How to Use LED Red/Green: Examples, Pinouts, and Specs

The Red/Green LED is a versatile light-emitting diode capable of emitting either red or green light, depending on the polarity of the applied voltage. This dual-color LED is commonly used in electronic circuits as an indicator, status light, or part of a display system. Its compact size, low power consumption, and ability to display two colors make it ideal for applications requiring simple visual feedback.

• Power and status indicators
• Signal and error notifications
• Multi-state displays
• Educational and hobbyist projects
• Embedded systems and microcontroller-based circuits

Below are the key technical details for a typical Red/Green LED. Note that exact values may vary slightly depending on the manufacturer.

The Red/Green LED typically has two pins, as shown in the table below:

Note: Some Red/Green LEDs may have three pins (common cathode or common anode). Refer to the specific datasheet for details.

1. Determine the Polarity:

   • For a two-pin Red/Green LED, the color depends on the direction of current flow:
     • Forward bias (current flows from anode to cathode): Red light.
     • Reverse bias (current flows from cathode to anode): Green light.
   • For a three-pin LED, connect the common pin (anode or cathode) and control the other two pins to select the color.

2. Use a Current-Limiting Resistor:

   • Always connect a resistor in series with the LED to limit the current and prevent damage.
   • Calculate the resistor value using Ohm's Law:
     [ R = \frac{V_{supply} - V_{forward}}{I_{forward}} ] Example: For a 5V supply and a forward voltage of 2V (red), with a desired current of 20mA:
     [ R = \frac{5V - 2V}{0.02A} = 150\Omega ]

3. Connect to a Microcontroller (e.g., Arduino UNO):

   • Use a digital output pin to control the LED.
   • Use two GPIO pins for a two-pin LED to toggle between red and green.

The following code demonstrates how to control a two-pin Red/Green LED with an Arduino UNO:

// Define the pins connected to the LED
const int redPin = 9;  // Pin for red light (forward bias)
const int greenPin = 10; // Pin for green light (reverse bias)

void setup() {
  // Set the LED pins as outputs
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
}

void loop() {
  // Turn on the red light
  digitalWrite(redPin, HIGH);
  digitalWrite(greenPin, LOW); // Ensure green is off
  delay(1000); // Keep red on for 1 second

  // Turn on the green light
  digitalWrite(redPin, LOW); // Ensure red is off
  digitalWrite(greenPin, HIGH);
  delay(1000); // Keep green on for 1 second
}

• Polarity Matters: Incorrect polarity can prevent the LED from lighting up.
• Avoid Overcurrent: Exceeding the maximum current rating can permanently damage the LED.
• Use Proper Resistors: Always calculate and use the correct resistor value for your circuit.

1. The LED Does Not Light Up:

   • Check the polarity of the connections.
   • Ensure the current-limiting resistor is not too large.
   • Verify that the power supply voltage is sufficient.

2. The LED Is Dim:

   • The resistor value may be too high, reducing the current.
   • Check the supply voltage and ensure it meets the LED's forward voltage requirements.

3. The LED Flickers:

   • This may occur if the power supply is unstable.
   • Ensure proper connections and a stable voltage source.

4. The LED Only Lights Up in One Color:

   • For a two-pin LED, verify that the polarity is being reversed correctly.
   • For a three-pin LED, check the connections to the control pins.

Q: Can I use the Red/Green LED without a resistor?
A: No, a resistor is essential to limit the current and prevent damage to the LED.

Q: How do I know which pin is the anode or cathode?
A: For a two-pin LED, the longer leg is typically the anode (positive). If the legs are trimmed, refer to the flat edge on the LED casing, which usually indicates the cathode.

Q: Can I control the LED with PWM?
A: Yes, you can use PWM (Pulse Width Modulation) to adjust the brightness of each color by controlling the duty cycle of the signal.

Q: What happens if I exceed the maximum current rating?
A: Exceeding the current rating can cause the LED to overheat and fail permanently.

By following this documentation, you can effectively use a Red/Green LED in your electronic projects!