Table of Contents
Choosing the correct resistor value for LED indicators in Arduino circuits is essential to ensure proper operation and prevent damage to the LED or the microcontroller. This article explains how to calculate the appropriate resistor value based on the LED’s specifications and the power supply voltage.
Understanding the Components
An LED (Light Emitting Diode) requires a current-limiting resistor to prevent excessive current flow. The Arduino typically supplies 5V or 3.3V, depending on the model. The resistor value depends on the LED’s forward voltage and desired current.
Calculating the Resistor Value
The basic formula to determine the resistor value is:
R = (V_supply – V_f) / I
Where:
- R = Resistor value in ohms (Ω)
- V_supply = Supply voltage from Arduino (e.g., 5V)
- V_f = Forward voltage of the LED (typically 2V for red LEDs)
- I = Desired current through the LED (commonly 20mA or 0.02A)
For example, with a 5V supply, a red LED with a forward voltage of 2V, and a desired current of 20mA:
R = (5V – 2V) / 0.02A = 150Ω
Choosing Standard Resistor Values
Resistor values are available in standard series. If the calculated value is not available, select the next higher standard value to ensure the LED is protected. For example, if 150Ω is not available, choose 220Ω.
Additional Tips
Always verify the LED’s specifications before calculations. Using a resistor with too low a value can damage the LED or Arduino pin, while too high a value may result in a dim LED. Adjust the resistor value accordingly for different LED colors and brightness requirements.