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Thread: Old car/engine, non ODB, how to get RPM/speed/temp/etc into carputer

  1. #31
    Raw Wave Confused's Avatar
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    It worked the last time I drove the car
    Co-Developer of A.I.M.E.E
    www.aimee.cc

  2. #32
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    Here's the link to the picture of the digital dash that I'm working on. http://community.webshots.com/user/umsam
    I just got the layout made, but I only got the voltmeter to work so far. I just started working on it and I'll trying to make it universal so that it will work for any engine monitoring. Like I said in my earlier post, I'm using the "Easy Control" program and PIC microchip for data aquistion and sending the data to the computer via serial port. I might need some help in programming, if anyone can help. I also tried programming in VB, but this is much easier. I got simple VB programs to work with MScomm, but Easy Control is much nicer looking. I'll keep you guy posted when I get more time to work on this.
    66 Mustang

  3. #33
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    If you don't mind a new-guy pitching in...

    A few years back I built a digital display for my Mustang. At the time I only used a 40x4 character lcd display. I wanted to point out a few things about doing this project.

    1) not all sensors have a 2 wire connector, meaning they don't work as a voltage divider. Some, such as my oil and temp sensor were only one wire. To fix this I found other sensors utilizing the 2 wire, variable resister kind.

    2) most sensors for analog gauges are not linear. Meaning you'll have to use a look-up table to computer the actual values for given voltage. You may find these values on the net, but I simply took them to a physics lab, put them under measurable conditions, and measured the resistance.

    3) For most (at least mine) Fuel Injected engines, Central Fuel Injected included, have a square-wave generated by the distributor feeding into the ECU (engine control unit) this is perfect for tach readings, as i don't recomend reading off the coil.

    4) If you have cruise controll, you probably already have a readiably available source for your spedometer. Most cruse controll systems have either an adapter on the spedo cable gear in the tranny, or a hall-effect on the drive shaft (or whatever it's called on a front-wheel drive). If you don't have cruise control, as mentioned, Dakotah Digital makes a sensor that goes into your tranny, just like you original cable one, this will give off a pulse in ratio to your speed.

    5) I also don't recomend using a freq-voltage converter for these applications, mainly because of the resolution you require for an acurate reading. FVC utilize a charge pump to generate the voltage, depending on your ADC (analog-digital converter) you may not get the resolution you want. I do however recomend using the Timer/Counter registers on many of the PicMicro microcontrollers. This is an 8 to 16 bit register that increments on the rising edge of a pin attatched to that register (or falling edge if configured that way). When measuring freq, I simply cleared the counter register, called a delay for a certin amount of time then read the value, say I waited for 0.5s and the value in the register was 100, then the frequency is 200 times a second

    I have a simple schematic consisting of a zener diod, a cap, and a resister that will take a dirty ~12vdc input down to a clean 5vdc. I use this circuit on all inputs to my microcontrollers.

    BTW, the pic16f628, which sells for about $3.50, has 3 counters, 1 8bit and 2 16bit.

    I wish I had some pictures, but that was over 3 years since I had the car. I am about to do the same thing again, when I finish my home-made keyless entry, remote start, alarm system.

    If you have any question just ask. If I made a mistake please correct me but the information provided is to the best of my knowledge and is offered without any warrenty of any kind.

  4. #34
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    Oh, and for my new project I do plan on running the display from my SBC (single board computer) to increase the asthetics. I'm working with a home-built linux distro, I have my port access through a PCI card I built. The software for access is compiled into the kernel for very fast access. I've never worked with VB, so I can't offer any help there. But I do work in C/C++, java, and python, mostly for a linux system though.

  5. #35
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    Hey fastmoneywheel, Can you post or email me your "simple schematic consisting of a zener diod, a cap, and a resister that will take a dirty ~12vdc input down to a clean 5vdc." I'm doing the same with two resistors and a zener diode, but your design might be better. Oh, thanks for the info on the other stuff. I also use 16f628, it's so cheap and functional, includes 2 comparators and its own clock, only if it came with its own voltage regulator.
    66 Mustang

  6. #36
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    I got this schematic from a friend of mine who built his own programmable electric ignition for carburated 302's (ford). I'll try to draw it here

    input >-------/\/\/\/\---------------------------->output
    .............................................|.... ..........|
    ............................................---.........\__
    ............................................---............| \
    ..............................................|... ..........|
    ...........................................___.... .......___
    .............................................-...............-

    *note* dots are there because spaces disapear when this was posted**


    Ok, input goes though a .01K (10) ohm resister then a 1000pf crematic cap to ground, a 5.1v zener diod to ground, arrow or strip of diod towards input stream, then to microcontroller, or whatever.

    I also have a very good PSU unit for cleaning up the 12 volt supply that I use for my electronics...it's quite a bit more complex then this circuit. Leave me your email if you want it.

    It's clean enough to use an ISD400X series voice record/playback unit, which if you don't know needs a very clean powersupply.

  7. #37
    Constant Bitrate
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    Here is a diagram of this for those who could not understand the above example...

    Just a lil helper fastmonkeywheel
    Attached Images Attached Images  

  8. #38

  9. #39
    Raw Wave
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    fastmonkeywheel,

    Just a thought...

    The circuit you described is basically a voltage regulator and can sure work for PICs.

    I dont know how the 12V is provided but it may be floating when its supposed to be a zero volts. This leave the input of the PIC on a floating state and can cause unexpected results. I know theres a weak pull-up options on PICs but what is needed is a pull-down.

    If for example this 12V came from a relay, then its a case of a 12V or a float situations. Adding a pull-down resistor should easily fix this problems.

    Unless I already missed something

  10. #40
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    Ricky327, that's a good point. I use this circuit for switch input. Such as my doors or my trunk, whatever. I did use it for another input for something else, and it wasn't working right! I probably need a damn pull down resister...good call

    I'll search for that jpg and email it to you

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