﻿ How to Build a Voltage-controlled Oscillator (VCO) Circuit with a 4046 Chip

# How to Build a Voltage-Controlled Oscillator (VCO) Circuit with a 4046 Chip

In this project, we will build a voltage-controlled oscillator (VCO) using a 4046 chip.

A voltage-controlled oscillator is an oscillator whose oscillation frequency is controlled by an input voltage.

Basically, the voltage input into the VCO chip controls how many times a digital signal will oscillate in a given time period.

The chip we will use is a 4046 chip. This is phase-locked loop IC. We will use the VCO portion of it to create our voltage-controlled oscillator circuit.

The voltage-controlled oscillator, as its output, produces digital signals that can function as clock signals. The output are digital values that oscillate repeatedly between 0 and 1, so that its value is 0-1-0-1-0-1...so on. This signal, in turn, can be input into a chip that needs a clock signal to function. This is one important and commonly used way of using a voltage-controlled oscillator (VCO).

### Components Needed

• 4046 Phase-locked loop IC
• 10MΩ resistor
• 220K1 resistor
• 1µF electrolytic capacitor
• 0.1µF film or disk capacitor
• 1N4001 power diode
• 1N4001 power diode
• 1N4733 5.1V zener diode
• Pushbutton (Normally Open)

The 4046 chip is a phase-locked loop. A phase locked loop IC consists of a voltage-controlled oscillator (VCO) and a phase detector. In this circuit, we will use only the VCO portion of the 4046 IC and not the phase detector. We use the chip just to generate a digital signal that can be used a clock signal.

The 4046 chip can be obtained very inexpensively (under \$0.50) and it's available from a number of different online retailers. One place to find is at Tayda Electronics at the following link: 4046 Phase Locked Loop IC.

The 4046 is a 16-pin chip.

The pinout for the 4046 is shown below.

Pins 1, 2, 10, 12, 13, 14, and 15 are not needed for to produce a voltage-controlled oscillator.

We will use a variety of resistors and capacitors to form RC networks that determine factors such as the rate of the voltage drain and the maximum oscillation. This you will all see in the circuit schematic below.

The zener diode acts as a voltage regulator, setting the voltage at 5.1V. across it, for voltage input into pin 4. This is the voltage that controls the number of oscillations for the output digital signal of the chip.

A pushbutton is used to activate the the 4046 chip.

The oscillator will produce a digital square waveform such as that shown below.