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Need help building a high temperature sensor

Discussion in 'Electronic Basics' started by Ray Manning, Aug 6, 2004.

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  1. Ray Manning

    Ray Manning Guest

    I'm looking for information on how to build a high temperature sensor for
    the HAI Omni Pro II home automation controler.

    Here's what I know:

    1) The HAI produced temperature sensors send frequency to the board and the
    board converts the frequency to temperature
    2) The formula for the conversion the board uses is T = F * 15 / 2 for
    3) the omni board does not handle temperatures over 120F, or 16 Hz

    What I would like to do is design a sensor which will monitor temperatures
    higher than 120F (low pressure boiler water). Since the board can't handle
    temperatures over 120F, I see two ways to accomplish this:

    1) send a Celsius temperature to the Omni instead of Fahrenheit. This would
    give me a high temperature of 120C or about 250F

    2) send an offset Fahrenheit temperature, for example (T = T - 100). This
    would basically drop the first digit which is quite acceptable in this
    situation especially since I use F everywhere else.

    Not knowing much about electronics, I'm not sure how to design this thing. I
    know I can us a LM34 to get the temperature but that outputs voltage (I only
    know that from google searches about temperature sensors for the SECU16). I
    don't know how to convert the voltage to frequency which matches the above
    formula. I also know the Omni sensors use thermistors based on 10k
    resistance and then calculate and convert the resistance to the appropriate
    frequency but that's no help to me since I don't know how that's done
    either. I know there are voltage to frequency converters but I have no idea
    how to hook one up to the LM34 to get the appropriate response.

    Any help or pointers on how to proceed?

    Ray Manning
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