Frequency Hz to Voltage Calculator

This tool calculates the output voltage from a tachometer from the input frequency.


Enter the values of

  • Frequency (use the drop down menu to select the units)
  • Supply Voltage (VCC)
  • Resistor
  • Capacitor




VOUT = fIN * VCC * R1 * C1

The output voltage is equal to the product of the input frequency, supply voltage, resistance and capacitance.

Example Calculation

For input frequency of 1 kHz, VCC = 15 V, R1 = 100 kΩ and C1 = 0.01 µF the output voltage is equal to 15 mV.


A tachometer is a device used to measure the rotational speed of a shaft or disk in machinery. Tachometers often convert the frequency of the rotational signal into a voltage signal for display or further processing.

The picture below shows a tachometer that uses LM2907 and LM2917 voltage to frequency converters from TI

The process typically involves a few key components and steps:

  1. Signal Pickup: The tachometer first picks up the rotational signal from the machinery. This is usually done using a sensor or transducer that generates electrical pulses as the shaft or disk rotates. Common types of sensors include magnetic pickups, optical sensors, or Hall-effect sensors.
  2. Frequency-to-Voltage Conversion Circuit: The electrical pulses generated by the sensor represent the frequency of the rotation. To convert this frequency to a voltage signal, a frequency-to-voltage converter circuit is employed. This circuit typically includes components such as a voltage-controlled oscillator (VCO), a counter, and a filter.
    • The VCO generates a voltage signal with a frequency proportional to the input pulses.
    • The counter may be used to measure the frequency by counting the number of pulses over a specific time period.
    • The filter helps smooth out the signal and eliminate noise.
  3. Output Voltage: The output of the frequency-to-voltage converter is a voltage signal that is directly proportional to the rotational speed. As the rotational speed increases, the frequency of the input pulses increases, leading to a higher output voltage. Conversely, a decrease in speed results in a lower output voltage.
  4. Display or Further Processing: The converted voltage signal can then be displayed on a meter or fed into other systems for additional processing or control purposes.

It’s important to note that the specific design of a tachometer can vary, and different models may use different techniques for frequency-to-voltage conversion. The key principle remains the same: converting the rotational frequency into a proportional voltage signal for measurement and display.

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