Temperature transmission

I suggest you make a voltage to frequency converter, to change the temperature signal to an audio tone. Use that to modulate the FM transmission. At the receiving end, you change the frequency of the tone back to voltage, or measure the frequency, digitally, and convert to temperature with a look up table. There are lots of ways to do voltage to frequency, from a 555 and LM2907. But there are also temperature sensors that output frequency, directly. See page 6 of:

Or you could convert the temperature signal to a variable duty cycle digital signal (variable mark/space ratio), and modulate the FM with one of two tones for the two variable times per cycle. You would have to convert the received pair of tones back to the two digital values (see LM567

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Another one on page 10:

hi, i like to tell something abt the same project, that is temperature indicator using 89c51.ie,v r doing digital thermometer,it consist of a sensor,LM35 which is acting as a current to voltage converter, n the output of the sensor will b given to an ADC whose output is in digital format.This digital format information is our temperature whcih is in the form of voltage.Inorder 2 convert it to corresponding temp,v uses a microcontroller,ie 89c51.And the output of the mc wil provide to the LCD display.

And if it is needed v can provide additional facilities like temp range indicator etc.acually i wan ur help inorder 2 modify the same project with additional ideas ie using this same principle other than temp measurement can v do somethin else with the same circuit.ie extra fittings.thank u

On a sunny day (19 Feb 2007 05:04:14 -0800) it happened "SR" wrote in :

Max and min temperature, logging to a file for the year, humidity with a different sensor, air pressure with an other sensor, wind speed and direction with yet an other sensor..., radioctivity with [], light sensor for the shades, and count the sunny days, rain sensor, sound pressure sensor, lightning detector, CO detector, other gasses detector, passive IR detector, etc... Enough?

Location, location and location. We would like to log the absolute location of an unstable hillside. With heavy rains for the past few days here, I wish we have it in place already.

Why not measure temperature using an MG or a Citroen?

John P.'s suggestion of using analog telemetry is good if all you're ever going to do is measure one thing. If there's any hint that you'll want to measure other quantities consider using some low rate digital telemetry. I'd suggest 300 baud FSK, or perhaps 1200. This should be easy to implement, it should work just dandy with the serial output of your microprocessor, and you'll be able to send just about anything you can dream up.