Digital Speedo and Odometer circuit

Discussion in 'The Projects Forum' started by Bear_2759, Dec 22, 2008.

  1. Bear_2759

    Thread Starter Active Member

    May 23, 2008
    120
    0
    Hi All,

    I need some assistance, what I am doing is creating a whole new dash for my car, so far I have (all analogue) Tacho, Speedo, Temp and Fuel. thanks to SgtWookie for allot of help with most of these.

    I would like to have alongside this, a Digital Speedo and Odometer, partly because I am required by law to have an odometer in the car if I want it to pass rego.:p.

    what I want, 2x LCD Display's, 1 that is min 3char long to display speed. another that is min 6 char long to display odometer reading. odometer must have a memory that is not cleared if the main battery to the car is disconected. I'm constantly playing with my car so it get's disconected every couple of weeks...

    I've done a bit of "googling" and all the circuit's I've found seem to be somewhat outdated or just use a 3 segment LED display not a LCD display.

    any help is much appreciated.
     
  2. Bear_2759

    Thread Starter Active Member

    May 23, 2008
    120
    0
    ok so after a bit more searching, I did find this, http://www.edn.com/article/ca529384.html

    it all looks pretty good to me, I did find a few places where people had success with this one. there's only 1 thing. on the page describing the circuit it says that the odometer will work from 0-9999.9km. however in the source code it says 0-99999.9... this is the first time I will have played with a PIC so don't really understand much when it comes to this form of code... what I need to know is where the typo is, is it in the code, or in the article. for me, a odometer that only goes up to 9999 won't be much use, but 99999 is perfect...

    also if anyone has any suggestions for updates to this circuit because I think it's a few years old.

    thanks in advance.
     
  3. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    You will need a microcontroller for sure.. And the above circuit I guess uses its own wheel spin detector.. Thats not a smart idea..
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    I looked at the source code and can tell you this:

    The designer have used three 8-bit registers to accumulate the total distant travelled. The first register is incremented every now and then.

    If the first register's value exceed 99, then it is cleared to zero and the next register is incremented by 1. If this second register exceeds 99, then the last register is incremented by 1.

    Using these three registers, the value that can be stored in this way is at least 999999. If the first register increments by one every 0.1Km distant travelled, then the total Km that can be stored is 99999.9Km.

    Hope this answer your question.
     
  5. Bear_2759

    Thread Starter Active Member

    May 23, 2008
    120
    0
    perfect, that's exactly what I needed to know. and the circuit will suit perfectly as this is what the original odometer went to in the car... thanks for letting me know.

    Yep, I figured that the way they had the hall efect sensor setup was not very good ;), so I plan on removing the old speedo cable from the gearbox and putting a hall efect sensor in it's place. this will be much more acurate and how speed is measured in most modern cars. then all I need to do is mod the maths in the code to suit, at the moment my guess is I would need to know gear ratio's, dif ratio, and wheel size... but I can work that out later with a bit of trial and error :p. thanks.
     
  6. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Ohh if you're planning to remove your current setup, then this is the best way.. You dont need to have compatibility problems of their specifications matching yours. You can make them just the way you need.. Run the best cable you can to your gearbox, find the revs for 1 unit and make that value standard for 1 unit in your source code.
     
  7. Bear_2759

    Thread Starter Active Member

    May 23, 2008
    120
    0
    sorry I don't quite follow? what I plan on doing is using the circuit in the first post, replacing the speedo cable with a Hall-effect sensor at the gear box. this will output a frequency as the gear teeth pass the sensor. there would no longer be a cable from gearbox to speedo. then I just need to work out how many times the frequency hits the peak (can't remember the terminology at the mo. it's been a long day) for every 100m and mod the source code to suit.
     
  8. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    thats it.. as I meant
     
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