NE566 Function generator | Voltage Controlled Oscillator VCO circuit

We have many ways to make the function generator. Using NE566/LM566 is a good choice. Because it easy to use. It looks like a NE555 timer.

And we often use the NE566 as Voltage controlled oscillator or VCO circuit. It is a type of oscillator. We can control the frequency of the output with the amplitude of an input voltage signal.

LM566 Function generator _ Voltage Controlled Oscillator VCO circuit


  • Wide range of operating voltage (up to 24V; single or dual)
  • High linearity of modulation
  • Highly stable center frequency (200ppm/°C typical)
  • Highly linear triangle wave output
  • Frequency programming by means of a resistor or capacitor, voltage or current
  • Frequency adjustable over the 10-to-1 range with the same capacitor


Here are examples using them on a lot of applications.

  • Function generators
  • Tone generators
  • Frequency shift keying
  • FM modulators
  • Clock generators
  • Signal generators

NE566 pinout

It has the same shape as NE555 on DIP8. But the legs are used differently. Let’s see the NE566 pinout below.

NE566 pinout

Block diagram

What is VCO? Look at below.

VCO Block Diagram
VCO Block Diagram

It is a VCO (voltage-controlled oscillator) of linearity with buffered square wave and triangle wave outputs.

Look at the block diagram inside NE566 IC.

NE566 Block Diagram
NE566 Block Diagram

We can control the frequency of oscillation by an external
resistor(R1) and capacitor(C1) and the voltage applied(VC) to the control terminal.

NE566 Equivalent Schematic
NE566 Equivalent Schematic

The oscillator can be programmed over a ten-to-one frequency
range by proper selection of external resistance and modulated
over a ten-to-one range by the control voltage, with exceptional

You probably want to use it. And of course, the circuit examples are always a wonderful assistant to our good understanding.

Function Generator circuit

This is a simple Function generator circuit on two waveforms. The important part of the circuit is LM566 or NE566. It produces Sawtooth(Triangle) and Square waves from 1Hz up to 1MHz. The amplitude of the voltage offset and duty cycle is adjustable to offer a wide range of generated signals.

Triangle and Square wave generator using NE566

We use VR1 to adjust a control voltage (VC) to control the output frequency oscillator. We can find the center frequency (F)

F = 2 (Vcc – VC)/ (R1 C1 Vcc)

The power supply voltage is 9V to 24V.


NE566 or LM566 is a general-purpose voltage controlled oscillator that highly stable, easy to use.

It produces Triangle and Square waves. R1 and C1 control the center frequency and the voltage at pin 5.


  • The level of output will not drop to 0V.
  • If 12V power supply (pin 8) the triangle waveform will be 4V to 6V and the square wave will be between 6 volts to 11.5 volts.

Check out these related circuits, too:

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I always try to make Electronics Learning Easy.

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