Temperature To Pulse Width Converter Using LM3524

How to make a temperature to pulse width converter circuit. this is a simple circuit of temperature to pulse width converter.  The LM3524 to convert the output of an LM135 temperature transducer into a pulse width which can be measured by a digital system, such as a microprocessor controlled data acquisition system. In this circuit, the LM135’s temperature-dependent output (10 mV/°K) is divided down and applied to A1’s positive input.

Temperature To Pulse Width Converter Circuit Diagram:

Converter Circuit Diagram

This moves A1’s output high, driving the input to the LM3524’s pulse width modulation circuitry. The LM3524 pulse-width output is clipped by the LM185 reference and integrated by the 1 MW-0.1 µF combination. The DC level across the 0.1 µF capacitor is fed back to A1’s negative input. This feedback path forces the LM3524’s output pulse width to vary in a highly linear fashion according to the potential at A1’s positive input. Here is a schematic drawing:

The overall temperature to pulse width scale factor is adjusted with the “gain trim” potentiometer. The 1000 pF capacitor provides stable loop compensation. A1, an LM358, allows voltages very close to ground to be sensed. This provides greater input range than the LM3524’s input amplifier, which has a common mode range of 1.8–3.4V. The oscillator output pulse at pin 3 may be used to reset counters or other digital circuitry because it occurs just before the output pulse width begins.
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