Linear temperature-to-frequency

  
This circuit provides a linear increase of frequency of 10 Hz/°C over 0-100 °C and can thus be used with logic systems, including microprocessors. Temperature probes Ql Vbe changes 2 mV/°C. This transistor is incorporated in a constant current source circuit. Thus, a current proportional to temperature will be available to charge Cl. The circuit is powered via the temperature stable reference voltage supplied by the 741
Linear temperature-to-frequency - schematic

Comparator ICl is used as a Schmitt trigger whose output is used to discharge Cl via Dl. To calibrate the circuit Ql is immersed in boiling distilled water and PR1 adjusted to give 1 kHz output. The prototype was found to be accurate to within 0 °C.




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