KEMI Docs
Electronics Basics
How to read resistor color bands, Ohm's law and power formulas, and capacitor marking codes — on one page. These are three representative sheets excerpted from the KEMI Electronics Reference Bundle (printable sheets); tables and figures are transcribed as published. Keep it open whenever you need to read a part in your hand.
Excerpt 1
Resistor Color Code
Hold the tolerance band (gold/silver) on the right, then read left to right.
| Color | Digit | Multiplier | Tolerance | Temp. coeff. (ppm/°C) |
|---|---|---|---|---|
| Black | 0 | ×10⁰ (1) | — | 250 (U) |
| Brown | 1 | ×10¹ | ±1% (F) | 100 (S) |
| Red | 2 | ×10² | ±2% (G) | 50 (R) |
| Orange | 3 | ×10³ | ±0.05% (W) | 15 (P) |
| Yellow | 4 | ×10⁴ | ±0.02% (P) | 25 (Q) |
| Green | 5 | ×10⁵ | ±0.5% (D) | 20 (Z) |
| Blue | 6 | ×10⁶ | ±0.25% (C) | 10 (Z) |
| Violet | 7 | ×10⁷ | ±0.1% (B) | 5 (M) |
| Grey | 8 | ×10⁸ | ±0.01% (L) | 1 (K) |
| White | 9 | ×10⁹ | — | — |
| Gold | — | ×10⁻¹ (0.1) | ±5% (J) | — |
| Silver | — | ×10⁻² (0.01) | ±10% (K) | — |
Examples
- · brn·blk·red·gold → 10×10² = 1 kΩ ±5%
- · yel·vio·org·gold → 47×10³ = 47 kΩ ±5%
- · red·red·blk·brn·brn → 220×10¹ = 2.2 kΩ ±1%
- · grn·blu·blk·sil → 56×10⁻² = 0.56 Ω ±10%
Mnemonic (0–9): Big Brown Rabbits Often Yield Great Big Vocal Groans
Standard values — E12 / E24 series
| Series | Values per decade (repeat at every ×10ⁿ) |
|---|---|
| E12 ±10% | 10 · 12 · 15 · 18 · 22 · 27 · 33 · 39 · 47 · 56 · 68 · 82 |
| E24 ±5% | all E12 + 11 · 13 · 16 · 20 · 24 · 30 · 36 · 43 · 51 · 62 · 75 · 91 |
e.g. E12 value 4.7 exists as 4.7 Ω, 47 Ω, 470 Ω, 4.7 kΩ, 47 kΩ … Gold/silver as the multiplier means a low-value resistor (under 1 Ω – under 10 Ω). A 0 Ω jumper resistor is a single black band.
Excerpt 2
Ohm's Law & Power
Memorize just these four — the other eight are rearrangements.
V voltage [V] · I current [A] · R resistance [Ω] · P power [W]. e.g. 50 mA through 220 Ω — voltage V = I·R = 0.05 × 220 = 11 V, power P = I²·R = 0.05² × 220 = 0.55 W.
Series & parallel combinations
A parallel combination is always smaller than the smallest resistor.
| Component | Series | Parallel | Memory hook |
|---|---|---|---|
| Resistor R | R = R₁ + R₂ + … | 1/R = 1/R₁ + 1/R₂ + … (two: R₁R₂/(R₁+R₂)) | series = bigger · parallel = smaller |
| Capacitor C | 1/C = 1/C₁ + 1/C₂ + … (two: C₁C₂/(C₁+C₂)) | C = C₁ + C₂ + … | opposite of resistors |
| Inductor L | L = L₁ + L₂ + … | 1/L = 1/L₁ + 1/L₂ + … | same as resistors |
Voltage & current dividers
Vout = Vin × R₂/(R₁+R₂)
The resistor you tap across (R₂) goes in the numerator. A load appears in parallel with R₂ and pulls Vout down → keep load ≫ R₂.
I₁ = Iin × R₂/(R₁+R₂)
Current favors the smaller resistance — the opposite resistor goes in the numerator. If R₁=R₂, it splits in half.
Quick table — voltage × resistance → current [mA]
I [mA] = V ÷ R [kΩ] · * = resistor dissipation P=V²/R exceeds 1/4 W
| V \ R | 100 Ω | 220 Ω | 330 Ω | 470 Ω | 1 kΩ | 4.7 kΩ | 10 kΩ |
|---|---|---|---|---|---|---|---|
| 3.3 V | 33 | 15.0 | 10.0 | 7.0 | 3.3 | 0.70 | 0.33 |
| 5 V | 50 | 22.7 | 15.2 | 10.6 | 5.0 | 1.06 | 0.50 |
| 12 V | 120 * | 54.5 * | 36.4 * | 25.5 * | 12.0 | 2.55 | 1.20 |
Example · LED series resistor
5 V supply, LED VF=2.0 V, want 10 mA: · Across the resistor: 5 − 2.0 = 3 V · R = V/I = 3/0.010 = 300 Ω (E24 value) · P = 0.010²×300 = 0.03 W → 1/4 W is fine 330 Ω still gives 9.1 mA — close enough for an LED
Unit tip
Convert to base units (V·A·Ω·W) first and you won't slip. Handy pairs: · V = mA × kΩ · mA = V ÷ kΩ · mW = mA × V · mW = mA² × kΩ e.g. 3.3 V ÷ 10 kΩ = 0.33 mA. Multiply mA by Ω directly and you're off by 1000×!
Excerpt 3
Capacitor Marking Codes
Value = first two digits × 10^(third digit) — always in pF. Conversion: 1 µF = 1,000 nF = 1,000,000 pF · 1 nF = 1,000 pF · 0.1 µF = 100 nF (104).
- · 104 K → 0.1 µF ±10% · 473 J → 47 nF ±5% · 225 M → 2.2 µF ±20%
- · Two digits = value as-is: 22 = 22 pF, 47 = 47 pF · R = decimal point (pF): 4R7 = 4.7 pF · Trailing 9 = ×0.1: 479 = 47×0.1 = 4.7 pF
Common codes → values
★ = most used in practice. Codes not listed follow the same rule
| Code | pF | nF | µF |
|---|---|---|---|
| 100 | 10 | 0.01 | — |
| 101 | 100 | 0.1 | — |
| 102 | 1,000 | 1 | 0.001 |
| 103 | 10,000 | 10 | 0.01 |
| 104 ★ | 100,000 | 100 | 0.1 |
| 105 | 1,000,000 | 1,000 | 1 |
| 220 | 22 | 0.022 | — |
| 221 | 220 | 0.22 | — |
| 222 | 2,200 | 2.2 | 0.0022 |
| 223 | 22,000 | 22 | 0.022 |
| 224 | 220,000 | 220 | 0.22 |
| 470 | 47 | 0.047 | — |
| 471 | 470 | 0.47 | — |
| 472 | 4,700 | 4.7 | 0.0047 |
| 473 | 47,000 | 47 | 0.047 |
| 474 | 470,000 | 470 | 0.47 |
Temperature characteristics — ceramic Class 1 / Class 2
| Code | Temp range | Cap. change | Recommended use |
|---|---|---|---|
| C0G/NP0 (Class 1) | −55~+125 °C | 0 ±30 ppm/°C | filters · osc. · timing (most stable) |
| X5R (Class 2) | −55~+85 °C | ±15% | general decoupling |
| X7R (Class 2) | −55~+125 °C | ±15% | general · power · automotive |
| Y5V (Class 2) | −30~+85 °C | +22/−82% | low-cost, not for precision |
Class 2 code rule — first letter = low limit (X: −55 / Y: −30 / Z: +10 °C) · digit = high limit (5: +85 / 6: +105 / 7: +125 / 8: +150 °C) · last letter = cap. change (R: ±15% / U: +22/−56% / V: +22/−82%).
Go-to values by use
| Use | Typical value | Preferred type |
|---|---|---|
| IC decoupling | 0.1 µF (104) | MLCC X7R·X5R |
| Supply bulk | 10–100 µF | MLCC · electrolytic |
| Crystal load | 12–22 pF | C0G/NP0 |
| Smoothing (post-rectifier) | 470–1000 µF | electrolytic |
| Coupling (audio) | 1–10 µF | film · electrolytic |
| Timing (RC · 555) | per circuit calc. | C0G · film (precise) |
Watch out
Class 2 ceramics (X5R·X7R·Y5V) lose much of their capacitance under DC bias — over −50% near rated voltage, worse in small packages. Allow generous margin in capacitance and voltage. Electrolytic and tantalum parts print the value directly (e.g. 470µF 25V); on aluminum the stripe marks the negative (−) lead, on tantalum the bar marks the positive (+) — opposite! Reversing destroys it.
This document is an excerpt
The full PDF editions of the Electronics Reference Bundle include SMD package size charts, pinouts (Uno · ESP32 · Raspberry Pi), soldering and multimeter guides, sensor · motor · wireless module references, a C syntax cheatsheet, plus practice worksheets — all as printable sheets.
Need this turned into a real circuit?
Send one line of requirements and KEMI carries it from platform choice to schematic, board and firmware.
Request circuit design →FAQ
What value is a capacitor marked 104?
Value = first two digits × 10^(third digit), always in pF. So 104 = 10×10⁴ pF = 100,000 pF = 100 nF = 0.1 µF. A trailing letter (e.g. K) is the tolerance — K means ±10%.
Which end of a resistor do I read from?
Hold the tolerance band (gold/silver) on the right and read left to right — the wider gap marks the tolerance side. On 5-band (±1%) parts the first three bands are digits. Measuring with a multimeter on the Ω range is definitive.
Is a 1/4 W resistor always enough?
No. Check the dissipation with P = I²R (or V²/R) and stay under 50% of the rating. For example, 5 V across 100 Ω is exactly 0.25 W — no margin on a 1/4 W part.
This document is an excerpt of KEMI's own reference material. Figures are representative values and may vary slightly by manufacturer — check the part datasheet for real designs. All trademarks mentioned are the property of their respective owners.