What is a Resistor?
A resistor is a passive electronic component that resists the flow of current in a circuit. Its value is measured in ohms (Ω). Beginners use resistors to protect LEDs, divide voltage, pull inputs high or low, and set current in transistor circuits.
How a resistor works
Ohm's law (V = I × R) governs a resistor. Applying voltage V across a resistor of R ohms causes current I = V/R to flow. Energy dissipates as heat.
Common resistor values in projects
You'll use these constantly:
- 220 Ω — LED current limiting on 5 V
- 330 Ω — LED current limiting on higher voltages
- 1 kΩ — pull-down for buttons, transistor base
- 10 kΩ — pull-up resistor for inputs, I2C pull-ups
- 4.7 kΩ — DHT sensor data line pull-up
Reading the colour code
Most through-hole resistors have 4 or 5 colour bands. Read from the end closest to a band: first digits, multiplier, tolerance. Print or memorise a chart — it's the fastest skill you'll ever pick up.
FAQs
Does resistor polarity matter?
No. Resistors work in either direction.
Why is my LED still burning out?
You're likely using too small a resistor or none at all. Use 220 Ω for a red LED on 5 V.
