Digital Electronic Temperature Controller
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
A variable frequency oscillator is controlled by a thermistor. The oscillator's frequency is time-sampled by a counter. This count is then compared to a reference count which represents a command, setpoint temperature. Oscillator timing circuit 10 (a 555-type triggerable timer) includes a thermistor 11 as one of the oscillator's a stable-mode control resistors (Fig. 1). The oscillator's square-wave output pulses 12 vary in frequency by an amount which is proportional to the thermistor's temperature, an exemplary 72ŒF. A second, similar oscillator timing circuit 13 is controlled by 60 Hz line 14. Output 14 of this oscillator is divided by 60, using two counters 15 and 16. A flip-flop 17 provides a one-second gate pulse 18 to triggerable-timer 19 and NAND 20.