Understanding Resistor Color Codes

• Resistor color coding is a system for indicating resistor values using colored bands
• Predominantly used for axial resistors due to their compact size

Standard Color Bands

• Most resistors feature four bands, but some utilize five or six
• Bands indicate the resistor's value, tolerance, and sometimes the temperature coefficient

Color Code Table

• Colors represent specific digits:
  • Black: 0
  • Brown: 1
  • Red: 2
  • Orange: 3
  • Yellow: 4
  • Green: 5
  • Blue: 6
  • Violet: 7
  • Gray: 8
  • White: 9
• Gold and Silver denote tolerance:
  • Gold: 5%
  • Silver: 10%
  • No color: 20%

Four-Band Resistors

• The first two bands indicate the first two digits of the resistance value
• The third band serves as the multiplier, a power of ten
• The fourth band specifies the tolerance

Calculation Example (Four-Band)

• A resistor with Brown, Black, Red, and Gold bands
  • Brown (1), Black (0), Red (10^2 or 100), Gold (5%)
  • Resistance equals 10 * 100 = 1000 ohms
  • Tolerance is 5%
  • Final value: 1000 ohms ± 5%

Five-Band Resistors

• The first three bands represent the first three digits
• The fourth band is the multiplier
• The fifth band indicates the tolerance

Calculation Example (Five-Band)

• A resistor with Red, Red, Black, Brown, and Red bands
  • Red (2), Red (2), Black (0), Brown (10^1 or 10), Red (2%)
  • Resistance equals 220 * 10 = 2200 ohms
  • Tolerance is 2%
  • Final value: 2200 ohms ± 2%

Six-Band Resistors

• Similar to five-band resistors but includes an additional band
• The sixth band specifies the temperature coefficient in ppm/K (parts per million per Kelvin)
  • Black: 250 ppm/K
  • Brown: 100 ppm/K
  • Red: 50 ppm/K
  • Orange: 15 ppm/K
  • Yellow: 25 ppm/K
  • Green: 20 ppm/K
  • Blue: 10 ppm/K
  • Violet: 5 ppm/K
  • Gray: 1 ppm/K

Calculation Example (Six-Band)

• A resistor with Red, Red, Black, Brown, Red, Brown bands
  • Red (2), Red (2), Black (0), Brown (10^1 or 10), Red (2%), Brown (100 ppm/K)
  • Resistance = 220 * 10 = 2200 ohms
  • Tolerance = 2%
  • Temperature Coefficient = 100 ppm/K
  • Final value: 2200 ohms ± 2%, 100 ppm/K

Preferred Values

• Resistor values often come from a set of designated "preferred values"
• These values ensure a suitable range of resistances with tolerance

E Series

• E6 (20% tolerance): 1.0, 1.5, 2.2, 3.3, 4.7, 6.8
• E12 (10% tolerance): 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2
• E24 (5% tolerance): 1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1
• E48 (2% tolerance)
• E96 (1% tolerance)
• E192 (0.5%, 0.25%, 0.1% tolerance)

Reading Resistors

• Identify the side with bands closest to the edge and read from that side
• The tolerance band (gold or silver) is usually the last band

Zero-Ohm Resistors

• Resistance of essentially zero ohms
• Functions as jumpers on circuit boards
• Typically marked with a single black band

Special Cases

• Older or specialized resistors might employ different color codes or markings
• Always consult the manufacturer's datasheet if unsure

Temperature Coefficient

• Indicates the resistance value change per degree Celsius (or Kelvin)
• A lower coefficient means greater stability

Power Rating

• Indicates the maximum power a resistor can dissipate safely
• Power rating is determined by the size and type, not the color code

Limitations

• Small resistors may have hard to read color codes
• Color perception varies, leading to errors
• Digital multimeters offer a more accurate resistance measurement