NE566 - Voltage Controlled Oscillator (VCO)

There are other voltage-controlled oscillators like the 555. Some of the VCOs provide more than just square wave output.
For example, the NE566 function generator produces a very stable, easy-to-use triangle wave and square wave.
R1 and C1 elements set the center frequency in the NE566 circuit.
The control voltage is applied through voltage divider resistors (R2, R3, R4). The output frequency is found by the formula:

f =2(Vcc-Vin)/R1C1Vcc

NE566 Features:

A maximum of 12 Volt Vcc can be applied.
A maximum of 1 MHz can be generated.
R1 should be between 2k and 20K.
Vcc voltage should be a minimum of 0.75 volts.