Relaxation Oscillator Using UJT, 555 Timer, Op-Amp

Relaxation Oscillator Using UJT, 555 Timer, Op-Amp

The relaxation oscillator is a transistor switch that generates saw-tooth and square waves. Saw-tooth waveforms have inconsistent voltage rise and fall directions. We know that the square waveform is the combination of saw-tooth waveform on and off stages since its voltage increase and fall are consistent. The relaxation oscillator is usually used to generate PWM.

You’ve probably heard of sound machines that play ocean waves or rainforest sounds to relax. Ever pondered what drives them? Relaxation oscillators create those soothing sounds. Here are several simple DIY relaxation oscillator circuits you can make with a few parts and no microcontrollers. I’ll demonstrate UJT transistor, 555 timer, and op-amp implementations. Soon, you’ll be relaxing to your own analog soundscapes with some simple electronics. These basic circuits will calm you whether you want to make a sound machine or play with electronics. Relax and let’s discuss relaxation oscillators!

Purpose of the Relaxation Oscillator

Relaxation oscillators create square, triangular, and pulse waveforms. A relaxation oscillator in electronic circuits is simple, cheap, and easy to customize for frequency and duty cycle. Transistors, 555 timers, comparators, opamps, digital timers, and others can implement the relaxation oscillator. This project uses UJT, 555 Timer, and Op-Amp to construct relaxing oscillator.

Overview of UJT, 555 Timer, and Op-Amp

Three components: UJT, 555 Timer, Op-Amp. UJTs are three-terminal devices with one PN junction. Triggering thyristors is its main usage in pulse generation and timing circuits. The 555 timer IC is utilized in timer, pulse generator, and oscillator applications. The 555 can delay time, oscillate, and flip-flop. Hans R. Camenzind’s 1970 555 timer is a popular timing and oscillator IC. Op-amps are basic electrical circuit components. As a differential amplifier, it has two inputs (− and +) and one output. Op-amps were created for general-purpose analog computers.

Importance of Relaxation Oscillator in Electronic Circuits

The relaxation oscillator is a popular electrical circuit. The capacitor charges and discharges through a resistor until its voltage reaches a specified point, then discharges till another point. This feedback mechanism in the relaxation oscillator helps create square waves and oscillations. Relaxation oscillator is a significant electronic circuit in many domains, hence a full study of its applications is crucial.

Relax! An Introduction to Relaxation Oscillators

Relaxation oscillators generate a continuous waveform without a sinusoidal input signal. Instead, they use capacitors and inductors to charge and discharge to oscillate. Circuit component values determine oscillation rate.
Buzzers, timers, and basic waveform generators use relaxation oscillators, which are easy to build. Unijunction transistor (UJT) and 555 timer relaxation oscillators are the most frequent.

The UJT Relaxation Oscillator

The UJT relaxation oscillator uses a unijunction transistor, resistors, and capacitor. UJT shifts states and discharges capacitor as it charges through one resistor. Capacitor recharges, repeating cycle. Timing resistors and capacitors determine oscillation frequency. Simple UJT oscillators lack stability and precision.

The 555 Timer Oscillator

Popular and multifunctional oscillator 555 timer IC. A capacitor and resistor coupled to the 555’s timing pins generate oscillations in its simplest configuration. The capacitor charges and discharges between the 555’s threshold and trigger levels, flipping between high and low output states. 555 oscillators are excellent for timing applications due to their frequency stability.

Op-Amp Relaxation Oscillators

Op-amps can be relaxation oscillators by connecting resistors and a capacitor in a feedback loop. The op-amp goes from saturated positive to saturated negative when the capacitor charges and discharges. Op-amp oscillators require more components but offer more design flexibility than UJT or 555 oscillators.

Without a sinusoidal input, relaxation oscillators generate oscillatory waveforms easily. Whether using discrete transistors, timer ICs, or op-amps, they simplify timing and waveform production.

Unijunction Transistor (UJT) Relaxation Oscillators

Universal junction transistor (UJT) relaxation oscillators are among the simplest oscillator circuits. UJTs’ unique features generate sawtooth waves.

The UJT has emitter, base 1, and base 2 leads. The UJT turns on when the voltage between the bases reaches a specified point, permitting current from the emitter to base 1. This rapidly discharges the circuit capacitor. Discharged UJTs turn off again, repeating the cycle. Charge and discharge of the capacitor produce sawtooth wave output.

A 2N4870 UJT, capacitor, two resistors, and power source are needed to make a basic relaxation oscillator. Connect base 1 to one capacitor end and ground to the other. Place a resistor between base 2 and ground. The other resistor should be between power and base 1. Connect the emitter to power last.

This simple circuit is versatile. Use it as a timer, pulse generator, or voltage-controlled oscillator. Timing capacitor and resistor values determine oscillation frequency. Any of these components can increase or decrease output frequency.

For enthusiasts and DIY electronics projects, UJT relaxation oscillators are easy to build with standard components. They output sawtooth waves from 1 Hz to 500 kHz or more. For beginners or those looking for an uncomplicated circuit to design, a UJT relaxation oscillator is a good choice.

555 Timer IC Relaxation Oscillators

555 timer ICs are common for timer, pulse generator, and oscillator applications. One of the simplest 555 timer oscillator circuits is the relaxation oscillator. This circuit generates a sawtooth waveform with few components.

A basic 555 relaxation oscillator requires the 555 timer IC, two resistors, and a capacitor. The capacitor charges and discharges to oscillate. Charge and discharge are controlled by the two resistors, which set the oscillation frequency.

The capacitor and power supply are connected by a charging resistor. Discharging resistor connects capacitor to ground. These two resistors govern capacitor charge and discharge, which determines oscillator frequency.

Connect pins 7 and 6 to operate the 555 timer in oscillator mode. The capacitor charges through the charging resistor and pin 2 goes high, setting the 555 timer flip-flop. Output pin 3 goes high. The capacitor discharges through the discharging resistor until the threshold pin detects a voltage decrease, resetting the flip-flop. Repetition creates a sawtooth wave at the output.

The two resistors and capacitor determine oscillation frequency. Calculate approximate frequency with this formula:

HZ = 1.44 / (Ω x μF)

Different resistor and capacitor values can be used to make 555 relaxation oscillators with frequency from 1 Hz to several hundred kHz. This simple circuit generates low-frequency clock signals, tones, and basic waveforms.

AMROs operate amplifier relaxation oscillators

Many analog circuits use adaptable integrated circuits called op-amps. Few-component op-amp relaxation oscillators produce continuous sinusoidal output. Building them is simple and helps you understand oscillators.

A simple op-amp relaxation oscillator requires an op-amp, two resistors, and a capacitor. Op-amps are comparators with positive feedback. The op-amp output controls the input through the capacitor and resistors, oscillating between the positive and negative power supply rails.

When power is applied, capacitor discharges. Positive rail receives op-amp output. Capacitors are charged by current through one resistor. The op-amp’s output immediately goes negative when the capacitor voltage hits its positive input voltage. Current discharges the capacitor through the other resistor. This cycle repeats, creating a square wave.

Adjusting resistor and capacitor values sets oscillation frequency. Lower resistances and capacitances produce greater frequencies, while higher ones produce lower frequencies. How long the capacitor charges and discharges determines its oscillation frequency.

Op-amp relaxation oscillators generate several frequencies. Simple, cheap, and easy to change by swapping parts. Function generators, clock circuits, and waveform generators use op-amp oscillators. They are wonderful oscillator and op-amp learning circuits. Grab some components and start tinkering—you’ll be relaxing with oscillators soon!

Metronomes to Neuron Modeling using Relaxation Oscillators

Relaxation oscillators are important in electronics and other industries. Though simple to build, they can create complicated output waveforms. Here are some major relaxation oscillator applications:

Relaxation oscillators are commonly used in metronomes. Mechanical relaxation oscillators make metronomes tick. The pendulum makes an audible “tick” at each extremity. Duration between ticks depends on pendulum length.

To simulate biological neurons and brain networks, neuromorphic engineering uses relaxation oscillators extensively. Capacitors can simulate neuron firing and signal buildup. These “spiking neurons” form neural route and brain function circuits.

Relaxation oscillators for clock signals, pulse-width modulation, and oscillating timers use 555 timer ICs. Changing resistor and capacitor values changes output waveform. Many commercial and amateur electronics use these simple oscillators.

Op-amp relaxation oscillators generate sine, square, and triangular waves for signal creation. These oscillators provide a variety of waveforms in function generators, analog synthesizers, and other circuits by modifying frequency and gain.

A basic oscillator circuit, relaxation oscillators have various applications. Relaxation oscillators will likely maintain electronics ticking, pulsating, or creating waves for years.


Relaxation oscillators are calm. One using a UJT transistor, 555 timer, or op-amp produces steady oscillations instead of sharp ones. Pretty laid-back. Relaxation doesn’t nap—it provides flexible duty cycles for switching power supplies, timers, alarms, metronomes, and more. Start your soldering iron and make one. The gentle oscillations will relax you without effort. Don’t forget your circuit is working when you’re having fun. Now, imagine sine waves slowing down for a leisurely afternoon nap. That’s soothing.

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