What is an oscillator? Simply explained
Without oscillators, there would be no clocks, no microcontrollers, no radios, no sounds—in short: no modern electronics.
But what exactly is an oscillator? And why does almost every circuit need one?
In this article, I will explain to you simple and understandable, how oscillators work, what types there are, and where they are used everywhere – from Arduino to wristwatches.
What does an oscillator do?
An oscillator generates a periodic signal – usually in the form of a voltage that changes rhythmically:
e.g. a square wave signal (clock), sine wave (oscillation), triangle wave, etc.
You can think of it as a kind of electronic metronome:
beat, beat, beat – at exactly equal intervals.
Why is this important?
Electronic systems need a “sense of time” – e.g. to transfer data, synchronize processes, or define frequencies. No oscillator = no clocking.
Where is an oscillator used?
Microcontrollers (e.g., STM32, Arduino, ESP32)
→ require a clock signal in order to function. Internally, this is often an RC oscillator, externally, it is often a quartz crystal.
Wristwatches
→ Contain quartz oscillators with exactly 32,768 Hz → Ideal for obtaining 1 Hz = 1 second using a divider!
Radios / Radio transmitters
→ Use oscillators to generate and mix frequencies (e.g., 433 MHz, 2.4 GHz, etc.)
Audio (synthesizer, signal generator)
→ generate sounds through sinusoidal or other vibrations.
Power supplies (e.g., switching power supplies, boost converters)
→ regulate via oscillator frequencies, e.g. 100 kHz, 500 kHz, etc.
Side note for advanced users:
PLLs (phased locked loops) also contain oscillators – they synchronize clock signals and use them to generate higher or stable frequencies, e.g. for USB or SDRAM.
What types of oscillators are there?
1) RC oscillator
A resistor and a capacitor together determine the frequency.
Typically used in microcontrollers as an internal clock generator.
Simple, inexpensive, quickly available
Less accurate, temperature-dependent
Example: internal clock in STM32 with ±1–3% accuracy – good for PWM, poor for UART.
2) Quartz oscillator
A quartz crystal is set into vibration.
Highly accurate frequency – typically used in watches, radio systems, and microcontrollers.
Very stable and accurate (e.g., ±20 ppm = 0.002%)
Susceptible to mechanical stress, requires start-up time
Example: 16 MHz crystal on the Arduino Uno.
Or: 32,768 Hz quartz crystal in every quartz watch.
3) Oscillating circuit (LC oscillator)
A capacitor and a coil oscillate together.
Used, for example, in radios and RF technology.
Good for high frequencies
Frequency drifts due to temperature / component tolerance
Example: old FM receiver with rotary capacitor for changing frequencies → genuine analog radio feeling!
4) NE555 as an oscillator
The timer IC can be operated as an astable multivibrator, in which case it generates a square wave signal.
Universal, robust, easy to calculate
Not very accurate
Example: Flashing LED, buzzer, clock generator – the NE555 is a classic for hobbyists!
How does an oscillator work in principle?
Almost every oscillator is based on the principle of feedback:
Part of the output signal is fed back to the input—in exactly the right phase—and amplify itself.
If the circuit meets the conditions for a self-oscillation , it remains permanently active without an external signal.
→ That's called self-excited oscillator.
Side note for advanced users:
The Barkhausen criterion (gain = 1, phase shift = 0°) is the mathematical condition for stable oscillation.
Practical example: 555 oscillator for beginners
With an NE555 timer, two resistors, and a capacitor, you can build a square wave generator in two minutes.
Ideal as a clock for logic circuits, simple LEDs, or signal tests.
Formula for frequency:
f = 1.44 / ((R1 + 2 × R2) × C)
This allows you to generate a defined flashing frequency using simple components – perfect for initial testing.
Conclusion: Oscillators are everywhere
From the heartbeat of your microcontroller to the ticking of your wristwatch – oscillators are the sense of time in electronics.
They ensure regular processes, precise communication, stable frequencies – and can be found in almost every project.
Whether RC, quartz, NE555, or LC—each type has its advantages and disadvantages.
Once you understand this, you will be able to better plan, debug, and understand your circuits – and learn how clocking and timing really work.
FAQ – Frequently asked questions
What is an oscillator, explained simply?
An oscillator generates a periodic signal, e.g., a voltage that changes regularly—like a clock generator or electrical oscillating circuit.
Why do you need an oscillator?
For clocking in microcontrollers, signals in radio systems, time measurement in clocks, audio signals, or frequency control in power supplies.
What is the difference between a quartz and an RC oscillator?
A quartz oscillator is more accurate and stable, but usually external. RC oscillators are internal (e.g., in the MCU) and simpler, but less accurate.
How does an oscillator work?
It is based on feedback: part of the output signal is fed back and amplified, creating a continuous oscillation.