# Need help building a high temperature sensor

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

1. ### Ray ManningGuest

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
conversion
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?

Thanks,
Ray Manning