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Thread: Looking for help w/ modifying OEM headunit as input device.

  1. #1
    Variable Bitrate silencery's Avatar
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    Looking for help w/ modifying OEM headunit as input device.

    First off, let me apologize for the upcoming long post. If anyone can help, I'd really appreciate it!

    So here's what I've got so far:
    - Serial-port interface to command the carputer.
    - Hacked up oem headunit to utilize as buttons on interface.

    Unfortunately, my experience in getting the custom button interface hasn't been very positive. The custom controller i built works, however, when wiring it up to the headunit's PCB, everything seems to go crazy.

    If i use my input device to make a connection on one side of the switch and another to a ground trace, it signals a connection; even when the switch is in the open position. What's strange of course, is that the multimeter reports everything correctly; a deactivated switch is dead and vice-versa, only when I try applying my custom interface do the buttons start behaving strangely.

    Another situation which is just as bad is when I try to use the rotary (knob) switches. When I make a connection direct to the switch and not through the PCB, it will read an input correctly. However, no matter which combination of connections are made, the switch cannot differentiate between a clockwise or counter-clockwise turn. Effectively, this means I can only utilize one function of the switch instead of the two I was hoping for (clockwise vs. counter-clockwise).

    Is there something I'm missing here? The rotary switches are manufactured by Alps. While their website is quite helpful, I can't seem to find a datasheet on the particular switches I'm working with, so I'm basically flying blind. Is there a particular way to test w/ the multimeter to check rotational orientation?

    Admittedly, I'm pretty noob when it comes to working w/ PCBs, but I can solder and I'm a pretty quick learner. If anyone can possibly offer any wisdom or point me out to some references, i'd be truly grateful.

    Thanks!

    For reference, I'm attaching some images of the PCB itself. The headunit was taken from a 2004 Toyota mr-s and is a pretty standard Toyota headunit. Warning, large pics!

    PCB 1
    PCB 2

  2. #2
    Variable Bitrate
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    I might be missing the point a little here, but could any of the microprocessors that are still attached to the board, be interfering with the signals?

    I would solder the outputs from the switches straight to your controller card, and then cut the tracks coming from the switches, to ensure they arent going anywhere else...

  3. #3
    Variable Bitrate silencery's Avatar
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    Dominik, thanks for chiming in.

    Quote Originally Posted by Dominik
    I might be missing the point a little here, but could any of the microprocessors that are still attached to the board, be interfering with the signals?
    yeah, that's what I was unsure of. Frankly, I have very rudimentary knowledge of the board, so I'm just making guesses.

    I'm thinking about soldering direct to the contact points on the switches, but I'd rather not since it might affect they way they work (i'd have to solder directly on top of the patch). If I have no other alternatives, I suppose that's what I'll end up doing.

    Any other ideas?

  4. #4
    Constant Bitrate
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    What sort of serial interface are you using here ?

    the LC75804 chp that you have looks like it is a "1/3, 1/4 Duty LCD Display Drivers with Key Input Function"

    The rest of this is all guesses based on a different HU that I have taken apart so it could all be wrong for your HU.

    Do the keys use a matrix instead of a common ground?

    Are you using an analog input or a digital input for the rotary (knob) switches? what do they need ? have you checked the resistence to see if it changes as you turn them? what all functions does your normal HU control thru the rotary switches ? can you push them in ? can you pull them out ? do they rotate in either of those positions ?

    If I had to guess I would say they can be at least pushed in and when you push them in it connects the two pins on the outside. Turning them would use the three pins on the inside. voltage, resistance, and ground ?

  5. #5
    Variable Bitrate silencery's Avatar
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    mox,

    Yeah, you're absolutely right. I'm kicking myself for not googling that earlier. Looks like this will turn out to be more complicated than I originally thought.

    It seems to me that they're all using a common ground, but then again, I'm a n00b, so I might be mistaken. I have tried using several ground points though, and they always yield the same results. Any suggestions or tricks on how I can check precisely?

    After doing more research, I realized that the knobs might not in fact be switches at all. Alps, the switch company, makes something called an encoder which looks fairly similar to the knobs on the board; I'm assuming encoders utilize a complex combination of signals to differentiate, perhaps like a pot?

    The left knob on the HU is assigned to volume and the one on the right does tuning for radio stations. Both of them are nearly identical except the tuning knob clicks while the volume one does not. They can both be pushed in and they can both turn both directions infinitely. Since they do not have any stops on them, I originally assumed they were standard switches.

    I did try to take measurements on the rotary switches w/ my multimeter, but admittedly, I'm not quite sure what I'm looking for. Can I trouble you to point me in the right direction?

    I think your guess is accurate, at least that's what I guessed too. When you push a switch down, the two pins on the outside activate. If the three pins on the inside are in fact voltage, resistance and ground though, would you have any suggestions on how I could possibly utilize them to differentiate between left and right? I've tried several wiring combinations with no luck; both directions i try always register a signal.

    I really appreciate your help!

  6. #6
    Constant Bitrate
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    It sounds like they are encoders not what I was thinking about. I would try to find the information on encoders. Look at sites like this
    http://www.ubasics.com/adam/electron...rotryenc.shtml
    http://www.mcmanis.com/chuck/robotic...uadratrak.html

    I would first check and see if you can find the encoder that you have on the alps site so you can get the datasheet for it so you will know how to read it.

    For the switches I would trace back each and make sure you have one side on all the switches that is going to ground.

    I am including a quick diagram of the back of my radio panel (hand drawn) so you can see what I am working with as far as switches goes. On mine the second row where you see all the letters is where the traces go to. The SWxxx is the switch number printed on the board. and the letters by it are what pin on the second row I traced it back to.

    What are you using on your serial port to connect the switches? I am still trying to figure out what to use for mine and am looking for suggestions. I am thinking about using the I-Pac like many arcade cabinets use but am looking for other suggestions.

    It is hard for me to try to trace yours back from the picture since your uses both sides it look like to go wherever they and up going.
    Attached Images Attached Images  

  7. #7
    Variable Bitrate silencery's Avatar
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    wow, sweet! Thanks for the links. I've been googling for good rotary encoder links for the past 1/2 hour... haha.

    The interface I built was actually taken from a really old thread here. Here's a link to it: http://www.modasylum.com/guides.php?guide=21. The controller is really basic and easy to build. I'll post pictures of mine eventually, but if you visit the originator's site (the russian link on page 3 or 4), you can see lots of examples that people have built.

    I intend to just use girder to manipulate the applications I'll be using. In theory, i think it'll work for me, but unfortunately, I won't know until I get everything together...

    Let me know what you eventually come up w/; your project sounds promising.

    You're right about the tracks. They're incredibly hard to trace, and I have the board in front of me!)(!@)

  8. #8
    Constant Bitrate
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    Thanks for the link. I guess I'll be running out to the rat shack in the morning and picking up a few things.

    With my tracks I just went from one solder bump to the next checking the continuity. If the multimeter beeps I know I am still on the right track. This enabled me to track them all the way back to where they come onto the board. I would just start with one side of one and write down where you track it to (start calling it some letter) like I have in that hand written mess above.

    I have used girder before but I might end up using my own custom VB app to get everything I want to work correctly.

    It looks like yours end up going back to that controller chip so unless you can figure out how to control the controller chip you might have to diable it somehow in there.

  9. #9
    Constant Bitrate blackpacu's Avatar
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    hey, Im doign the same thing but with a ford focus headunit
    Basically I took the back circut board out for the buttons and made my own, its more like a contact board for each side

    The boards are some left over plexiglass that i had lying around with wires streched(parrallel to each other) over were the buttons would go. since my HU had rubber pads w/ a mettalic foot where the button is, the button pressing will short the 2 wires on the plexi and close the circut.

    Ill take some pictures and post them with in a day to show what I mean.

    Im replacing the LCD in the head unit with a graphical one from matrix oribital, GLK12232-25-SM
    It has an onboard keypad interface which im goign to hook up all the buttons to. Right now im using LCDC to control the keyinput in winamp and to do a few other things,

    I later plan to add led to light it up once i get everythign working good.

    good info on the encoder, i was planning on taking the one off the circut board for the radio to use but may just buy a new one instead since i would be able to get all the specs.
    amd 1700, biostar m7ncg 400, hitachi deskstar 120 8mb , 512 pc2700, liliput 7"
    now to put it all together

  10. #10
    Variable Bitrate silencery's Avatar
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    yeah, that's a good idea mox. I appreciate all the help. I'll just hafta be more patient and see what all my options are I suppose. Almost makes me wish I were an EE major in college instead... haha

    Blackpacu, your idea sounds pretty good. Please post when you get the chance. My original intent was to keep the existing PCB so I could utilitze the stock lighting but now it looks less and less probable.

    The encoder seems like an interesting device, but I think what you're looking for might a rotary switch. If you happen to know how to use the encoder, I'd love to hear it!

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