VCO 0-200 Hz for boost gauge project

Discussion in 'The Projects Forum' started by MattStrike, Nov 2, 2011.

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  1. MattStrike

    Thread Starter New Member

    Jun 12, 2010
    14
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    I have a factory gauge cluster that has a boost gauge that doesn't fit the car, so I'm attempting to remove the gauge (which is a separate PCB from the main). The gauge reads from 0-10 psi normally. ('98 Pontiac Bonneville SSEi cluster)

    But, what I've managed to figure out thus far is that the slave board receives a Battery + voltage and ground from the main, and the gauge contoller IC receives a sine (or square?) wave from the the main. The wave frequency determines the reading of the gauge. If that wave circuit is open, the guage defaults to read 0 psi

    My first roadblock is that my wave generator only goes down to 200Hz. This is about 15psi on the gauge (max of 20 possible even though not marked on the guage). So I have to build a wave generator with a variable resistor and get me a oscilloscope to verify that I have the correct amplitude/voltage wave (or does voltage even matter on the wave generator output?..) I only have a DMM to test things with. I have found a few circuits that might work for the generator at this point, but nothing with specific info about the OP-AMP used? Can I use any OP-AMP to make a wave generator? I have a -15v..-1v,GND, 1v..15v power supply for testing (has the built in wave generator, both sine and square waves work on gauge, range 200 Hz - 20 kHz).

    Once I have the wave frequency that corresponds to the readings on the gauge face, I will need to make a VCO to interface with a MAP sensor, 0..5v i believe, I have a table of voltage vs. air pressure somewhere. But I'm not at that point yet. I can't find much technical info on the VCO circuit yet. Also, it will have to work on car voltage (12.8v - 14.1v), but OP-AMPs usually require a positive and negative reference to ground, not sure how to overcome that yet.

    Lastly, the shape of the slave pcb prohibits mounting it where I want, so I drew a schematic of the boost gauge pcb (also on this slave pcb are a voltage gauge and oil pressure gauge that appear to work in the same manner). Each of the sine wave inputs to the slave board go through a odd unmarked IC, referenced on the pcb as RZ1, before continuing to the controller for each respective gauge. This IC is smooth and white, 16pin with 1-8 on one side, 9-16 on the other. The only markings are (forgive my poor artwork, the .... are the white surface of the IC, the ||| the shape of the markings, --- is empty space, """ are the leads on the IC)

    ------------------------------
    ---..................................---
    """"..................................""""SIN input G1
    ---..................................---
    ---...||||||||||||||||||||...---
    ---...||||||||||||||||||||...---
    ---...||||||||||||||||||||...---
    """"...|||....................|||...""""
    ---...|||....................|||...---
    ---...|||....................|||...---
    ---..................................---
    """"..................................""""SIN input G2
    ---..................................---
    ---...||||||||||||||||||||...---
    """"...||||||||||||||||||||...""""
    ---...||||||||||||||||||||...---
    ---...||||||||||||||||||||...---
    """"...|||....................|||...""""
    ---...|||....................|||...---
    ---...|||....................|||...---
    ---..................................---
    """"..................................""""SIN input G3
    ---..................................---
    ---...||||||||||||||||||||...---
    """"...||||||||||||||||||||...""""
    ---...||||||||||||||||||||...---
    ---...||||||||||||||||||||...---
    """"...|||....................|||...""""
    ---...|||....................|||...---
    ---...|||....................|||...---
    -------------------------------

    Anybody recognize it?

    Any help is appreciated!
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    I am closing this thread as it violates AAC policy and/or safety issues.

    Quote:
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    Bertus
     
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