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VCO with LM331

This Circuit is a simple Analog to Digital Interface with a capability of 10 to 12 bits resolution. 10 bits means 1024 counts or parts of a full scale FS which is close to 3-1/2 1999 counts.

VCO with LM331

In this 1 V can be read as 1.000 V that means even 1mV can be resolved for FS of 1V. The Caps C6 and others must be plastic multilayer low-leakage types for accuracy of reading. Use all 1% MFR 100ppm or better resistors, Design gain of U1B for the Full Scale you want.

Mixed Circuits Analog with Digital

The Output Fout is a Frequency which is directly proportional to the measured voltage Vin. The pulses can be isolated using opto-couplers to avoid ground loops or electric hazard. An additional protection and scaling circuit at the input may be required for some sensors.

1 Hz or 1 PPS Crystal Clock Base

The CD4020BC, CD4060BC are 14-stage ripple carry binary counters, and the CD4040BC is a 12-stage ripple carry binary counter. The counters are advanced one count on the negative transition of each clock pulse. The counters are reset to the zero state by a logical “1” at the reset input independent of clock.

CD4040BC, 12-Stage Ripple Carry Binary Counters
CD4060BC, 14-Stage Ripple Carry Binary Counters

1 Hz or 1 PPS Crystal Clock Base

CD4060 – 14-Stage Ripple Carry Binary Counters

you can also use a crystal between pin 10 and 11 with two caps 22pF from 10, 11 to gnd and a 10M resistor between 10 and 11 in place of R C network for more precision.