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I.What is a frequency to voltage converter?
Voltage Frequency Converter (VFC) is a device that implements an analog-to-digital conversion function to convert an analog voltage quantity into a pulse signal whose frequency is proportional to the magnitude of the input voltage.
Voltage Frequency Conversion can also be referred to as Volt-Frequency Conversion.Converting a voltage signal to a pulse signal significantly enhances the signal’s immunity to interference and facilitates long-distance transmission.
AD conversion can be realized by interfacing with the counter of the microcontroller.
II.Classification of frequency-voltage converters
There are two common types of VFCs:
(a) multi-harmonic oscillator VFCs; (b) charge-balanced VFCs.
Multi-harmonic oscillator VFCs are simple, inexpensive, low-power, and have a single-unit MS output (which is very convenient for connecting to certain transmission media); charge-balanced VFCs are more accurate than multi-harmonic oscillator VFCs, and are capable of integrating over negative input signals.
III.Circuit diagram of frequency voltage converter
After a capacitor is charged to a certain level, it discharges into a connected integrator or low-pass circuit, and this charging and discharging process occurs at all frequency cycles of the input signal.
A single multi-tuned oscillator and precision switches generate frequency pulses up to a specific amplitude and period, which enter the averaging network. Afterwards, the output of this filter is a DC voltage, completing the conversion.
IV.Frequency to Voltage Converter Circuit Diagram Using LM331
The LM331 is a high-precision frequency-to-voltage converter that can also be used as a voltage-to-frequency converter. It offers excellent linearity and wide dynamic range, ideal characteristics for a wide range of applications.
The circuit is very simple as you only need the following components:Six resistors, a trimmer potentiometer, three capacitors.
V.Frequency to Voltage Converter Circuit Diagram based on LM331 IC
The conversion begins by differentiating the input frequency using C3 and R7, and then feeding the pulse into the chip via pin 6. During the negative cycle of the frequency sine wave, the built-in comparator activates the timer circuit (R1 and C1).
At any given time, the current flowing out of the IC is always proportional to the input signal and the timer circuit value. Similarly, the output voltage will be proportional to the frequency signal of R4 (load resistor).
This is a circuit diagram of a very simple frequency to voltage (F to V) converter. This circuit has many applications in digital frequency meters, tachometers and other projects. The circuit is mainly based on the LM555 timer IC.
The IC is wired in mono mode and converts the input frequency to a fixed pulse width, variable frequency PWM signal. Resistor R4 and capacitor C2 provide the necessary timing for the circuit.
Transistor T1 forms a discharge path parallel to C2, which is necessary to retrigger the IC. Capacitor C1 is used as an input DC decoupler.
