# Mission: Inductance for microcontroller & DC electronics

## Why

Charlie builds microcontroller projects that switch motors, solenoids and relays,
and currently copies those circuits from other people's schematics without owning
the reasoning. Inductive loads are where copied schematics stop being enough — the
part that kills MCUs, welds transistors and causes unexplained resets. The goal is
to move from *copying* inductive-load circuits to *designing* them.

**Live project (as of 2026-08-07):** driving a 6 V (max) brushed DC motor from a
generic ESP32 dev board, one direction, on/off — no PWM, no reverse. Two circuits
exist side by side as teaching examples: one with the motor **straight off a GPIO
pin**, one with the motor switched by a **transistor** driven from a GPIO pin.
The trigger for learning was realising a flyback diode was needed without knowing
why. Lessons should use this exact circuit wherever possible.

## Success looks like

- Given a relay/solenoid/motor datasheet, calculate coil current, stored energy, and
  the size of the turn-off transient — before building anything.
- Choose and size a clamp (plain diode / diode+resistor / zener / TVS / RC snubber)
  from the actual trade-off, not from a schematic found online.
- Pick a switching device (BJT / MOSFET / driver IC) with ratings justified against
  the load, including the turn-off transient.
- Explain to someone else why a given circuit's protection components are there.
- Diagnose an inductive-load failure (dead MOSFET, MCU reset, chattering relay) from
  symptoms rather than by swapping parts.
- **Near-term:** state confidently why the direct-to-GPIO motor circuit is wrong,
  and defend every component in the transistor version from its ratings.

## Constraints

- **Bench:** multimeter, bench PSU, function generator, breadboards, soldering iron.
  **No oscilloscope** — transients cannot be observed directly, so lessons must supply
  simulation or use indirect, DMM-and-eyeball-friendly experiments.
- Starting point: comfortable wiring circuits from schematics; not yet deriving why
  each component is present. Assume no calculus fluency; build the intuition first,
  then the equation.
- Learning is self-paced across multiple sessions.

## Out of scope (for now)

- AC mains, transformers, and magnetics design (winding your own inductors).
- Switch-mode power supply design — buck/boost converters are a natural sequel, but
  chasing them now would split focus away from load driving.
- RF, antennas, and transmission-line effects.
- PCB layout and EMC compliance testing.