Inductance for MCU & DC
Relays, solenoids and motors are where copied schematics stop being enough. This is the workspace for learning to design those circuits instead — one bench, one motor, no oscilloscope.
New here? Start with Lesson 01. The lessons build in order; the reference sheets are the printable residue of each one, and are worth keeping beside the bench.
Every lesson here is anchored to one real circuit: a 6 V brushed DC motor driven from a generic ESP32 dev board, one direction, on and off. Two versions of it sit side by side as teaching examples — one with the motor hanging straight off a GPIO pin, one with the motor switched by a transistor. Working out precisely why the first is wrong, and defending every component in the second, is the near-term goal.
The bench has a multimeter, a bench supply and a function generator, but no oscilloscope. Transients cannot be watched directly, so the lessons supply a simulated instrument where the real one is missing, and otherwise stick to experiments a DMM and a pair of eyes can actually settle.
Lessons
The sequence
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01
The current flywheel
Why opening a switch is more dangerous than closing one — and why the coil, not you, decides what voltage appears next.
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02
What a pin can and cannot do
Two motor circuits on the bench, one straight off a GPIO and one through a transistor. How to tell which is right before powering either one up.
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03
Choosing the transistor
Sizing a switch from your measured stall current, and the 3.3 V gate-drive trap that catches most ESP32 projects.
Reference sheets
For the bench, not the sofa
Each sheet is the compressed output of its lesson — equations, datasheet numbers and the trade-off, on one page that prints properly. Read the lesson once; keep the sheet.
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R01
Driving an inductive load
The equations, the G5V-2 relay numbers, and the one trade-off that every clamp choice sits on.
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R02
The pin budget
Three gates every load must pass before it can hang off a microcontroller pin — and the one component that fixes each.
Scope
What this covers, and what it doesn’t
In scope
Load driving from a microcontroller: coil current and stored energy, sizing the turn-off transient, choosing a clamp, choosing a switching device, and diagnosing a failure from symptoms rather than by swapping parts.
Out of scope, for now
AC mains and transformers, winding your own magnetics, switch-mode supply design, RF and transmission lines, and PCB layout or EMC compliance. Buck/boost is the natural sequel — chasing it now would split focus away from driving loads.