Introduction To First Order Filters

Understand, design, and simulate RC and RL, first order filter circuits.

What you'll learn

Understand the principles and behaviour of RC and RL filters

Calculate cutoff frequency, phase shift, and time constant for first-order filters

Build and test RC and RL filters on a breadboard

Use CircuitLab and TinkerCad Circuits to simulate filter circuits

Create Bode plots and phasor diagrams to analyse frequency response

Use Python to calculate and visualise filter behaviour

Apply filters in real-world applications like audio shaping and noise reduction

Design cascaded filter circuits to sharpen frequency response

Understand and apply key algebra and complex number concepts for filter analysis

Gain practical experience with measurement tools like the Analog Discovery 3

Requirements

A good understanding of basic electronics concepts, including Ohm’s Law, voltage division, and Kirchhoff’s Laws

Familiarity with AC circuits, reactance, and impedance

Basic algebra skills to rearrange equations, work with ratios, and calculate transfer functions

Some experience with complex numbers and phasors

A basic understanding of Python programming is helpful for following simulation scripts

If you’re new to electronics, I recommend taking my Introduction to Electronics course first

The course includes a primer on algebra and Python basics to help you refresh these skills as needed

Description

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 analysing and designing first-order RC and RL filter circuits.Hardware & SoftwareThis course uses a combination of simulation, data analysis, and circuit design tools to support your learning and experiments.PythonPython 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 dataSimulatorsThe 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.HardwareThe 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:ResistorsA range of resistor values will be useful for constructing RC and RL filters, typically:1 kΩ to 100 kΩ for standard filter configurationsAdjustable resistors (potentiometers) can be used for experiments requiring variable resistance.CapacitorCommon capacitor values include:100 nF to 10 µF for typical RC filter applicationsCeramic or electrolytic capacitors are both acceptable, depending on the experiment.InductorsFor RL filter activities, suitable inductors typically range from:1 mH to 100 mHValues depend on the desired cutoff frequency and practical considerations in your circuits.Breadboard and jumper wiresA 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.

Overview

Section 1: Introduction

Lecture 1 01.010 - Course overview and objectives

Lecture 2 01.020 - Software and hardware

Section 2: What is a filter?

Lecture 3 02.010 - Introduction to filters

Lecture 4 02.020 - First-order filters in real life applications

Lecture 5 02.030 - The four filters: low-pass, high-pass, band-pass, band-stop

Lecture 6 02.040 - Example: Compare a filtered and unfiltered signal

Section 3: Dive into first order RC and RL filters

Lecture 7 03.010 - Introduction

Lecture 8 03.020 - What is a first-order filter?

Lecture 9 03.030 - RC low-pass filter bevaviour

Lecture 10 03.040 - RC high-pass filter behavior

Lecture 11 03.050 - RL low-pass filter behavior

Lecture 12 03.060 - RL high-pass behavior

Lecture 13 03.070 - Voltage division in AC using reactance

Lecture 14 03.080 - Cutoff frequency

Lecture 15 03.090 - Phase shift

Lecture 16 03.100 - Step response of first-order filters

Lecture 17 03.110 - Impulse response of first-order filters

Lecture 18 03.120 - Just in case… definitions

Lecture 19 03.130a - Activity 1: Calculate filter response at low, cutoff and high frequenc

Lecture 20 03.130b - Activity 1: Calculate filter response at low, cutoff and high frequenc

Lecture 21 03.140a - Activity 2: Simulate sinusoidal input response in the time domain

Lecture 22 03.140b - Activity 2: Simulate sinusoidal input response in the time domain

Lecture 23 03.150 - Activity 3: Parameter variation study

Lecture 24 03.160a - Activity 4: Filter on a breadboard

Lecture 25 03.160b - Activity 4: Filter on a breadboard

Section 4: Filter analysis with Bode plots and phasors

Lecture 26 04.10 - Introduction to filter analysis with Bode plots and Phasors

Lecture 27 04.20 - What is a Bode plot?

Lecture 28 04.30 - Example Bode plots

Lecture 29 04.40 - What are phasors?

Lecture 30 04.50 - Example phasor plots

Lecture 31 4.060a - Activity 1: Calculate Missing Component to Achieve Desired Phasor Behav

Lecture 32 4.060b - Activity 1: Calculate Missing Component to Achieve Desired Phasor Behav

Lecture 33 4.070a - Activity 2: Design an RL high-pass filter for a target cutoff frequency

Lecture 34 4.070b - Activity 2: Design an RL high-pass filter for a target cutoff frequency

Lecture 35 4.070c - Activity 2: Design an RL high-pass filter for a target cutoff frequency

Lecture 36 4.070d - Activity 2: Design an RL high-pass filter for a target cutoff frequency

Lecture 37 4.080 - Activity 3: Bode and Phasor Plot from Measurement

Section 5: Filter applications

Lecture 38 05.10 - Introduction

Lecture 39 05.20 - Time constant and its meaning

Lecture 40 05.25 - Activity 1: Time constant experiment

Lecture 41 05.30 - Impact of time constant on signal shape

Lecture 42 05.35 - Activity 2: Impact of the Time Constant on Signal Shape

Lecture 43 05.40 - Audio tone shaping

Lecture 44 05.45 - Activity 3: Hear the effect of filtering

Lecture 45 05.50 - Sensor signal conditioning

Lecture 46 05.55 - Activity 4: A noisy light sensor with a filter

Lecture 47 05.60 - Noise filtering

Lecture 48 05.65 - Activity 5: Remove mains humming noise

Lecture 49 05.70 - Debouncing switches

Lecture 50 05.75 - Activity 6: Button debouncing on the breadboard

Lecture 51 05.80 - Analog smoothing of digital PWM signals

Lecture 52 05.85 - Activity 7: Smoothing of a PWM signal

Lecture 53 05.90 - Power supply filtering

Lecture 54 05.100 - Activity 8: Design a filter for a microphone

Lecture 55 05.110 - Activity 9: Design a filter for a thermistor or photoresistor

Section 6: Cascading Filters and Filter Types

Lecture 56 06.10 - Why cascade filters?

Lecture 57 06.20 - Cascading RC filters and second-order behavior

Lecture 58 06.25 - Activity 1: Cascading RC filters on the breadboard

Lecture 59 06.30 - Band-pass filter

Lecture 60 06.35 - Activity 2: Band-pass filter on the breadboard

Lecture 61 06.40 - Filter design constraints: loading, attenuation, bandwidth

Lecture 62 06.50 - Activity 3: Design a two-stage filter to isolate a frequency band

Lecture 63 06.60 - Activity 4: Simulate cascaded filters with varying cutoff frequencies

Section 7: A primer of plotting with Python

Lecture 64 7.10 - Why use Python to learn electronics?

Lecture 65 7.20 - Set up the Python environment

Lecture 66 7.30 - Python fundamentals for electronics simulations

Lecture 67 7.40 - Essential NumPy for electronics

Lecture 68 7.50 - Visualization with Matplotlib

Lecture 69 7.60 - Understanding and modifying electronics simulation scripts

Lecture 70 7.70 - Additional resources

Section 8: A primer of algebra for first-order filter analysis

Lecture 71 8.10 - Algebra in filter analysis

Lecture 72 8.20 - Rearranging equations

Lecture 73 8.30 - Ratios and proportions

Lecture 74 8.40 - Manipulating fractions

Lecture 75 8.50 - Powers and roots

Lecture 76 8.60 - Complex numbers

Lecture 77 8.70 - Frequency, angular frequency, and substitution

Section 9: Bonus

Lecture 78 Bonus lecture

Electronics enthusiasts who want to expand their understanding of filters,Hobbyists interested in practical electronics projects,Students looking to bridge theory and real-world filter applications,Learners who have completed my Introduction to Electronics course,Anyone with a good grasp of basic electronics and algebra wanting to deepen their knowledge in RC and RL filters