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Custom car mod

Discussion in 'General Electronics Discussion' started by DeathhGhost, Aug 11, 2015.

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  1. DeathhGhost


    Aug 11, 2015
    I understand the basics and a little more.
    I am asking for your opinions on how to do this project.

    I want to use the wire for my cars speedometer and display the speed on a small screen using java or something to program from a laptop.

    I got the idea from a gps stereo with the ability to display maps, speed, rpms. Now I want to make a custom one that I can modify.
    Car : 07 WRX

    Thank you
    Last edited: Aug 11, 2015
  2. martin the warrior

    martin the warrior

    Aug 10, 2015
    I'm no expert on how to program. But I can tell you how the signals are sent in the car. the wheel speed sensor is a DC analog signal, that signal goes to an ABS module then the speed information is sent to the instrumental panel/cluster module that will then control the gauges. basically using the wires straight form the gauge wont work unless the processor can understand voltage. the signal that is sent between modules is a binary number like 1100101101 or what ever. I'm not sure how helpful this is. let me know how it works out. by the way i'm an automotive/diesel technician and can answer any questions you might have if this was not helpful. you can also buy after market parts that will do this.
  3. Gryd3


    Jun 25, 2014
    You can also look into these displays. Some can be programmed directly ;)

    As far as interfacing is concerned, you can either tap into the data lines directly... which could cause some major issues* or you can use the OBD port and pull the data from the ECU.
    The OBD method will not respond as quickly as tapping into the sensor wires, but if you tap into a sensor wire incorrectly and accidentally alter a signal, your car can do some pretty odd and potentially dangerous things. I'm not too familiar with the make and model, so I'm unsure what kind of 'active' computer controlled features you have.

    Martin as absolutely correct here though too... many of the data lines can be one of the following.
    - Analogue Voltage 0 - 12V.
    - Analogue Voltage 0 - 3 or 5V.
    - "Digital" logic.. ie, 12V or 0V for things like door switches
    - Digital communications using binary 1s and 0s to send information. (These lines can be one direction or bi-directional)
    - PWM
    - Frequency

    There is truly a very wide range of signals to read. Digital communication may be the hardest to read, as the communication protocol may not be documented in a resource that you have access to, the rest are pretty easy. At least with OBD access, the on board computer will deal with these sensors for you. You just have to eaves-drop, or ask it for specific values to show whatever you want. This will also prevent you from making a rats'nest of wiring that would scare everybody away from every possibly buying the car when you are done with it, or fixing it if it breaks.
  4. martin the warrior

    martin the warrior

    Aug 10, 2015
    since Gryd3 added the voltage specs for the sensors. i will add that sensors have a + .5v from the 0 and -.5v from the top; for example if the operating range of the sensor is 0-5v it is actually .5-4.5v this helps the OBD to do diagnostics if the sensor reads lower than .5v there is resistance somewhere in that circuit if it reads zero there is an open in the circuit and if it reads higher than 4.5v there is a short to power. just keep that in mind if you do go right off the sensor but i agree with Gryd3 probably not a good idea. and now that i think about it grabbing the binary information would be hard since lots of different information is sent over the CAN. i would also agree that requesting the speed information form the power control module or engine control module would be best.
    Gryd3 likes this.
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