How to Use LED: Two Pin (red): Examples, Pinouts, and Specs

A Light Emitting Diode (LED) is a semiconductor device that emits light when an electric current passes through it. The two-pin red LED is a specific type of LED that produces red light and is commonly used in electronics for indicators, displays, and illumination. Due to its simplicity and low power consumption, it is widely used in various applications such as power-on status indicators, traffic lights, and decorative lighting.

• Forward Voltage (Vf): Typically 1.8V to 2.2V
• Maximum Forward Current (If): 20mA (recommended operating current is 10-15mA)
• Luminous Intensity: Dependent on current and manufacturer, typically around 500-600 mcd
• Peak Wavelength: Approximately 625-630 nm (red)
• Viewing Angle: Typically 120 degrees

1. Identify the Anode and Cathode: The longer lead is usually the anode (positive), and the shorter lead is the cathode (negative). The flat side of the LED lens also indicates the cathode side.
2. Current Limiting Resistor: Always use a current-limiting resistor in series with the LED to prevent it from drawing excessive current. The value of the resistor can be calculated using Ohm's Law: R = (Vsupply - Vf) / If.
3. Polarity: Ensure that the LED is connected with the correct polarity, with the anode to the positive voltage and the cathode to the ground.
4. Soldering: When soldering the LED, avoid excessive heat and prolonged soldering time to prevent damage.

• Do not exceed the maximum forward current and voltage ratings.
• Use a resistor with a power rating that can handle the power dissipation.
• When using multiple LEDs, connect them in parallel with individual resistors for uniform brightness.

// Define the pin connected to the LED
const int ledPin = 13; // Most Arduino UNO boards have an onboard LED on pin 13

void setup() {
  pinMode(ledPin, OUTPUT); // Set the LED pin as an output
}

void loop() {
  digitalWrite(ledPin, HIGH); // Turn on the LED
  delay(1000);                // Wait for 1 second
  digitalWrite(ledPin, LOW);  // Turn off the LED
  delay(1000);                // Wait for 1 second
}

• LED Not Lighting Up: Check the polarity of the LED and ensure the current-limiting resistor is correctly calculated and installed.
• Dim LED: The current may be too low; verify the resistor value and the power supply voltage.
• LED Burnt Out: The current may have exceeded the maximum rating, or the polarity may have been reversed.

• Double-check the polarity of the LED before powering the circuit.
• Use a multimeter to measure the voltage across the LED and the current through the circuit.
• Ensure the power supply is stable and within the recommended voltage range.

Q: Can I connect the LED directly to a 5V supply? A: No, you should always use a current-limiting resistor to prevent damage to the LED.

Q: How do I calculate the resistor value for a 5V Arduino output? A: Using Ohm's Law, R = (Vsupply - Vf) / If. For a 5V supply and a typical red LED, R = (5V - 2V) / 0.015A ≈ 200Ω. A standard 220Ω resistor is a common choice.

Q: Can I use PWM to dim the LED? A: Yes, you can use pulse-width modulation (PWM) on a digital pin of the Arduino to control the brightness of the LED.

This documentation provides a comprehensive guide to using a two-pin red LED in electronic circuits. Always follow the technical specifications and best practices to ensure the longevity and proper functioning of the LED.