Understanding Resistors

Resistors are fundamental electronic components that limit current flow in a circuit. They're characterized by their resistance value (measured in ohms, Ω), power rating (watts), and tolerance (percentage variation).

Series Resistors

When resistors are connected in series (end-to-end), their resistances add up: Rtotal = R1 + R2 + R3 + ...The same current flows through all resistors, but voltage divides proportionally.

Parallel Resistors

When resistors are connected in parallel (same two nodes), the total resistance is always less than the smallest individual resistor:1/Rtotal = 1/R1 + 1/R2 + 1/R3 + ...For two resistors: Rtotal = (R1 × R2) / (R1 + R2).

Resistor Color Code

Through-hole resistors use colored bands to indicate their value:

• 4-band: 2 digits + multiplier + tolerance
• 5-band: 3 digits + multiplier + tolerance
• Color mnemonic: Black Brown Red Orange Yellow Green Blue Violet Gray White (0-9)

SMD Resistor Codes

Surface-mount resistors use numeric codes:

• 3-digit: 103 = 10 × 10³ = 10kΩ
• 4-digit: 4702 = 470 × 10² = 47kΩ
• R notation: 4R7 = 4.7Ω, R47 = 0.47Ω

Voltage Dividers

A voltage divider uses two resistors to produce a lower output voltage from a higher input voltage. The formula is:Vout = Vin × R2 / (R1 + R2)This is commonly used for sensor interfaces and reference voltages.

Standard Resistor Values (E12 Series)

The E12 series provides 12 values per decade with 10% tolerance: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 (then 100, 120, 150... and so on)