Ruggi.SiteElectronics cheat sheet
Component symbols, prefixes, E-series, resistor and capacitor markings, LED voltages, logic levels, common IC pinouts, Arduino Uno pins, bus signals, soldering temperatures and multimeter symbols on a printable page.
Component symbols
Two common styles exist for resistors (box or zigzag); this sheet uses the box. The long plate of a battery is positive.
Prefixes and units
V volt, A ampere, Ω ohm, W watt, F farad, H henry, Hz hertz, C coulomb, J joule, S siemens. Ohm: V = I·R. Power: P = V·I = I²·R = V²/R. Capacitor: Q = C·V. Frequency and period: f = 1/T.
E-series (preferred values)
Multiply by 10, 100, 1k ... Typical tolerance: E6 20%, E12 10%, E24 5%, E48 2%, E96 1%.
Resistor markings
4 bands: digit, digit, multiplier, tolerance. 5 bands: three digits, multiplier, tolerance. Example: yellow violet red gold = 47 × 100 = 4.7 kΩ, 5%. SMD: 103 = 10 kΩ, 472 = 4.7 kΩ, 4R7 = 4.7 Ω, 1002 = 10 kΩ; EIA-96 two digits + letter (01C = 10 kΩ), see the calculators and the colour-code tool.
Capacitor markings
| Ceramic 3-digit code (pF) | 104 = 100 nF, 103 = 10 nF, 473 = 47 nF, 102 = 1 nF, 222 = 2.2 nF, 101 = 100 pF |
| Tolerance letter | F 1%, G 2%, J 5%, K 10%, M 20%, Z +80/−20% |
| Dielectric | C0G/NP0 stable (±30 ppm/°C); X7R ±15% over −55 to +125 °C; X5R ±15% to +85 °C; Y5V large change, avoid for timing |
| Electrolytic | Stripe marks the negative lead; the longer lead of a new part is positive; rated voltage printed (use 25% or more margin) |
| Tantalum (SMD) | Stripe usually marks the positive end (typical; check the datasheet) |
LED forward voltage (typical, around 20 mA)
Check the datasheet. Resistor = (Vs − Vf) / I.
Logic levels (typical)
VIL max = highest voltage read as low; VIH min = lowest voltage read as high; VOL max / VOH min = guaranteed output levels. Margins: high = VOH − VIH, low = VIL − VOL. A 3.3 V output may not reach VIH of a 5 V CMOS (HC) input: use an HCT part or a level shifter. Never feed 5 V into a 3.3 V-only pin.
Common IC pinouts (top view, notch/dot at top, pin 1 top left)
| 555 timer, DIP-8 | |||
|---|---|---|---|
| 1 | GND | 8 | VCC |
| 2 | TRIGGER | 7 | DISCHARGE |
| 3 | OUTPUT | 6 | THRESHOLD |
| 4 | RESET | 5 | CONTROL |
| LM358 dual op-amp, DIP-8 | |||
|---|---|---|---|
| 1 | OUT A | 8 | V+ |
| 2 | IN A − | 7 | OUT B |
| 3 | IN A + | 6 | IN B − |
| 4 | V− / GND | 5 | IN B + |
| LM324 quad op-amp, DIP-14 | |||
|---|---|---|---|
| 1 | OUT 1 | 14 | OUT 4 |
| 2 | IN 1 − | 13 | IN 4 − |
| 3 | IN 1 + | 12 | IN 4 + |
| 4 | V+ | 11 | V− / GND |
| 5 | IN 2 + | 10 | IN 3 + |
| 6 | IN 2 − | 9 | IN 3 − |
| 7 | OUT 2 | 8 | OUT 3 |
| TO-220 (front = printed side facing you, legs down, left to right) | |
|---|---|
| 78xx (7805, 7812 ...) | 1 IN, 2 GND, 3 OUT (metal tab is GND) |
| LM317 | 1 ADJ, 2 OUT, 3 IN (metal tab is OUT) |
| Small transistors, TO-92 (flat face toward you, legs down, left to right) | |
|---|---|
| BC547 / BC337 style | C, B, E (typical) |
| 2N2222 / PN2222 plastic | E, B, C (typical; the metal-can 2N2222 differs) |
| Pin orders vary by maker and part: check the datasheet or use the multimeter diode test before powering. | |
Arduino Uno (ATmega328P) header
| Digital | D0 RX, D1 TX, D2 (INT0), D3 (INT1, PWM), D4, D5 (PWM), D6 (PWM), D7, D8, D9 (PWM), D10 (PWM, SS), D11 (PWM, MOSI), D12 (MISO), D13 (SCK, on-board LED) |
| Analog in | A0 - A5; A4 = SDA, A5 = SCL (I2C) |
| Power | 5V, 3.3V, VIN, GND (3 pins), IOREF, RESET, AREF |
| Levels | 5 V logic, 16 MHz; about 20 mA per pin is the usual working limit, 40 mA absolute maximum (typical figures; check the datasheet) |
Bus signal names
| I2C | SDA (data), SCL (clock), GND; pull-up resistors to Vdd; two wires for many devices |
| SPI | SCK (clock), MOSI / COPI (controller out), MISO / CIPO (controller in), CS / SS (chip select, one per device) |
| UART | TX of one side goes to RX of the other (crossed), common GND; same baud rate both sides (9600 and 115200 are typical) |
Trace width and PCB
Current-carrying trace width depends on copper weight, temperature rise and the standard used (IPC-2221 / IPC-2152). No numbers are given here; use the formulas or a calculator and see the PCB design starter. Wire gauge to current limits are code dependent and are deliberately not listed.
Soldering (typical)
Contact time about 2-4 s per joint; use the lowest tip temperature that makes a good joint; ventilate fumes. See the soldering and multimeter starter.