Practical Oscillator Circuits -- Article Index











Oscillators are the prime movers in practically all electronic circuits. Often an oscillator will be part of the circuit itself, generating a signal which is processed elsewhere to create the desired output. In other cases it might be remote, such as a distant radio transmitter, but even here most receivers incorporate oscillators of their own for use in signal processing. Indeed, it could be said that the oscillator is one of the most vital and frequently used types of circuit around.

To suit the huge variety of applications for oscillators there are many types of circuit for them. The aim of this guide is to present a wide range of these for enthusiasts to construct, experiment with and perhaps use in their own designs. The accent where possible is on the promotion of a thorough understanding of their operation. Basic circuits are covered, but where possible unusual techniques are also shown to encourage experimenters to develop novel designs of their own. All the circuits offered have been carefully "bench tested" to ensure that they will work correctly, and the advantages and limitations of each are explained clearly to enable the best choice to be made.

The oscillators are grouped into three main categories. The first covers circuits using resistors and capacitors to determine the output frequency, and these are further divided into four groups according to the type of active device used with them.

The first covers the ICM7555 and ICM7556 timer ICs. These versatile devices are ideal for oscillator design, used either by themselves or together with other devices such as op-amps. The next section covers designs employing various CMOS ICs, built from both individual gates and with special purpose designed ICs. This section ends with a circuit for the reliable generation of "white" and "pink" noise which has various uses, especially in sound effect creation, but is often difficult to produce. Op-amps can be used as oscillators so this is covered too, including a circuit for a practical high-quality audio signal generator. Finally the 8030 and the newer MAX038 "waveform generator" ICs are described, with details of their basic circuit configurations.

The next group covers circuits using inductance and capacitance for setting the output frequency. These are not so easy to adjust as the resistor and capacitor types but are much more stable, especially at higher frequencies. It is not always appreciated that they can be used at relatively low frequencies, or that some of the circuits using them can be very simple indeed.

For example, very stable signal sources may easily be built with small, inexpensive chokes and single CMOS gates, and if necessary a CMOS divider can reduce the frequency. Transistor and FET L-C circuits are also covered in detail.

Circuits using crystals to determine the output frequency are described next. These are extremely stable, and the increasing availability of both crystals and special ICs for driving them are making crystal oscillator design much easier than it once was.

Sometimes a single IC containing a built-in crystal and a programmable output divider can be used to generate an accurate reference frequency.

The final section describes practical construction techniques using "stripboard", using one of the circuits shown earlier as an example. This can be used to make a useful piece of audio test equipment which should find a place in many readers' work shops.

There is much pleasure and interest to be obtained from experiments with oscillator design. Hopefully this guide will encourage readers to venture into this area of the hobby for themselves by building and modifying the circuits shown, and then perhaps producing new designs of their own.

Practical Oscillator Circuits

One of the most frequently used electronic "building blocks" is the oscillator, and the aim of this guide is to provide a rich source of these for enthusiasts to experiment with and perhaps use in their own designs.

Extensive coverage is given to circuits using capacitors and resistors to control frequency. Designs using CMOS, timer ICs and op-amps are all described in detail, with a special section on "waveform generator" ICs. Reliable "white" and "pink" noise generator circuits are also included.

Various circuits using inductors and capacitors are covered, with emphasis on stable low frequency generation. Some of these are amazingly simple, but are still very useful signal sources.

Crystal oscillators have their own section. Many of the circuits shown use readily available special ICs for simplicity and reliability, and offer several output frequencies.

Finally, complete constructional details are given for an audio sinewave generator, which will prove to be a most useful piece of test instrument for any enthusiast's workshop.


Please Note:

Although every care has been taken with the production of this guide to ensure that any projects, designs, modifications and/or programs, etc., contained herewith, operate in a correct and safe manner and also that any components specified are normally available; but, we do not accept responsibility in any way for the failure, including fault in design, of any project, design, modification or program to work correctly or to cause damage to any other equipment that it may be connected to or used in conjunction with, or in respect of any other damage or injury that may be so caused, nor do we accept responsibility in any way for the failure to obtain specified components.

Notice is also given that if equipment that is still under warranty is modified in any way or used or connected with home-built equipment then that warranty may be void.

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