| AC |
Alternating current — flips direction (wall outlets) |
| amp (A) |
Unit of current; hobby circuits live in milliamps (mA) |
| anode |
The positive side (LED's long leg; diode's arrow side) |
| buck converter |
Efficient switching voltage regulator |
| capacitor |
Stores charge; smooths supplies, blocks DC |
| cathode |
The negative side (LED's short leg; diode's stripe) |
| cold joint |
Dull, cracked solder connection — reheat it |
| continuity |
Zero-resistance path — the multimeter's beep mode |
| current (I) |
Flow of charge, in amps |
| DC |
Direct current — one direction (batteries, USB) |
| decoupling capacitor |
0.1µF cap across a chip's power pins — prevents glitches |
| diode |
One-way valve for current |
| forward voltage |
The ~2V an LED drops while lit |
| GND |
Ground — the 0V reference |
| LED |
Light-Emitting Diode — polarized, needs a resistor |
| linear regulator |
Simple regulator that burns excess voltage as heat (7805) |
| multimeter |
Measures voltage, current, resistance, continuity |
| Ohm's law |
V = I × R — the one equation |
| open |
A broken connection (no continuity) |
| perfboard |
Pre-drilled board for soldered prototypes |
| polarity |
Which way round + and − go — getting it wrong breaks things |
| potentiometer |
Variable resistor — a knob |
| power (P) |
V × I, in watts — the heat budget |
| pull-up |
Resistor holding a pin at 5V when idle |
| resistance (R) |
Opposition to current, in ohms (Ω) |
| short |
Unintended zero-resistance path — the dangerous fault |
| solder bridge |
Accidental solder blob joining adjacent pads |
| strain relief |
Mechanical support so wire flex doesn't break joints |
| through-hole |
Components with leads through board holes (beginner-friendly) |
| tinned |
Coated with a thin solder layer (iron tips, wire ends) |
| voltage (V) |
Electrical "pressure," in volts |
| voltage divider |
Two resistors splitting a voltage proportionally |
| wetting |
Solder flowing smoothly onto metal — the look of a good joint |