We can use any type of resistive transducer with central resistance in the range of 10 k ohms to 1 M ohms in the oscillator shown in the figure whose maximum output frequency is around 100 kHz. The output is rectangular with an active cycle that depends on the relationship between the resistance presented by the transducer and the resistance of 10 k ohms between pins 7 and 6/2. The sensors can be NTCs, PTCs, LDRs or others. The circuit can be used as an analog / digital converter (resistance / frequency) for remote sensing.
