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Thread: a questions about FB and its uses

  1. #1
    Newbie
    Join Date
    May 2004
    Location
    Vic, Australia
    Posts
    34

    a questions about FB and its uses

    ok so i've only JUST stumbled on this, i really should look more in the hardware discussion forum!!

    i was reading on the website to try and better understand what this can really do but i have a few basics questions:

    Firstly:
    i currently have 3 electronic gauges which have the electronic sensors to sense water temp, oil temp and oil pressure.

    can these electronic sensors be easily hooked up to the FB, so i could effectively have the computer display the information from these electronic sensors/senders?

    Secondly (and the most important one):
    i noticed a few threads about people talking about climate control, but it seems they have the old style buttons and slides, etc. my car actually has a digital climate control unit, pic below:



    now there are 9 buttons all up:
    1: A/C
    2: Fan Speed (4 speed settings)
    3: Vent Mode
    4: Temp Up
    5: Temp Down
    6: Off
    7: Auto
    8: Air Re-Circulation on/off
    9: Front Demister only.

    the wiring harness that connects to this unit, could i use that harness to effectively connect it to the FB and using the FB software have the carPC control the climate control?

    i hope i've been clear about what i'm asking. really interesting as i've been wanting to get rid of the digital climate control unit and have the carPC control it for awhile now.

  2. #2
    FLAC
    Join Date
    Oct 2006
    Location
    Las Vegas
    Posts
    1,286
    Those 3 sensors are very possible. It's one of the most fundamental functions of this board. One of the first steps for you to dig into this and find out how to implement it is to look at a few related things:
    Are these sensors currently being used as inputs to the vehicle's existing electronics (ECM)?
    If so, what range of voltage does the sensor operate?
    In addition to the brain and the sensors, you may only need a resistor or two to make it work. And worse case, maybe an opamp or two.

    As for climate control, the easiest way for you would be to interface the buttons on the control head. But there are some disadvantages to that method. One of the biggest ones is the need for a control system to have some feedback.

    If you tap into the harness, then you are going to be dealing with the components directly, and that usually means analog outputs would be needed.

    If it's not an automatic HVAC system currently, then you probably have:

    Either a blower resistor or, more likely, a mosfet based blower driver, so one of the wires will be an analog drive signal to the driver.

    Some of the wires in the harness will be for driving servos (all of the mechanical actators for your car are most likely servos, based on the way the interface looks) So those are either analog (0-5 or 0-12 or similar), or discrete value driven (which is less common, 0V close 2.5V hold 5V open, but easy to control). Other methods that may be used include PWM. Most of the servos (Mode, Temp, Recirc) will have a feedback potentiometer on the servo, which provides position feedback back to the control head.

    AC on/off, defogger, are usually just on/off signals to the BCM.

    If it is Auto, then there will be a few more sensors.

    So there is a lot of analog that needs to be controlled. And there are several methods where each is done. Just tapping in to your existing harness, while maybe possible, is going to take a lot of research. In addition, the currrent Brain offers no analog output capabilities, which requires some more components.

    One of the best ways to simplify things would be to research and utilize servos that will mechanically provide the same function (shaft size, rotation range, mounting points). I would prefer to drive a open-hold-close type with a feedback potentiometer. But one that drives open with one polarity and closed with another may work as well, as long as it holds it's position with no voltage applied. But really they're the same thing, just one has more circuitry involved.

    Once you find out how each servo is controlled, and the blower as well, and find out what inputs the head gets (interior temp, I assume, is one of them), you then need to find out some real specifics:
    There are several times where an AC compressor needs to be off, and the ECM usaully decides most of them, but sometimes the control head has one or more decisions to make before that AC request signal is passed along to the ECM.

    If you plan to replace the control head, you should provide, at minimum the same functions required originally of the head.

    For me that meant cracking it open. But in most cases, it requires thorough study of the vehicle service manual and HVAC schematics.

    But all in all its very possible, but it takes some work.

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