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Thread: Tracing the leads on my 2005 Accord head unit

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    Tracing the leads on my 2005 Accord head unit

    I'm just starting up this thread to track my progress with tracing the leads on my head unit main board. I'm isolating the climate controls so I need to verify which components it goes through and, if possible, see about mimicking the LCD as a pair of small temperature readouts. Pics to follow...

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    Traced leads for the climate control buttons


    front:


    back (not reversed):



    I need a better way to get an image for the main board. It's so huge and it looks like I missed some areas in my pictures.

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    Maximum Bitrate Mickz's Avatar
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    Best of luck with this, a bit of info that may save you some time.

    As you know that button - Led interface board only holds some of the HVAC button and led’s that run with the Climate Control PCB. Tracing this and the main PCB will do you no good. The display encoder/decoder, data clock and control data comes from a Micro inside the Radio.

    Once the Radio is unplugged the LCD and all associated circuits are dead. No data clock signals, encoded data or radio- switch logic, no back light or LCD illumination control. The HVAC buttons and HVAC still function without the Radio-CD but of course there is no HVAC display.

    The LCD is a multi segmented device with a specialised driver the handles all the separate graphic segments, it also incorporates a key scan driver and data stream for all radio buttons. As this is dead without the radio and the micro inside of it there is no point in trying to hang something off of the LCD pins.

    I have already removed the Head unit from my Accord. The Car PC with 8” touch screen has full bidirectional control of the Climate control in the Accord. The Climate Control PCB has been relocated and interfaced with a custom Micro Controller that feeds data via USB back to the PC.

    There is a 2nd Micro that talks via a serial link to the HVAC Micro and gives full manual control if needed. This remote unit can also drive a small LCD. Both units can run standalone without a CAR PC.

    EDIT:

    Forgot to mention - There are NO connections between the HVAC CPU and the LCD display, even though they are on the same main PCB. The coded data from the HVAC CPU is sent to the radio where it is decoded and packetized for sending to the display driver via the Micro in the Radio.
    Last edited by Mickz; 02-25-2011 at 04:28 AM.
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    Thank you for the info. That's actually good news. Basically, I can isolate the climate controls but I won't be able to see the temperature I'm setting for it, is what I'm left with, correct?
    I'm not worried about which vents to activate or the window buttons, that's not info I needed (displayed visually on the LCD). The temp would have been nice but since Honda had to make it difficult, I'm not gonna cry over it.

    The main goal of this project is to shrink the main board and leave just the climate controls.


    -Ryven

    via iPhone

  5. #5
    Maximum Bitrate Mickz's Avatar
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    Correct, HVAC still works – but no temp display. On my dual climate control unit the driver temp control is around 16 positions, so it easy to set the temp blind if you had to. The LEDS for Auto, demist Rec etc still work.

    You may want a backup PCB before trying to cut or reduce the main PCB size. This is multi layer board and would be pretty hard to cut without losing control of the HVAC.

    If you just want a temp display on a small LCD then the decoder I designed can do that – but only for a dual climate unit, I have no idea if the data streams are the same for a single zone unit.

    There was enough lead length in mine (the two green plugs – leads going to the physical part of HVAC etc) to easily relocate the PCB into a small plastic case and move it to the back of the lower compartment, just in front of the ECU – TCU and SRS computers.

    Here is a thread I started on another forum – the Front End I’m writing has changed a lot from the early pictures in this thread. I have just finished redesignating the Micro controllers for the CAR-PC to Vehicle interface now that I have the IO and future expansion requirements design locked in.

    http://www.driveaccord.net/forums/sh...ad.php?t=52891
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    Mick, reading your thread on Driveaccord, all I can say is "wow".
    I remember seeing a post about you wanting to tackle this but it lead nowhere because it was before you actually started this thread and made such progress.

    I'm VERY interested in your DIY to isolate the climate controls to a dedicated LCD. I actually wanted them seperate from the PC so if I was just making a quick run down to the store in the winter, I won't have to turn my PC on to warm up the car.

    I've not chopped either board yet, but what I was hoping to do was redesign a board using only the needed components and after having a custom board made, desolder & reattach all the chips I need to keep from the old board. Like what this guy did but he has single zone and I thought I was starting from scratch to do dual-zone.

    Can you help me with a How-To? Of course, your stuff would be for no cutting of the board, while my intention is to completely redesign it to make it smaller. Aside from that, you've already accomplished exactly what I want to do!
    Last edited by Ryven; 02-27-2011 at 10:55 AM.

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    Maximum Bitrate nasa's Avatar
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    Holy !@#$,

    That is so sweet... I wonder if I would have to courage to do that! Nice work, Mick.

  8. #8
    Maximum Bitrate Mickz's Avatar
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    Hi Ryven.

    The single air-con control is not a climate control unit and is a simpler device to rebuild. The dual zone unit is a true climate control and takes input from inside/outside temperature sensors and a sunlight sensor. It is my personal opinion that your chances of tracing this circuit, dismantling the surface mount board and rebuilding a smaller unit are almost nonexistent. However it may be possible to remove the lower part of the board and LCD area.

    If I needed the room I would simply relocate the board to below the passenger seat.
    The two Green plugs/leads would be easy to run through the centre console and straight under the seat, the only control wire needed would be a 3 wire com cable to the small custom microprocessor Climate Control remote unit, no PC needed, possibly something worth thinking about.

    The micro interface to the Climate Ctrl PCB is very easy to make, it connects across the existing pushbuttons and LEDís. The Only mod to the board is the removal of the driver and passenger encoders as these are non standard mechanical encoders and can remain in an open or closed state.

    If you can get the common Microchip 18F458 40 pin Microcontrollers and have a means of programming them I would be happy to send you the program file for the HVAC interface and the Remote. You would have to realise that I would have make a few changes to the code Ė mainly the orientation of the LCD display as the driver and passenger positions are reversed to mine in AU. With that in mind it may take a few program mods and reprogramming at your end of the Micros to get it to display the way you want.

    I made it to operate without the PC right from the start as I donít want to be stranded in the middle of nowhere in our summer heat. BTW, the remote unit could be made into a wireless remote for climate control if you were inclined to do so.

    As a final note Ė Usually when you mod something like this it never turns out as easy to use and operate as the OEM unit. The Honda unit is one of the better laid out units that I have used.

    Everyone who has sat in the car has basically had a Jaw drop when viewing the running system. The touch screen implementation and the integration with the steering buttons (which are remapped on the fly for each application on screen) along with voice announcements, has not only made this a joy to use but the Climate control ease of use in now a big leap over the OEM setup.

    ---------- Post added at 11:12 AM ---------- Previous post was at 09:39 AM ----------

    Quote Originally Posted by nasa View Post
    Holy !@#$,

    That is so sweet... I wonder if I would have to courage to do that! Nice work, Mick.
    Hi, thanks for the words, the pictures of the front end donít do it justice. Itís designed around a 7Ē to 10Ē wide screen and the display in car looks very polished. I donít need or want player or menu navigation controls on any of the imbedded apps. The screens are switched with the steering wheel mode button or my current implementation of a simple iDrive.

    I wanted apps like GPS, DAB radio to have full screen display with no overlays. My criteria are safety first, no distractions when driving, one app at a time displayed full screen and instantly switched/selectable with steering buttons or iDrive. Along with voice announcements and no looking for a button on screen, this has resulted is a system that someone who has never driven the car can use in a matter of seconds.

    I take my hat off to everyone who has written a front end application, especially a generic front-end like the ones here on mp3. The amount of work involved is incredible

    Iím in the process of the final microprocessor programming and redesign of the system with inputs for a full ďiDriveĒ system. When itís all finished I may do another thread of the final build with circuits as Iím making the interface modules as non car specific as I can.

    Apology to Ryven if I have appeared to hijack his thread with my replies
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    No apology needed, Mick. My hat is off to you. Let me just rephrase for clarification:

    You would be willing to help me put together a small LCD display for my dual-zone climate control and instead of trying to reduce a very well-designed circuit board, I should box it up and relocate the beast similar to how you did, am I right? I've only removed the rotary knobs, the original LCD & I believe I've lost my 18-pin ribbon cable to connect the main board to the lower buttons, but I'm sure I can make a custom wire for that along with extensions for the green plugs and rotary dials.

  10. #10
    Maximum Bitrate Mickz's Avatar
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    All correct.

    I am in the process of rewriting the Microcode for the Remote. As soon as the revised circuit is complete I will post it here if you like. In the meantime I have finished the Climate Control interface redesign. I will post it as soon as I finish drawing the revised circuit. It really is a simple circuit. Apart from the I/O isolating diodes there are 3 resistors, 1 crystal, 1 transistor, 3 caps and the Micro.

    Mine is more complicated because the steering wheel control and general IO/ADC interface Microprocessor is mounted on the same board. These two micros share the same USB port back to the PC, so there’s a Data steering IC with associated logic that allows either Micro to access the PC and allows each to be updated with firmware with a touch of a button from the setup screen in my custom Frontend.

    The ribbon cable is not needed as you don’t need that small PCB. The hardest part of the conversion is soldering to the very small solder tabs on that socket that the ribbon cable went to. The easiest way to go would be to find a way to make a plug to fit the socket. I had no luck, but didn’t look around that much. I will do a close picture of the connections to the socket when I pull the system to fit the updated interface board. The other connections are simple as the LED’s and switches have big solder pads. All existing LED’s and switches can be left on the main board.

    Any questions or if you need anything clarified, please don’t hesitate to ask.

    Mike.


    Edit. You don’t have to extend the rotary dials. All controls and LED’s on the existing board are mimicked/available in the Remote unit via a serial com connection. However the remote changes the Temperature up/down to push button switches. If I get a chance I may reprogram the remote micro to use a couple of low cost rotary encoders.

    Mike.
    Last edited by Mickz; 02-27-2011 at 08:40 PM.
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    T-Screen HVAC control, custom microcontrollers, code and FE. CarPC Project

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