How To Build A Simple Transistor Oscillator

Transistor oscillator Image source Quora

You are working on an electric project and you need it to generate oscillations. What is the first component? that will come into your mind? For most of us, we will think of a timer. But is it the only solution? Are there alternative ways of generating and managing electronic oscillations? Yes, you can use other components. Transistors are among the alternative electronic components that are used for making oscillators.  The simplicity of transistors is they allow you to build a fully functional oscillator. In this article, we are going to discuss how to build a simple transistor oscillator.

What is a transistor oscillator?

In the world of electronics, oscillation refers to the behavior of the electronic signals to make repetitive motion within a central point. These signals can be power signals, audio signals, or any other type of signal that is designed to perform a specific function in an application. The oscillations have all the key characteristics of a typical waveform. They have amplitude and frequency.

Oscillations are generated by oscillators. They are designed to generate oscillations that have defined frequencies and waveforms. Most electronic applications depend on oscillators for controlling the behavior of the signals. Take an example of the radio-frequency signals. Other than being generated, they need to be accurately timed. This is where the relevance of the oscillators comes in.

By utilizing the working principle of positive feedback, an oscillator takes part of the output signal back into the input stream whereby it will be used for making the input signals. By doing so, it is able to sustain the oscillations for a long period.

There are different types of oscillators and most of them are named based on the electronic components that have been used for making them. RC oscillators are made of resistors and capacitors while LC oscillators are made of inductors and capacitors. Others are named based on their working mechanism. For example, Voltage-controlled oscillators are named so because they depend on power to control the frequency of oscillations.

For the transistor oscillators, depend on transistors not only to generate but also to control the behavior of the oscillation frequency. Other than amplification and switching functionalities, transistors are also known for being used as oscillators.

Transistor oscillators are not only used in simple electronic applications but also, they are widely used in many commercial applications. Most radio transmitters and receivers depend on the power of transistors to generate and control oscillations.

Using transistors in oscillators

In a typical transistor oscillator, the oscillations generated by a transistor are not affected by the incoming signals. Instead, the direct input current from the power source into the circuit is converted into AC signals.

In an oscillator circuit design, a transistor is positioned to serve as an emitter of the circuit. The circuit is connected to the base and the emitter terminals. This circuit also has a capacitor and the inductor which are connected parallel to the signal generator. The signals at the base terminal keep changing mainly due to the constant fluctuation of voltage at the generator.

Building a simple relaxation oscillator using transistors

You can build a simple oscillator using a BJY transistor. The BJT transistor will be able to execute the oscillations when operating on the negative avalanche mode which is capable of generating fast rise pulses. This mode is affected when the connections on both the collector and the emitter are reversed. This ends up creating a negative avalanche region on the circuit which will eventually lead to the generation of the pulses. Also, in the negative avalanche mode, you will only use two terminals of the transistor and not three as in other modes.

What do you need to build this oscillator?

You will need a transistor, an LED, and a capacitor. For the power source, you will need about 10-18 volts for the oscillator to function. You can easily get these from simple battery cells. A current-limiting resistor may also be needed to regulate the flow of current to the LED. This resistor also regulates the charging process of the capacitor. A potentiometer may also be needed for the oscillator to run smoothly.

Since this is a simple DIY project, you will use a stripboard to host the circuit. It is strong and can easily support al the active electronic components. The board will also allow you to solder items on it without causing any damage.

Design the oscillator layout

Now that you have all the parts in place, the next step of the process is to draw a circuit layout of the transistor oscillator. The simplest way is to arrange all the components in the strop board and then mark the input and output sections on the board.

During the design phase, try to visualize the locations and positions of the components on the board. This will ensure that all of them fit perfectly.

Drilling and soldering

After designing, you can start doing the actual work on the stripboard. But before doing so, determine the sizes of the holes for the components and conductors. With each hole that you drill, mark the exact component that you will insert. A drill bit will come in handy whenever you want to do these drills.

This step will require protective glasses. Once you are done, test all the components to verify that they fit in the holes before proceeding to the next step.

Solder the circuit

Since the circuit board is ready, you can lay out all the components on the holes that you had drilled on the previous step. This step will require that you refer to the schematic diagram of an oscillator as illustrated below

Image source Instructables

Once all the components are in place, you can proceed to solder them on the stripboard. Remember to cut off all the excess wires and conductors.

Put everything together

At this point, we assume that you have soldered all the components on the board (transistors, capacitors and potentiometers) on their respective holes that you drilled on the board. The next step is to verify that everything is well-secured. You can use a perf board lid to secure the circuit.

A duct tape and screws may be used to secure the lid in place as shown in the image below.

Image source Instructables.com

Rectify all the mess and you will have your functional transistor oscillator ready to use.

Check out the video below for a detailed tutorial.

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