This circuit provides a linear increase of frequency of 10 Hz/Â°C over 0-100 Â°C and can thus be used with logic systems, including microprocessors. Temperature probes Ql Vbe changes 2 mV/Â°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
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 Â°C.