VCO – Analog to Digital by 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. 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. 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.
Read more Source: Mr Anantha Narayan
http://schematics.blogspot.com/2005/01/vco-with-lm331.html
Thank you.
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