Reference chart
Electronics glossary
Print it: Circuit symbols cheat sheet (PDF: A4 · US Letter)
Electronics has a lot of words. This glossary explains each one in a sentence or two, in plain English, with a link to the guide that teaches it properly.
A
| Term | What it means |
|---|---|
| AC (alternating current) | Current that keeps reversing direction, usually as a sine wave, like the mains. More |
| ADC (analog-to-digital converter) | A circuit that turns a voltage into a number. An Arduino Uno's gives 0 to 1023 across 0–5 V. More |
| Aliasing | A fast signal sampled too slowly looks like a slower, false one, like wagon wheels turning backwards on film. More |
| ALU (arithmetic logic unit) | The part of a CPU that adds, subtracts and does logic on numbers. More |
| AM (amplitude modulation) | Sending a voice by making a radio carrier's height rise and fall with it. More |
| Amp (ampere, A) | The unit of current: one coulomb of charge passing each second. More |
| Amplifier | A circuit that makes a signal bigger. Its gain says how many times bigger. More |
analogRead() | The Arduino function that reads a voltage on pins A0 to A5 as a number from 0 to 1023. More |
| AND gate | A logic gate whose output is 1 only when every input is 1. More |
| Anode | A diode's positive end, where conventional current goes in. More |
| Antenna | A conductor that turns a signal into radio waves, or radio waves back into a signal. More |
| Arduino | A family of microcontroller boards you program in C++, through setup() and loop(). More |
B
| Term | What it means |
|---|---|
| Band-pass filter | A filter that passes a band of frequencies and cuts those above and below it. More |
| Bandwidth | The range of frequencies a circuit passes, often measured between its −3 dB points. More |
| Base | The control terminal of a bipolar transistor. A small current into it lets a bigger one flow. More |
| Battery | One or more cells that store chemical energy and deliver it as a voltage. More |
| Binary | Counting with only two digits, 0 and 1, where each place is worth double the one to its right. More |
| Bit | One binary digit, a 0 or a 1. More |
| BJT (bipolar junction transistor) | A transistor, NPN or PNP, where a base current controls a larger collector current. More |
| Bode plot | A graph of gain in decibels against frequency on a log scale. More |
| Boolean algebra | The maths of true and false, with AND, OR and NOT, used to simplify logic circuits. More |
| Boost converter | A switching circuit that steps a DC voltage up. More |
| Breadboard | A board of spring clips in rows, for building circuits without soldering. |
| Bridge rectifier | Four diodes that turn both halves of an AC wave into DC. More |
| Buck converter | A switching circuit that steps a DC voltage down with little waste. More |
| Byte | Eight bits, enough to count from 0 to 255. More |
C
| Term | What it means |
|---|---|
| Capacitor | Two plates with a gap that store charge and energy. It blocks steady DC and passes changes. More |
| Carrier | The steady high-frequency wave that a radio signal rides on. More |
| Cathode | A diode's negative end, marked with a band, where conventional current comes out. More |
| Charge | The property of electrons and protons that makes electricity, measured in coulombs. More |
| Circuit | A closed loop that charge can flow round, from a source through a load and back. More |
| Clock | A steady square wave that tells a digital circuit when to take its next step. More |
| Closed loop | Control that measures the result and corrects for the error. More |
| Collector | The bipolar transistor terminal that the load current flows into, on an NPN. More |
| Combinational logic | Logic whose outputs depend only on its inputs right now, with no memory. More |
| Comparator | A circuit that compares two voltages and swings its output to say which is higher. More |
| Complementary filter | A way to blend a gyro and an accelerometer into one steady angle. More |
| Conductor | A material, like copper, that lets charge flow easily. More |
| Conventional current | Current drawn as flowing from + to −. Electrons actually drift the other way. More |
| Coulomb (C) | The unit of charge, about 6.24 × 10¹⁸ electrons. More |
| Counter | Flip-flops wired to count clock pulses in binary. More |
| CPU (central processing unit) | The part of a computer that fetches instructions and carries them out. More |
| Current | The flow of charge, measured in amps. Its symbol is I. More |
| Cutoff frequency | Where a filter starts to cut: the signal is down to 70.7%, or −3 dB. More |
D
| Term | What it means |
|---|---|
| DC (direct current) | Current that flows one way at a steady voltage, as from a battery. More |
| Debounce | Ignoring the burst of on-off flickers a switch makes as its contacts settle. More |
| Decibel (dB) | A ratio on a log scale: 10 log for power and 20 log for voltage. −3 dB is half the power. More |
| Decoder | Logic that turns a binary code into one active line out of many. More |
| Decoupling capacitor | A small capacitor right beside a chip's supply pin that covers its sudden demands for current. More |
| De Morgan's laws | Two rules for flipping AND into OR: NOT (A · B) = Ā + B̄, and NOT (A + B) = Ā · B̄. More |
| Derivative (D term) | The part of a PID controller that pushes against how fast the error is changing. More |
| D flip-flop | A one-bit memory that copies its D input to its output on each clock edge. More |
| Differential drive | Steering with two wheels driven at different speeds, like a tank. More |
digitalRead() | The Arduino function that reads a pin as HIGH or LOW. More |
digitalWrite() | The Arduino function that sets a pin HIGH (5 V) or LOW (0 V). More |
| Diode | A part that lets current flow one way only, after a forward drop of about 0.7 V for silicon. More |
| Duty cycle | The share of each cycle a PWM signal spends on, as a percentage. More |
E
| Term | What it means |
|---|---|
| Edge | The moment a digital signal changes: a rising edge goes LOW to HIGH, a falling edge HIGH to LOW. More |
| Efficiency | The share of the power going in that comes out where you want it. The rest becomes heat. More |
| Electron | A tiny particle with negative charge. Electrons moving through a wire carry current. More |
| Emitter | The bipolar transistor terminal the current leaves by, on an NPN, usually wired to ground in a switch. More |
| Encoder | A sensor that gives a tick for each small turn of a wheel or shaft. More |
| Energy | The ability to do work, measured in joules. Power is how fast it's used. More |
| Error | In control, the gap between where a system should be and where it is. More |
F
| Term | What it means |
|---|---|
| Farad (F) | The unit of capacitance. One farad is huge, so real parts are in µF, nF and pF. More |
| Feedback | Feeding part of an output back to the input, to correct it or to set a gain. More |
| Feedforward | Adding the push you know a system needs before any error shows up. More |
| Filter | A circuit or piece of code that passes some frequencies and cuts others. More |
| Flip-flop | A circuit that stores one bit and changes only on a clock edge. More |
| Flyback diode | A diode across a coil that gives its current somewhere to go at switch-off, so no spike. More |
| Forward voltage | The voltage a diode or LED drops when it conducts, about 0.7 V for silicon and 2–3.2 V for LEDs. More |
| Frequency | How many cycles a wave makes each second, in hertz. More |
| Full adder | Logic that adds three bits, A, B and a carry in, giving a sum and a carry out. More |
| Fuse | A thin link meant to melt and break the circuit before too much current does damage. More |
G
| Term | What it means |
|---|---|
| Gain | How many times bigger a circuit makes a signal, or how hard a controller pushes per unit of error. More |
| Gate (logic) | A circuit that does one logic job, like AND, OR or NOT, on 0s and 1s. More |
| Gate (MOSFET) | The MOSFET's control terminal. A voltage on it, not a current, turns the switch on. More |
| Gray code | A way of counting in binary where only one bit changes at each step. More |
| Ground | The point in a circuit called 0 V, that other voltages are measured from. More |
| Ground plane | A whole layer of copper on a PCB used as ground. More |
| Gyroscope | A sensor that measures how fast something is turning, in degrees per second. More |
H
| Term | What it means |
|---|---|
| Half adder | Logic that adds two bits, giving a sum (XOR) and a carry (AND). More |
| Harmonic | A whole-number multiple of a wave's frequency. A square wave is a sine plus its odd harmonics. More |
| Heatsink | A metal block with fins that carries heat away from a hot part. More |
| Henry (H) | The unit of inductance. More |
| Hertz (Hz) | The unit of frequency: one cycle per second. More |
| High-pass filter | A filter that passes high frequencies and blocks DC and the bass. More |
| Hysteresis | Two thresholds instead of one, so a noisy signal near the line can't make the output flicker. More |
I
| Term | What it means |
|---|---|
| IC (integrated circuit) | A whole circuit built on one small chip of silicon, like an op-amp or a microcontroller. |
| Impedance | Resistance and reactance combined, in ohms: how much a part opposes AC. Its symbol is Z. More |
| Inductance | How strongly a coil fights a change in its current, measured in henries. More |
| Inductor | A coil of wire that stores energy in a magnetic field and resists changes in current. More |
| Insulator | A material, like plastic or glass, that hardly lets charge flow. More |
| Integral (I term) | The part of a PID controller that adds up the error over time, to remove what's left over. More |
| Inverting amplifier | An op-amp circuit that makes a signal bigger and flips it upside down. More |
J
| Term | What it means |
|---|---|
| Joule (J) | The unit of energy. One watt for one second is one joule. More |
| Jump | A CPU instruction that makes the program carry on from a different address, which is how loops work. More |
| Junction | A point where three or more wires meet, also called a node. More |
K
| Term | What it means |
|---|---|
| Kirchhoff's current law (KCL) | The current flowing into a junction equals the current flowing out. More |
| Kirchhoff's voltage law (KVL) | Round any loop, the voltage drops add up to the voltage rises. More |
| Kp, Ki and Kd | The three gains of a PID controller, for its P, I and D terms. More |
L
| Term | What it means |
|---|---|
| Latch | A simple one-bit memory that holds its state, set by one input and cleared by another. More |
| LC circuit | A coil and a capacitor together, which resonate at one frequency. More |
| LDR (light-dependent resistor) | A light sensor whose resistance falls as the light gets brighter. More |
| LED (light-emitting diode) | A diode that glows when current flows through it. It always needs something to limit that current, usually a resistor. More |
| Linear regulator | A chip that holds a steady output voltage by burning off the extra as heat. More |
| Lithium-ion | A rechargeable cell of about 3.7 V, used in phones and power banks. More |
| Load | The part of a circuit that uses the power, like a lamp or a motor. |
| Logic level | The voltage that counts as a 1 (HIGH) or a 0 (LOW). More |
loop() | The Arduino function that runs over and over, forever, after setup(). More |
| Low-pass filter | A filter that passes low frequencies and cuts high ones. More |
M
| Term | What it means |
|---|---|
| mAh (milliamp-hour) | A battery's capacity: 2000 mAh can supply 100 mA for about 20 hours. More |
map() | The Arduino function that rescales a number from one range to another, like 0–1023 to 0–255. More |
| Maximum power point | The voltage at which a solar panel delivers the most power. More |
| Microcontroller | A small computer on one chip, with memory and pins, that runs one program to control things. More |
millis() | The Arduino function that gives the milliseconds since the board started, for timing without stopping. More |
| Modulation | Changing a carrier wave to carry information, by its height (AM) or its frequency (FM, FSK). More |
| MOSFET | A transistor switched by the voltage on its gate. A logic-level one switches fully on from a 5 V pin. More |
| Moving average | Smoothing noisy readings by averaging the last few. More |
| Multimeter | A meter that measures voltage, current and resistance. More |
N
| Term | What it means |
|---|---|
| NAND gate | AND followed by NOT. Every other gate can be built from NANDs. More |
| Negative feedback | Feeding an output back so it opposes the input, which makes a circuit steady and its gain set. More |
| Non-inverting amplifier | An op-amp circuit that makes a signal bigger and keeps it the right way up. More |
| NOR gate | OR followed by NOT: the output is 1 only when every input is 0. More |
| NOT gate | A gate with one input that gives the opposite: 1 becomes 0 and 0 becomes 1. Also called an inverter. More |
| NPN | The common type of bipolar transistor, switched on by current into its base. More |
| Nyquist rate | Twice a signal's highest frequency. Sample faster than this to capture it truly. More |
O
| Term | What it means |
|---|---|
| Ohm (Ω) | The unit of resistance. One volt pushes one amp through one ohm. More |
| Ohm's law | V = I × R: voltage equals current times resistance. More |
| Op-amp (operational amplifier) | A chip with a huge gain that amplifies the difference between its two inputs. Feedback sets what it does. More |
| Open circuit | A break in the loop, so no current can flow. More |
| Open loop | Control that sets an output and never checks the result. More |
| OR gate | A gate whose output is 1 when any input is 1. More |
| Oscillator | A circuit that makes a repeating wave on its own. More |
| Overshoot | Going past the target before settling, often from too much gain. More |
P
| Term | What it means |
|---|---|
| Parallel | Parts connected side by side, so each gets the same voltage and the current splits. More |
| PCB (printed circuit board) | A board with copper traces that connect parts soldered onto it. More |
| Peak and peak-to-peak | A wave's height from the centre line to the top, and from the bottom to the top. More |
| Period | How long one cycle of a wave takes. It's 1 ÷ frequency. More |
| Phase | How far one wave is shifted from another in time, in degrees: 360° is a whole cycle. More |
| PID controller | A controller that adds three pushes: one for the error (P), its total (I) and its rate of change (D). More |
| PNP | A bipolar transistor that is the mirror of an NPN, switched on by pulling current out of its base. More |
| Potentiometer | A resistor with a sliding contact, which makes an adjustable voltage divider. More |
| Power | How fast energy is used or turned into heat, measured in watts: P = V × I. More |
| Power rating | The most power a part can safely turn into heat, like 0.25 W for a small resistor. More |
| Program counter | The CPU register that holds the address of the next instruction. More |
| Proportional control | Pushing in proportion to the error: big error, big push. More |
| Pull-down resistor | A resistor that holds an input at LOW until something drives it HIGH. More |
| Pull-up resistor | A resistor that holds an input at HIGH until a button or switch pulls it LOW. More |
| PWM (pulse-width modulation) | Switching a pin on and off fast, so the share of time it's on sets the average power. More |
Q
| Term | What it means |
|---|---|
| Q factor | How sharp a tuned circuit is: its centre frequency divided by its bandwidth. More |
R
| Term | What it means |
|---|---|
| RC circuit | A resistor and a capacitor together, used for timing and filtering. More |
| Reactance | How much a capacitor or coil opposes AC, in ohms. It changes with frequency. More |
| Rectifier | Diodes that turn AC into DC. More |
| Register | A row of flip-flops that holds a binary number, changing only when told to load. More |
| Regulator | A circuit that holds a supply at a steady voltage while the input or load changes. More |
| Relay | A switch worked by an electromagnet, so a small current can switch a big one. More |
| Resistance | How much a material or part opposes current, measured in ohms. More |
| Resistor | A part made to have a set resistance, marked with coloured bands. More |
| Resonance | When a coil and a capacitor swap energy back and forth at one natural frequency. More |
| Ripple | The small leftover wobble on a DC supply. More |
| RMS (root mean square) | The steady DC voltage that would heat a resistor the same as an AC one: a sine's peak ÷ √2. More |
| ROM (read-only memory) | Memory whose contents are fixed and can only be read. More |
S
| Term | What it means |
|---|---|
| Sample rate | How many readings are taken each second. More |
| Saturation | A transistor turned fully on, so it acts like a closed switch. More |
| Schmitt trigger | A comparator with hysteresis, which turns a slow or noisy signal into clean switching. More |
| Schottky diode | A diode with a lower forward drop, about 0.3 V, which wastes less power. More |
| Sequential logic | Logic with memory, whose outputs depend on what happened before as well as on its inputs now. More |
| Series | Parts connected end to end in one path, so the same current flows through each. More |
| Setpoint | The target a control loop is trying to reach. More |
setup() | The Arduino function that runs once at the start, to set up pins and settings. More |
| Shift register | A chain of flip-flops that moves bits along one place on each clock, like the 74HC595. More |
| Short circuit | An unintended path with almost no resistance, which lets a dangerous current flow. More |
| Sideband | The extra frequencies just above and below a carrier that hold a modulated signal. More |
| Sine wave | The smooth, regular wave shape of mains AC and of a pure tone. More |
| SR latch | A latch with a Set input and a Reset input, often made from two NOR gates. More |
| Star grounding | Running every ground wire back to one point, so currents don't share a path. More |
| State machine | Code or logic that is always in one of a few named states and moves between them on events. More |
T
| Term | What it means |
|---|---|
| T flip-flop | A flip-flop that toggles its output on each clock edge while T is 1. More |
| Thermal relief | Thin copper spokes joining a pad to a plane, so the pad is easier to solder. More |
| Thermal resistance | How much a part's temperature rises per watt of heat, in °C/W. More |
| Thermistor | A resistor whose resistance changes with temperature, used as a temperature sensor. More |
| Thevenin equivalent | Any network of sources and resistors seen from two terminals as one voltage behind one resistor. More |
| Time constant (τ) | How long an RC or RL circuit takes to get 63% of the way to its final value. More |
| Tolerance | How far a part's real value may be from its marked value, like ±5%. More |
| Trace | A copper track on a PCB that does the job of a wire. More |
| Transistor | A part that uses a small current or voltage to control a bigger current, as a switch or an amplifier. More |
| Truth table | A table of every input combination and the output each one gives. More |
| Two's complement | How computers store negative numbers: flip every bit and add 1. More |
V
| Term | What it means |
|---|---|
| Via | A plated hole that connects a trace on one layer of a PCB to another. More |
| Volt (V) | The unit of voltage: one joule of energy for each coulomb of charge. More |
| Voltage | The electrical push that makes charge flow, between two points. Its symbol is V. More |
| Voltage divider | Two resistors in series that give a set fraction of a voltage at their middle. More |
| Voltage drop | The voltage lost across a part or along a wire as current flows through it. More |
| Voltage follower | An op-amp wired so its output copies its input, but can drive a load. More |
W
| Term | What it means |
|---|---|
| Watt (W) | The unit of power: one joule per second, or one volt times one amp. More |
| Wavelength (λ) | The distance one cycle of a radio wave covers: 300 ÷ the frequency in MHz gives metres. More |
X
| Term | What it means |
|---|---|
| XNOR gate | A gate whose output is 1 when its inputs match, used to compare bits. More |
| XOR gate | Exclusive OR: the output is 1 when exactly one of two inputs is 1. More |
Z
| Term | What it means |
|---|---|
| Zener diode | A diode made to conduct backwards at a set voltage, used to hold a voltage steady. More |
Free lesson
Now build it yourself
Each lesson comes in three short parts: see the idea, try it on a live board, then build it yourself, with quick checks as you go.
Try it yourself: free lesson
“What is electricity?” is lesson 1 of 6 in Copper Flats, Electronics World 1. No account needed: start playing now.
The ideas behind it
- What is electricity?Charge on the move: conductors, insulators and why a circuit has to go all the way round.
- What is voltage?The push that makes charge flow: what a volt is, and why stacked cells add up.
- What is electric current?How much charge flows past a point each second, in amps, and why it's the same all round a loop.
- What is resistance?The squeeze on the flow, in ohms: how resistors set the current and protect an LED.
Questions people ask
What is the difference between voltage and current?
Voltage is the push that drives charge round a circuit, measured in volts. Current is how much charge flows past a point each second, measured in amps. A battery sets the voltage; the circuit's resistance then decides the current.
What do k, M, m and µ mean in front of a unit?
They're powers of ten. k (kilo) is a thousand, M (mega) a million, m (milli) a thousandth, µ (micro) a millionth, n (nano) a billionth and p (pico) a trillionth. So 4.7 kΩ is 4,700 Ω and 20 mA is 0.02 A.
What is the difference between AC and DC?
DC flows one way at a steady voltage, as from a battery. AC keeps reversing, usually as a sine wave, 50 or 60 times a second from a mains socket. Most electronics run on DC, so a power supply turns the mains into it.
More charts
- Standard resistor values chartThe E12, E24 and E96 series, decade by decade, and which one to reach for.
- SMD resistor code chartTurn 472, 4702, 4R7 or 01C on a tiny resistor into ohms.
- LED forward voltage by colourEach colour's forward voltage, and how many LEDs fit in series on 5 V, 9 V or 12 V.
- Electronics unit prefixes and conversionsp, n, µ, m, k, M and G, conversion tables, and what 4k7 or 2n2 means.
- Capacitor code chartTurn 104, 473J or 2A into a value, a tolerance and a voltage rating.
- Common diodes chart1N4148, 1N4007, 1N5819 and the 1N47xx Zeners compared, and which one to use.
- Common transistors chartRatings, gain and pinouts for the BJTs and MOSFETs in every parts kit.
- Logic gate truth tablesAll seven gates' truth tables, how to write each one, and the chip numbers to buy.
- Arduino Uno pins and limitsWhich Uno pin does what, and how much current each pin and the whole board can give.
- Binary, decimal and hex table0 to 15 in all three bases, the powers of two, common bytes, and converting four bits at a time.
- AWG wire gauge chartAWG and mm² side by side, ohms per metre, and roughly how many amps each size takes.
- Battery voltage and capacity chartFull, nominal and flat voltages, typical mAh, and how full a lithium cell is from its voltage.
- Electronics formulas cheat sheetOhm's law to antenna length: every formula in the course, what it gives and where to learn it.