Need a circuit that will trigger an alarm when a certain voltage is reached.

Discussion in 'The Projects Forum' started by damien89, Mar 21, 2009.

  1. damien89

    Thread Starter New Member

    Mar 18, 2009
    7
    0
    I need a circuit for my van which will trigger an alarm (beep of some sort) that i can connect with the factory temperature sensor. The circuit has to have an adjustable setting so that i can set it precisely a little bit above the normal running temperature.The existing sensor is a 'sender' type for an analog meter with thermometer pointer gauge scale.
    I have found this link which have this voltage switch:http://autospeed.com/cms/A_2476/article.html
    Would this work for my requirements?

    Thanks!
     
  2. bertus

    Administrator

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

    What are the working voltages of the temperature sensor at normal and high temparature ?
    You could make a comparator that compares the voltage of the sensor with a pre-adjusted value.
    The output of the comparator will give the "alarm" level.

    Greetings,
    Bertus
     
  3. skot9000

    Member

    Jan 28, 2009
    18
    0
    Damien89,

    from the linked website;

    "The Simple Voltage Switch (SVS) is a brilliant device because it allows you to trigger outcomes from any voltage outputting sensor on the car. That includes throttle position sensors, most airflow meters, most oxygen sensors, fuel level senders, temperature senders (both for the dashboard gauge and ECU), oil pressure senders and others."

    To me, it looks like this product will work quite well. It's probably overkill and overpriced for what you want to do, but then again your electronics experience level and amount of free time might make it worthwhile.
     
  4. damien89

    Thread Starter New Member

    Mar 18, 2009
    7
    0
    Hi,

    First of all thanks for the reply.
    Second, tomorrow i will check at what working voltages the temp. sensor operates.
    Then i will write the info here.

    Thanks again for your time!
    Damien
     
  5. damien89

    Thread Starter New Member

    Mar 18, 2009
    7
    0
    For now the only info i have is that the sensor works between 0-12volts and its resistance changes:

    • 60°C (140°F) = 146.6 Ohms (+26.5, -4.0)
    • 115°C (239°F) = 24.3 Ohms (+1.3, -1.8)
    Would this info be of any help? Because the plug that goes to the sensor is sealed and their is no way that i can stick a piece of wire in their to measure the voltage when cold and hot.:(
     
  6. bertus

    Administrator

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

    Where does the lead of the themosensor go ?
    You say it is linked to an analog meter with thermometer pointer gauge scale.
    Is there no way to get to the electric connection over there ?

    Greetings,
    Bertus
     
  7. damien89

    Thread Starter New Member

    Mar 18, 2009
    7
    0
    Actually it goes somewhere in the wiring harness but to get to the gauge i would have to take out the instrument panel. I will try to find a wiring diagram and see what i can do.

    Thanks
     
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