Simple Adjustable Oscillator Circuit using Two Transistors

This post shows you how to build a mini sound generator circuit with just two transistors!

You can adjust the sound to be high pitched like a beep or low pitched like a growl by turning a knob.

The circuit can be powered by either four AA batteries or a small wall adapter.

This is a simple experiment to learn how electronics can make sound.

What is a Adjustable Oscillator Circuit:

An adjustable oscillator circuit using two transistors is a type of electronic circuit that generates, an oscillating output signal and it employs two transistors working together in a complementary manner.

The purpose of this circuit is to produce a stable and adjustable oscillation frequency

Circuit Working:

Parts List:

The current characteristics of this oscillator are contingent upon the power supply voltage, the loudspeakers impedance and typically fall within the range of 10 to 300mA.

The circuits versatility is further enhanced by pot P1, which allows the user to adjust the running frequency spectrum across a wide range of values.

To experiment with different frequency ranges, potentiometers up to 1M can be employed extending the lower control limit to approximately 10Hz.

The flexibility of the circuit is also influenced by the modification of capacitor C1, where values ranging from 0.01uF to 0.22uF can be tested.

Increasing the values of C1 will result in the generation of frequencies in the lower spectrum of the range.

This feature makes the circuit adaptable for various applications such as alarms, video games, toys and for gaining additional insights into the world of transistorized oscillators.

Formulas and Calculations:

You will be building a basic astable multivibrator circuit in order to develop an adjustable oscillator circuit using two transistors.

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

Here is how to use the essential formulas and design it:

Compute Frequency:

For an astable multivibrator, the oscillation frequency (f) may be 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 us assume 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, you may modify this frequency.

How to Build:

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

Collect Components:

• Acquire the necessary components, including transistors, resistors, capacitors, potentiometer, and a small loudspeaker.

Power Supply Connection:

• Connect the circuit to either four AA cells or a constant 6 volt power supply.

Adjust Frequency Spectrum:

• Utilize potentiometer P1 to set the running frequency spectrum exploring the broad range of values for experimentation.

Experiment with Potentiometers:

• Experiment with potentiometers up to 1M to extend the lower control limit and explore diverse frequency ranges.

Modify Capacitor C1:

• Experiment with different values of capacitor C1 ranging from 0.01uF to 0.22uF to observe the impact on frequency generation.

Frequency Range:

• Observe the audible frequencies produced by the loudspeaker within the range of 100Hz to 2kHz.

Application Testing:

• Explore the circuits functionality in various applications such as alarms, video games, and toys.

Conclusion

You can build the two transistor adjustable oscillator circuit and experiment with different parameters to customize its performance according to your requirements.

Always double check connections and components to ensure a reliable and functional circuit.

References

Electronic oscillator