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Electrical track
Signals and filters

AC, signals and filters you can see on a scope

Sine, peak and RMS, reading a scope, RC low-pass, high-pass and band-pass, frequency response, RLC resonance and active filters.

FreeIn your browser2 courses, 14 lessons, about 8 hours
Start freeSine, peak and RMSSee the course
Overview

How you will learn it

Signals and filters are where electronics meets frequency: why a speaker crossover splits bass from treble, why a sensor reading needs smoothing and how a radio picks one station. The ideas are much clearer on a scope and a Bode plot than in an equation.

AC, signals and filters comes after Transistors and op-amps for real. Each lesson builds a filter, sweeps it and shows the result, ending with active filters built on op-amps.

Outcomes

What you will learn

  • Measure peak, peak-to-peak and RMS, and read a scope properly.
  • Design RC low-pass, high-pass and band-pass filters for a cutoff you choose.
  • Read a frequency response and find resonance in an RLC circuit.
  • Build active filters with an op-amp.
Your route

The courses and lessons to take

Every lesson opens in the editor right away, signed in or not, and the simulator checks each step.

  1. Step 1 · 7 lessons · 4 h

    AC, signals and filters

    The whole course.

    1. 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.
    2. 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.
    3. 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.
    4. 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.
    5. 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.
    Every lesson in the course
  2. Step 2 · 7 lessons · 4 h

    Transistors and op-amps for real

    The op-amp course this one builds on.

    Intermediate, after Electronics basics: the diode curve, biasing a BJT, common-emitter gain, the MOSFET as switch and resistor, op-amp gain both ways, comparators with hysteresis and split supplies.

    Every lesson in the course
Keep going

Guides and tools on the same subject

Track

Electrical track

Current and voltage you can see, then transistors, op-amps, filters, power and PCBs. Every circuit runs in a real circuit simulator in your browser.

See the whole track
Questions

Questions people ask

What is a cutoff frequency?

The frequency where a filter has let the signal fall to about 70 percent of its full size. For an RC filter it is 1 divided by 2 pi R C, and the lesson lets you check it on a sweep.

Do I need complex numbers?

Not to start. The lessons work from what the scope and the Bode plot show, and introduce the math only where it saves time.

Passive or active filter?

A passive RC filter is simple but loads the circuit and cannot add gain. An active filter uses an op-amp to fix both.