BETALM331Voltage-to-frequency converter
Measure an analog voltage by counting its output pulses.
LM331 converts an analog voltage into a train of pulses whose frequency can be counted digitally. Its reference current source, comparator and timed switching circuit balance charge in an external integration network. Properly chosen components allow accurate conversion without a conventional parallel ADC interface. The example follows the manufacturer’s stand-alone voltage-to-frequency circuit with a15V analog supply and a5V output pull-up. A gain trimmer calibrates the nominal10V-to10kHz scale. The internal current output and the open-collector frequency output have different jobs and must be wired separately. This page covers TI LM331N/NOPB in its documented PDIP-8 package. No unverified SMD substitute is presented as the same TI device. Use stable resistors and low-absorption capacitors, calibrate the gain, and allow the input filter and integration network to settle before interpreting the pulse rate.
