Simple Adjustable Oscillator Circuit using Two Transistors

This article teaches how to use just two transistors to create a little sound generator circuit!

Turning a knob will change the sounds pitch from high, like a beep, to low like a growl.

Either four AA batteries or a tiny wall adaptor can power the circuit.

To explore how electronics may generate sound perform this easy experiment.

What is a Adjustable Oscillator Circuit:

A circuit that uses two transistors to produce an oscillating output signal is known as an adjustable oscillator circuit.

It uses two transistors that complement one another.

This circuits main aim is to generate an oscillation frequency that is steady and tunable.

Circuit Working:

Parts List:

The power supply voltage and the loudspeakers impedance define the oscillators current features which normally range from 10 to 300mA.

Pot P1 further increases the circuits adaptability by allowing the user to modify the operating frequency spectrum over a broad range of values.

It is possible to increase the lower control limit to around 10Hz by using potentiometers up to 1M to experiment with various frequency ranges.

The adjustment of capacitor C1 which allows for the testing of values between 0.01uF and 0.22uF impacts the circuits flexibility.

Higher C1 values will result in the production of frequencies in the lower spectrum of the range.

Because of this characteristic the circuit can get used for a variety of purposes including alarms, video games, toys and learning more about transistorized oscillators.

Formulas and Calculations:

By building a basic astable multivibrator circuit one can use two transistors to make an adjustable oscillator circuit.

A speaker can be powered by the continuous square wave output produced by this kind of circuit.

Here is how to make it with the essential formulas:

Compute Frequency:

For an astable multivibrator the oscillation frequency (f) is calculated as follows:

f = 1.44​ / (R1+2×R2) × C

where,

• R1 and R2 are the resistors connected to the base of the transistors.
• C is the capacitor.

Calculating Resistors and Capacitors Example:

Let say as per the diagram that R1 = 10k, R2 = 1k and C = 0.04µF.

Calculate the Frequency:

f = 1.44​ / (10kΩ+2×1kΩ) × 0.04µF

First convert the capacitor value to Farads:

0.04µF = 0.04×10⁻⁶F = 4×10⁻⁸F

Now substitute the values:

f = 1.44​ / (10,000Ω+2,000Ω)×4×10⁻⁸F

f = 1.44​ / 12,000Ω×4×10⁻⁸

f = 1.44​ / 48×10⁻⁵

f = 1.44​ / 0.00048 = 3,000 Hz

This results in a frequency of around 3kHz.

By adjusting the capacitor or potentiometer value one can modify this frequency.

How to Build:

To build a Simple Adjustable Oscillator Circuit using Two Transistors follow the below mentioned steps:

Collect Components:

• Assemble all required components including a small loudspeaker, transistors, resistors, capacitors and a potentiometer.

Power Supply Connection:

• The circuit is powered by four AA batteries or a constant 6 volt supply.

Adjust Frequency Spectrum:

• Use potentiometer P1 to generate the running frequency spectrum in order to identify the broad range of values for testing.

Experiment with Potentiometers:

• Experiment with potentiometers up to 1M to investigate a variety of frequency ranges and increase the lower control limit.

Modify Capacitor C1:

• To see how the capacitor C1 affects frequency generation experiment with values ranging from 0.01uF to 0.22uF.

Frequency Range:

• Check the loudspeakers audible frequencies which fall between 100 Hz and 2 kHz.

Application Testing:

• Examine how the circuits work in a variety of applications including toys, video games and alarms.

Conclusion:

By experimenting with various parameters one can adjust the performance of a basic adjustable oscillator circuit that uses two transistors for your needs.

To make sure a circuit is dependable and working always verify connections and parts twice.

References:

Electronic oscillator