Basic electromagnet
Wire round an iron core; current makes it magnetic, off and it isn't.
need enamelled wire · a nail or bolt · a battery
do wind a tight coil, scrape the ends, power it — picks up paperclips.
A coil of wire and a kick of current is half of every gadget you own. They pull, switch, clamp, strike, and sing — and they're hiding in every dead appliance. Here's the family, and what to make it do.
Wire round an iron core. Power on = magnetic; power off = nothing. The root of all the rest.
coil + coreA coil that yanks an iron plunger in when energized; a spring throws it back. Linear push/pull.
plungerA tiny solenoid that flips a switch — a small signal commands a big load.
switches powerThe flat coil in a speaker (and a drive's head arm) — fast, precise motion in a magnet's gap.
fast & preciseA solenoid that opens or shuts a fluid or air valve.
controls flowA sealed switch a passing magnet snaps shut — no contact, no wear.
magnet-trippedWire round an iron core; current makes it magnetic, off and it isn't.
need enamelled wire · a nail or bolt · a battery
do wind a tight coil, scrape the ends, power it — picks up paperclips.
Vary the current and you vary the pull.
need an electromagnet · a pot or PWM · a transistor
do PWM the coil — turn the field up and down on demand.
A switchable magnet grabs steel, then drops it on cue — the only magnet that lets go.
need a big electromagnet · an arm · a switch
do energize to grab, cut power to drop.
A relay's coil throws a switch — a tiny signal controls a lamp, pump, or motor it could never drive directly.
need a relay · a transistor + flyback diode · the load
do pulse the coil; its contacts carry the heavy current.
An electromagnet that interrupts its own power chatters a striker — the classic buzzer.
need a coil · a springy contact · a clapper
do run the coil through its own contact — it makes & breaks, and rings.
Relays were the first computers — wire them into gates and memory.
need a handful of relays
do cross-wire two relays to hold a state (a latch), or build an AND/OR.
Energize and the plunger slams in; a spring throws it back.
need a solenoid · a transistor + flyback diode · a supply
do pulse it — instant kick. Knockers, kickers, stampers.
A solenoid bolt you release electronically.
need a solenoid lock · a button or keypad · a driver
do press to pull the bolt; the spring re-latches it.
A solenoid opens or closes a fluid or air valve.
need a solenoid valve · a driver · tubing
do switch water or air on and off — irrigation, pneumatics, dosing.
Solenoids tap drums, bells, or keys on command.
need solenoids · strikers · a microcontroller
do fire each on the beat — a self-playing instrument.
A coil in a magnet's gap pushes a cone to move air.
need a magnet · a coil · a cone or membrane
do drive the coil with an audio signal — it plays.
Run it backwards: move the coil and it generates a signal.
need a small speaker · an amp input
do speak into it; the cone's motion becomes voltage.
A hard drive's arm is a fast, precise voice-coil mover behind a fierce magnet.
need a dead hard drive
do harvest the actuator for fast pointing — or just keep the magnets.
⚠ very strong magnetsA passing magnet snaps a sealed switch shut — no contact, no wear.
need a reed switch · a magnet
do door sensors, bike speedometers, hidden triggers.
A magnet sliding through a coil makes current (Faraday).
need a coil · a magnet · an LED (+ diode/cap)
do shake it — the LED flickers; store it to glow steady.
Two coils pass energy across a gap with nothing touching.
need two coils · an oscillator to drive one · an LED
do drive the primary at high frequency; the LED lights across the air.
A coil that pulls just enough, corrected by a sensor, floats a magnet in midair.
need a coil · a hall sensor · a control loop
do sense the magnet's height, trim the coil — it hovers.
An energized electromagnet clamps a steel plate hard; release by cutting power.
need an electromagnet · a steel strike plate
do door holders, fail-safe locks, work clamps.
workbench series · coils, cores, and a kick of current · mind the flyback and the heat