Resistors
resistors limit current and set voltages. unit: ohm (Ω). power rating: watt (W).
rule of thumb: 1/4 W through-hole is fine for most breadboard projects. if it gets warm, size up.
ohm’s law trio
V = I × R I = V / R R = V / I
series vs parallel
- series:
Rt = R1 + R2 + … - parallel:
1/Rt = 1/R1 + 1/R2 + …
color code (4-band)
| color | digit | multiplier | tolerance |
|---|---|---|---|
| black | 0 | ×100 | — |
| brown | 1 | ×101 | ±1% |
| red | 2 | ×102 | ±2% |
| orange | 3 | ×103 | — |
| yellow | 4 | ×104 | — |
| green | 5 | ×105 | ±0.5% |
| blue | 6 | ×106 | ±0.25% |
| violet | 7 | ×107 | ±0.1% |
| gray | 8 | ×108 | ±0.05% |
| white | 9 | ×109 | — |
| gold | — | ×10−1 | ±5% |
| silver | — | ×10−2 | ±10% |
power check
use P = I²R or P = VI. pick a wattage rating higher than your calculated power (add headroom).