink is. Basically its a way to transmit data digitally from one point to another. There are three main parts: transmitter (TX), receiver (RX), and a fiber optic cable between the two. The TX uses a special LED to transmit the digital signal via light waves. Those light waves then travel over the fiber optic cable to the RX. The RX then take the light waves and changes it back the digital electrical signal. The advantages using this method is that sense there is no direct electrical connection between the two points there is not way to pick up other electrical noise along the way. In a car this is a big advantage with all the noise going on. Of course you get all the other advantages of a clean digital signal.

Now in the case of audio a standard called CP-1201 is used for the digital signal. This is important when you are looking to a Toslink TX to use for this project as well as finding the right point to tap into your HU to get the right signal (more on that later). There a quit a few companies that make Toslink TXs and each have a range of models. Here I am only going to talk about the ones made for audio. To be sure that the one you are looking to use or you are looking for is the right one that is for audio. You can use websites like THIS ONE  to look up the part number and get the data sheet that will tell you all about the part. If you are looking for some place to order these parts www.digikey.com is one of the best places. Bellow is a typical description for a Toslink TX found on the datasheet. If the one you are looking at does not say that it conforms to the CP-1201 standard then it will not work for this project.

Now that we have an idea which Toslink TXs will work its time to look closer at it and how its going to be wired up. There are a few different variations to the basic design but below are the two main standards. These standards are ones that does not use a shutter and the ones that do use a shutter. The advantage of using a shutter in the TX is to allow higher data transfer, up to 15mds.

Toslink TX that don't use a shutter is shown below. It usually has 5 pins, three that are used for electrical connection and two that are used to secure the TX to the board. As you can see there is only one part needed to make this work, a capacitor.

The second type are ones that use a shutter. These usually use 6 pins, four for electrical connection and two to secure the TX to the board. As you can see there is only one part needed to make this work, a resistor.

So here are a few things to look for when picking a TX. First make sure its using the CP-1201 standard. Next, and one of the most important would to operating voltage. I have yet to find one that will work directly from 12 volts and there probably is not one. The two main options are 3.3 volts and 5 volts. From my experience its a lot easier to find 5v  inside the HU then it is to find 3.3v. Now make sure it has a decent data transfer. They usually rage from 5-15mbs. I used a 12.8mbs with no problem. I would get the highest one you can find. The last thing that may be a factor it the transmission distance, in other words how far it can transmit the light through the cable to the RX. This can range from 2-10 meters. Just be sure the TX you get has enough range. Below is what this info will look like on a data sheet.

Now on to the fun part, making this work. First you need to take your HU apart, all apart. Take the CD transport (the part that actually plays the CDs) completely out and then remove the main board. Of course............<add in any and all cautions and removal from liability, LOL.

The first thing we are going to do is find the CP-1201 standard digital signal we need to run the Toslink TX. Its not that hard to find. The first way to do this is to actually look around of the boards and see if you see a point labeled "DOUT". I know that some units are nice enough to have a test point, labeled and all, that you can tap into for the signal. My Eclipse had this on the main board. I know an Alpine 9851 has it on the transport board. Take some time and look around on both board for it. The writing its nice and small so you will state looking crosseyed after awhile, LOL. This will make your life much easier if you find it but of course my Alpine did not have this. If its not there then you have to find which chip is outputting the CP-1201 signal. The easiest way to do this is to simple look up each of the chips on www.datasheetcatalog.net and see what each chip does. As you look up each chip make a note of what it does. If you cant find a chip just move onto the next one and see if one of the others is what you are looking for. On my Alpine its was the TC94A14FA chip. Below is part of the pin functions of a chip from the data sheet. As you can see this chips pin 4 is where the CP-1201 comes out. This is what you are looking for but it might not be on the same pin # of this chip. Also note that the same chip usually has the digital to analog converters. Do not mistake this for the MP3/WMA decoding chip that is usually separate.

 Once you have found the right chip and pin you can do one of two things. The first one would be to soldier a wire straight to the chips pin for the DOUT. This wire would then go to the Toslink TX INPUT pin. The bad thing about this is one; you would have a wire connecting the CD transport and the main board all the time and two; you would have to soldier straight to the chip. I have a really nice Pace devac soldering stations and pretty darn good soldiering skills so this would not be a big deal for me but for most people it would probably be the end of their HU. Next option would be to trace that pins path until it gets to a component. It much every to soldier to a component pad then to the chip. This option is better but you still have the wire between the board and transport. The best option is to trace the pin all the way to the main board. Its really not that had using a DVM. Just set it to measure resistance, put one prode on the DOUT pin and then follow the trace around the board till it gets to the plug going to the main board using the other prode to verify your still following the right trace. The trace might go to the other side of the board through a small throughhole in the board so watch out for that. Once you have gotten to the plug mark which pin it is. Now on the main board plug find the corresponding pin and mark it. If you want to make doubly sure you have the right pin plug the transport back into the main board and again with your DVM verify you have the right pin. At this point you have two options. The first one is to simply solder a wire to the back side of the plug. Again, the pins are pretty close together so it can be a challenge. Or you can see if that pin goes anywhere on the main board and if it does find an easier spot to soldier the wire too. On my HU that pin actually goes no where. I even unsoldered the plug in order to look under it to verify that it did not go anywhere, it was just a pad with no traces coming from it. Because of this I had to just solder straight to the back of the plug as shown below.

Next is finding a new home for the Toslink TX. This is really up to you and your HU. On my Alpine there was a spot that was made for some other type of plug on other models but on this model it was blank. It matched up pretty close to a hole on the back of the HU which was a bonus.

Because the Toslink TX had different pin locations on the bottom of it I had to drill a few new holes in the board in order to mount it to the board. This is easily done with a small drill bit, just be careful your not drilling through any traces on either side of the board. In the location I chose the top side of the board had no traces around it and the bottom had a nice big ground plain towards the front (pins 4-5 would be here to mount the TX)  and nothing where the three electrical hookup pins would be (pins 1-3). This worked out perfectly. After drilling the holes I turned the board over so I was looking at the bottom of the board. Around the holes drilled for pin 4 and 5 I then scraped off the coating around the holes to expose the copper underneath it. This is so that I could get a nice strong solder connection for those pins. I then mounted the TX in its new home using only pins 4 and 5 to hold it in. If you can not find a suitable place to mount the TX to the board you could always just turn it upsidedown, glue it to the board or case then wire it up. There really is not reason why other options would not work as long as it will work.

Now its time to wire this little bad boy up. Your Toslink TX might be slightly different then what mine is so make sure you look at the datasheet for your TX for proper hookup and added parts. For the TX I used pin1 was ground so I simply jumped from pin 1 over to pin 4 that was soldered to the ground plain. It then needed to see around 5volts on pin 2, VCC. It just so happed that right next to where I mounted the TX there was a nice big 5volt trace, it was even labeled "5V", so I jumped over to that for VCC. When you do this look around on the board for the same thing. There is a pretty good chance you will find a test piont that will be labeled "5v". If you cant find it look for something labeled "VCC" and I am sure you will find that. It is more then likely around 5 volts to power other ICs on the board and should work just fine for what wee need. Warning - do not use anything labeled "VDD" as this is usually around 8volts. For pin 3 you simply connect the wire you soldiered elsewhere that goes to the "DOUT" to that pin. Now you have to add the additional parts, whatever the datasheet calls for your TX. The one I used simply used a 0.1uF cap between pins 1 and 2. For this I used a very small SMD cap that fit right between the pins. For added strength I used a little shoe glue around the TX base just to make sure it was not going to come off. Guess what, that it, its done, complete, finished. Now that was easy wasn't it. Well OK, your not quit done yet but its should work at this point but not try it just yet.

The final step is to cut out or modify an opening for the TX on the case of your HU. Again where I mounted the TX there was already a hole for whatever plug goes to on other models. All I had to do was dremel it out a little bit and I was done. You might have to be a little bit more creative.

Now just reassemble everything and you now have a HU with optical digital outs....if you did everything right. You might want to make sure its working before putting everything back together. An easy way to test it is if you have something like a soundcard in your PC or a home audio receiver that has Toslink inputs, use a power supply to power the HU and test to make sure everything is working. Keep in mind that the tuner will only use the analog outputs but the CD will not use both analog and the new digital out.

GOOD NEW - mine worked perfectly the first time on the test bench. I run the digital to my soundcard to verify it was working. Wow, now I had digital outs to run to my 701 processor and I could not be more happy about that and the fact that I did not have to spend big money for it. So lets look at the cost. The TX itself is at most $5, few cents for the cap, few cents for the wire and solder = comes out to less then $6

NOW FOR THE BAD NEW - If you are planning to use this on an Alpine AI-Net HU and the 701 processor then this is for you. If not then there is no bad news. OK, with the 701 hooked up to an Alpine HU using the AI-Net the 701 will not switch to digital like it does with HUs that come with digital puts. As many might already know if you have a 701 already, if the 701 is being used with a AI-Net HU and it does not have digital outs it will not even give you the options to change. That option is not even in the menu. I thought that maybe it was because Alpine HUs that come with digital outs turn off the analog signal through the AI-Net and the 701 would see this and switch to digital. So I disconnected the analog signal going down the AI-Net cable but that did not work. If you hook up the 701 in stand alone mode it works fine but I really wanted to use the HU to control volume and sublevel. I even tried to store that setting with the right digital input selected, put the 701 back in AI-Net control mode, then reload that preset in hopes that it would select the right digital input but that did not work. Basically I am thinking this: the 701 was made to work in one of two ways. The first one would be using AI-Net gear, HU, Changer, DVD player but it will only except AI-Net gear for digital inputs. It must send some type of signal to the 701 letting it know whether eaach unit does or does not have digital outs and only then allows you the option of changing the inputs. The other way is to run it as a stand alone unit and then you can select any of the 3 analog and 3 digital inputs. Running it this way you have to use the controllers volume, balance, fade and sub level control.

I am still working on a way around this and if anyone has any input please feel free to email me at Turboegt@aol.com

I hope you enjoyed this little project and if you have any questions or comments feel free to email me.