Introduction to electronics - Filters

Understand, design, and simulate

RC and RL, first order filter circuits.

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This course introduces the foundational concepts of RC and RL filters, empowering you to understand, design, and analyze these essential circuits. You will explore how these filters control and shape electrical signals through low-pass and high-pass configurations, and learn how to determine critical parameters such as cutoff frequency and phase shift. The course also covers real-world applications of these filters, from audio tone shaping and noise removal to sensor signal conditioning and switch debouncing.

The course structure combines short, focused video lectures, clear explanations, and practical activities that build your knowledge progressively. Throughout, you will engage in simulation-based exercises and breadboard experiments, applying your understanding to real-life situations. Key activities include calculating filter responses at various frequencies, visualizing behavior with Bode plots and phasors, and examining how cascading filters can improve performance.

To support your learning, you will use Python, CircuitLab, and the Analog Discovery 3 for simulations and practical measurements. If you do not have this hardware, you can still follow along with the demonstrations and Python exercises, using online simulators or your own measurement tools. Downloadable resources and exercises ensure you can apply what you learn immediately, gaining practical skills in designing and analysing RC and RL filters.

Who is this course for?

This course is designed for electronics enthusiasts, hobbyists, and students who already have a solid foundation in basic electronics concepts, such as Ohm’s Law, voltage division, and working with simple circuits. If you have completed my Introduction to Electronics course or have equivalent experience, you are well-prepared to dive into RC and RL filters and expand your understanding of how these essential building blocks shape and control electrical signals.

Whether you’re looking to reinforce your skills with practical, hands-on experiments or you want to explore real-world applications like audio shaping, sensor conditioning, and noise filtering, this course will guide you step by step. It is an ideal next step for learners who want to bridge the gap between theory and practice, and build confidence in analyzing and designing first-order RC and RL filter circuits.

Learning objectives

By the end of this course, you will be able to:

  • Explain the role and characteristics of RC and RL filters in electronic circuits
  • Identify and calculate cutoff frequency, phase shift, and time constants for first-order filters
  • Simulate and analyse RC and RL filters using CircuitLab, Python, and hardware tools.
  • Understand and apply Bode plots and phasors to visualise filter performance.
  • Design and build simple filter circuits to improve audio signals, sensor readings, and power supply noise.
  • Explore practical applications, such as tone shaping, noise reduction, signal smoothing, and sensor conditioning.
  • Cascade first-order filters to achieve sharper frequency band isolation and second-order behaviour.
  • Use Python to perform simulations, automate calculations, and visualise data for filter analysis.
  • Reinforce your knowledge of essential algebra and complex numbers used in filter design.

Throughout the course, you will gain practical experience through simulations, breadboard experiments, and measurement exercises, ensuring a well-rounded understanding of RC and RL filters in real-world contexts.

Knowledge prerequisites

To get the most out of this course, you should have a good working knowledge of basic electronics principles. Specifically, you should be comfortable with:

  • Ohm’s Law and basic circuit analysis
    Understanding the relationship between voltage, current, and resistance is crucial for calculating component values and analysing filter circuits.
  • Voltage division and Kirchhoff’s Laws.
    These fundamental rules are applied throughout the course when determining how signals are distributed across components and understanding the behaviour of RC and RL filters.
  • Basic algebra and manipulating fractions.
    You will need to rearrange equations, work with ratios and proportions, and apply powers and roots when calculating transfer functions and filter responses.
  • Basic Python programming.
    Some familiarity with Python is helpful for following and modifying simulation scripts in the course. You’ll use Python for calculations and to visualise filter responses.

If you’re new to electronics, I strongly recommend taking my Introduction to Electronics course first to build this essential foundation.

If you feel you need a refresher on the mathematics or Python programming skills required, the course includes dedicated primers at the end to help you get up to speed.

These resources ensure that you have the confidence and knowledge needed to tackle RC and RL filters effectively.

Hardware & Software

Software

This course uses a combination of simulation, data analysis, and circuit design tools to support your learning and experiments.

Python

Python is used throughout the course for data analysis, visualisation, and calculation of filter responses. If you do not have Python installed, you can download it from the official Python website. The course includes a primer on essential Python skills, and uses the following libraries:

  • NumPy for numerical calculations and managing arrays.
  • Matplotlib for creating plots and visualising data

Simulators

The course demonstrates filter behaviour using online circuit simulators that make it easy to build and analyse circuits:
  • CircuitLab is an intuitive online simulator that allows you to create and analyse circuits, measure filter responses, and experiment with circuit designs.
  • Tinkercad Circuits is another accessible, web-based tool that lets you build and simulate circuits interactively. It’s ideal for beginners and can be used for exploring basic RC and RL filter behaviour.

WaveForms (for Analog Discovery 3 users)

If you have the Analog Discovery 3 device, you can use the WaveForms software to generate signals, measure filter responses, and capture data. This powerful tool integrates an oscilloscope, waveform generator, spectrum analyser, and other instruments, making it ideal for hands-on experimentation.

The course includes detailed instructions and resources to help you set up and use these software tools, even if you are new to them. If you prefer to work with other simulation tools, you can still follow the principles and adapt the examples to your preferred environment.

Hardware

The practical activities in this course are designed to be accessible and flexible, using commonly available electronic components. Aside from a mini-breadboard, you will need the following:

Resistors

A range of resistor values will be useful for constructing RC and RL filters, typically:

  • 1 kΩ to 100 kΩ for standard filter configurations
  • Adjustable resistors (potentiometers) can be used for experiments requiring variable resistance.

Capacitor

Common capacitor values include:

  • 100 nF to 10 µF for typical RC filter applications
  • Ceramic or electrolytic capacitors are both acceptable, depending on the experiment.

Inductors

For RL filter activities, suitable inductors typically range from:

  • 1 mH to 100 mH
  • Values depend on the desired cutoff frequency and practical considerations in your circuits.

Breadboard and jumper wires

A breadboard and jumper wires will allow you to build and test your circuits without soldering.

Oscilloscope (optional)

An oscilloscope helps to visualise filter responses in the time domain, but if you do not have one, you can follow along with the demonstrations and simulations in the course.

Signal generator (optional)

A standalone signal generator can be a useful tool for testing filter performance with different input waveforms. If you do not have a signal generator, the Analog Discovery 3 or your computer’s audio output (for audio-range signals) can serve as alternatives.

Analog Discovery 3 (optional)

The Analog Discovery 3 is a powerful, all-in-one instrument that can function as a signal generator, oscilloscope, and spectrum analyser. It’s highly recommended for deeper experiments in filter response and real-world circuit behaviour.

If you do not have access to the optional hardware, you can still complete all simulation-based activities and follow along with demonstrations for the hands-on experiments. The course is designed to be accessible and practical, regardless of the hardware you have on hand.

This course does not include any hardware! Please source your own hardware from your preferred retailer. 

More information about this course

Overview & objectives

Software & Hardware

Introduction to filters

Sample lectures

Filtered vs unfiltered signal

Filter on a breadboard

PWM smoothie

Here's what you're getting:

  • "Introduction to Electronics - Filters" video course.
  • Over 70 video lectures in 4K.
  • Each lecture is supported by video and notes.
  • Learning is enhanced with practical bench experiments, simulations, and detailed walkthrough experiments on screen.
  • Dedicated community discussion space (with Community Tier purchase).
  • Lifetime access.

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What's in this course?

1 - Introduction
Course Overview and Objectives
Review of software and hardware tools used

2 - What is a filter?
Introduction to filters
First-order filters in real life applications
The four filters: low-pass, high-pass, band-pass, band-stop
Example: Compare a filtered and unfiltered signal

3 - Dive into first order RC and RL filters
Introduction
What is a first-order filter?
RC low-pass filter bevaviour
RC high-pass filter behavior
RL low-pass filter behavior
RL high-pass behavior
Voltage division in AC using reactance
Cutoff frequency
Phase shift
Step response of first-order filters
Impulse response of first-order filters
Just in case... definitions
Activity 1: Calculate filter response at low, cutoff and high frequencies
Activity 2: Simulate sinusoidal input response in the time domain
Activity 3: Parameter variation study
Activity 4: Filter on a breadboard

4 - Filter analysis with Bode plots and phasors
Introduction to filter analysis with Bode plots and Phasors
What is a Bode plot?
Example Bode plots
What are phasors?
Example phasor plots
Activity 1: Calculate Missing Component to Achieve Desired Phasor Behavior
Activity 2: Design an RL high-pass filter for a target cutoff frequency and sketch the Bode and phasor plots
Activity 3: Bode and Phasor Plot from Measurement

5 - Filter applications
Introduction
Time constant and its meaning
Activity 1: Time constant experiment
Impact of time constant on signal shape
Activity 2: Impact of the Time Constant on Signal Shape
Audio tone shaping
Activity 3: Hear the effect of filtering
Sensor signal conditioning
Activity 4: A noisy light sensor with a filter
Noise filtering
Activity 5: Remove mains humming noise
Debouncing switches
Activity 6: Button debouncing on the breadboard
Analog smoothing of digital PWM signals
Activity 7: Smoothing of a PWM signal
Power supply filtering
Activity 8: Design a filter for a microphone
Activity 9: Design a filter for a thermistor or photoresistor

6 - Cascading Filters and Filter Types
Why cascade filters?
Cascading RC filters and second-order behavior
Activity 1: Cadcading RC filters on the breadboard
Band-pass filter
Activity 2: Band-pass filter on the breadboard
Filter design constraints: loading, attenuation, bandwidth
Activity 3: Design a two-stage filter to isolate a frequency band
Activity 4: Simulate cascaded filters with varying cutoff frequencies

7 - A primer on Python for filter analysis
Why use Python to learn electronics?
Set up the Python environment
Python fundamentals for electronics simulations
Essential NumPy for electronics
Visualization with Matplotlib
Understanding and modifying electronics simulation scripts
Additional resources

8 - A primer of algebra for first-order filter analysis
Algebra in filter analysis
Rearranging equations
Ratios and proportions
Manipulating fractions
Powers and roots
Complex numbers
Frequency, angular frequency, and substitution

The course instructor

The course instructor is Peter Dalmaris, PhD.

Peter has created over 20 other courses on technology education.

He is the author of Maker Education Revolution, a book on how making is changing the way we learn and teach.

He is also the host of Stemiverse, a podcast in which he discusses education and STEM with the shakers and movers of technology and science education from around the world.

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