Source: https://mokxi.com/teachers/plans/signals-and-filters Updated: 2026-11-11 Lesson plan # AC, signals and filters lesson plan Advanced, after Transistors and op-amps for real: sine, peak and RMS, reading a scope, RC and RL filters, frequency response, RLC resonance and active filters. 3 chapters, 7 lessons, about 4 hours, no board. Every lesson runs in the browser, with nothing to install. Start a class from this course The unit ## Objectives and materials ### By the end, students can - What a sine really measures, and how to read one on a scope. - Low pass, high pass and band pass, and how to read a frequency response. - Resonance with an inductor and a capacitor, and filters with gain. ### Materials for the whole unit - Arduino Uno R3 - Capacitor x 2 - Diode x 2 - Frequency counter - Full-size breadboard - Function generator - Half breadboard - Inductor - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 2 - Op-amp - Oscilloscope - Piezo speaker - Potentiometer - Pushbutton - Resistor x 4 - Signal generator Every part is already on the simulator’s bench, so there is nothing to buy or hand out. The counts are the most any one lesson uses, if you build it on real breadboards too. Chapter 1. About 1 h 20 min ## AC signals What a sine really measures, and how to read one on a scope. Lesson | Time | What students do Sine, peak and RMS Mains through a 12-0-12 V transformer into a rectifier: what 230 V means when the peak is 325 V, why a 13 V winding charges a capacitor to 17 V, and what happens on the wrong mains. | 40 min - Mains, and a transformer - What RMS means - Find the peak - Why DC comes out higher than the label - The wrong mains - Peak, peak to peak, RMS Reading a scope The waveform lab: an Uno makes sine, triangle, sawtooth and square waves with PWM and an RC filter. Volts per division, time per division, period and frequency, checked with a frequency counter. | 40 min - Run it - Volts up the screen - Time across the screen - The slow end - Change the shape - Triggering ### Materials - Arduino Uno R3 - Capacitor - Diode x 2 - Frequency counter - Full-size breadboard - Half breadboard - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 2 - Oscilloscope - Piezo speaker - Potentiometer - Pushbutton - Resistor - Signal generator ### Check for understanding Each student finishes "Reading a scope" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Triggering". Chapter 2. About 1 h 40 min ## Filters Low pass, high pass and band pass, and how to read a frequency response. Lesson | Time | What students do RC low-pass A resistor and a capacitor with a meter on each side: full signal at 100 Hz, 0.707 at the 995 Hz corner, a tenth a decade above it, and the corner moved with one capacitor. | 40 min - Run it - The corner - Low frequencies pass - High frequencies are blocked - Move the corner up - The same filter in time High-pass and band-pass An inductor and a resistor with a meter across each: the inductor’s side passes highs, the resistor’s side passes lows, both read 1.0 V at the corner, and two filters in a row make a band. | 30 min - Run it - Highs across the inductor - Lows across the resistor - Slide the corner down - Two filters make a band Frequency response Two RC filters in a row with a meter after each: gain as a ratio and in decibels, the corner, and a slope that doubles to -40 dB per decade. How to read a Bode plot without needing one. | 30 min - Gain at one frequency - Gains multiply - A point below the corner - The slope - Reading the picture ### Materials - Capacitor x 2 - Full-size breadboard - Inductor - Multimeter x 2 - Oscilloscope - Resistor x 2 - Signal generator ### Check for understanding Each student finishes "Frequency response" on their own, without opening the hints. The simulator checks 5 of its 5 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Reading the picture". Chapter 3. About 1 h ## Tuned and active Resonance with an inductor and a capacitor, and filters with gain. Lesson | Time | What students do RLC resonance A resistor, an inductor and a capacitor tuned to about 1 kHz: the capacitor rings to four times the input at resonance, falls away either side, retunes with one part and sharpens as the resistance drops. | 30 min - Run it at resonance - Off resonance - Retune it - Sharpen it - Where resonance turns up Active filters An op-amp low pass on one 5 V rail: a gain of ten in the passband, a corner set by Rf and Cf, moved down a decade with one capacitor, and the trade between gain and corner. | 30 min - Gain and a filter at once - The corner - Above the corner - Gain against corner - Sharper filters, and the op-amp’s own limit ### Materials - Capacitor - Full-size breadboard - Function generator - Inductor - Multimeter x 2 - Op-amp - Oscilloscope - Resistor x 4 ### Check for understanding Each student finishes "Active filters" on their own, without opening the hints. The simulator checks 5 of its 5 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Sharper filters, and the op-amp’s own limit". Your class ## Teach this unit as a class Start a class from this course and its 7 lessons are assigned in one go, in order. Students join with a six-character code or printed login cards, and each one’s work comes back to you. The class tools are free for 30 days for one class of up to 20 students, with no card. The lessons themselves are free either way. Start a class from this course See the demo class More units ## Other lesson plans Electronics basics 20 lessons, about 10 h. Embedded on the Arduino Uno 16 lessons, about 12 h. Embedded on the ESP32-C3 13 lessons, about 11 h. Embedded on the Raspberry Pi Pico 7 lessons, about 6 h. Build your own fight stick 5 lessons, about 4 h. Embedded on the STM32F411 6 lessons, about 6 h. C++ on a board 13 lessons, about 10 h. Digital logic and memory 4 lessons, about 4 h. Interactive devices on the Uno 9 lessons, about 8 h. From gates to a computer 23 lessons, about 16 h. Build a claw machine 8 lessons, about 6 h. Every unit All the courses as ready-made units, on the teachers page.