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  • Current-to-Frequency Converter

  • Created: Jan 08, 2015

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Summary

Microchip's TC9402CPD IC is eminently suitable as an inexpensive current-to-frequency converter. The maximum input current of the design shown in the diagram is 10 µA (input voltage range is 10 mV to 10 V), while the output frequency range extends from 10 Hz to 10 kHz. The conversion factor is exactly 1 kHz/µA. The factor can be altered by changing the value of R1 - as long as the maximum input current of 10 µA is not exceeded.

The circuit has two outputs. That at pin 8 is a short-duration pulse, whose rate is directly proportional to the input current; that at pin 10 is a square wave of half the frequency of the pulse at pin 8.


Calibrating the circuit is fairly simple. Connect a frequency meter to pin 8 (preferably one that can read tenths of a hertz) and connect a voltage of exactly 10 mV to the input (check with an accurate millivoltmeter). Adjust R7 to obtain an output of exactly 10 Hz. Next, connect a signal of exactly 10 V to the input and check that the output signal has a frequency of 10 kHz. If this frequency cannot be attained, shunt C1 with a small trimmer or replace R1 by a resistor of 820 kΩ and a preset of 250 kΩ.

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