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.

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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 RMSMains 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 scopeThe 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-passA 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-passAn 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 responseTwo 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 resonanceA 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 filtersAn 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

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