How to Use Adafruit 14-segment LED Alphanumeric Backpack Red: Examples, Pinouts, and Specs

The Adafruit 14-Segment LED Alphanumeric Backpack is a versatile and easy-to-use display module that allows users to add a bright, crisp red LED alphanumeric display to their projects. Each of the alphanumeric characters is made up of 14 segments that can be controlled individually to display letters, numbers, and a variety of symbols. This component is commonly used in clocks, counters, and readouts in various electronics projects.

• Digital clocks and timers
• Counter displays
• Message boards
• Electronic scoreboards
• User interfaces for various projects

• Display Color: Red
• Operating Voltage: 2.0V to 3.3V
• Forward Current (per segment): 18mA
• Peak Forward Current (per segment): 120mA
• Reverse Voltage (per segment): 5V

1. Power Connections: Connect the VCC pin to a 3.3V or 5V power supply and the GND pin to the ground.
2. Data Connections: Connect the SDA and SCL pins to the I2C data and clock lines on your microcontroller.
3. Address Selection: The backpack has solder jumpers for setting the I2C address. By default, it is set to 0x70.

• Ensure that the power supply voltage does not exceed the maximum rating of 5V.
• Limit the peak forward current to avoid damaging the LED segments.
• Use pull-up resistors on the I2C data lines if your microcontroller does not have built-in pull-ups.
• When daisy-chaining multiple backpacks, make sure to set unique I2C addresses for each one.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_LEDBackpack.h>

Adafruit_AlphaNum4 alpha4 = Adafruit_AlphaNum4();

void setup() {
  alpha4.begin(0x70);  // Initialize the display with its I2C address
}

void loop() {
  alpha4.writeDigitAscii(0, 'H');  // Display 'H' on the first character
  alpha4.writeDigitAscii(1, 'E');  // Display 'E' on the second character
  alpha4.writeDigitAscii(2, 'L');  // Display 'L' on the third character
  alpha4.writeDigitAscii(3, 'P');  // Display 'P' on the fourth character
  alpha4.writeDisplay();           // Send data to the display to show it
  delay(500);                      // Wait for half a second
  alpha4.clear();                  // Clear the display
  alpha4.writeDisplay();           // Send the clear command to the display
  delay(500);                      // Wait for half a second
}

• Display Not Lighting Up: Check the power connections and ensure the I2C address is correctly set.
• Garbled Characters: Ensure there are no loose connections and the I2C lines are connected properly.
• Dim Display: Make sure the forward current is within the specified range and not below the operating current.

• Double-check wiring, especially the I2C connections.
• Verify that the correct I2C address is being used in your code.
• If using multiple displays, ensure each one has a unique I2C address.
• Check for solder bridges on the address selection jumpers if the address was changed.

Q: Can I use this display with a 5V microcontroller like an Arduino UNO? A: Yes, the display can be used with a 5V microcontroller. However, ensure that the logic levels for I2C are compatible.

Q: How many of these displays can I chain together? A: You can chain up to eight displays by setting unique I2C addresses for each one using the address jumpers.

Q: Can I display custom characters? A: Yes, the display supports custom characters. You can create custom bitmaps for each segment to form your desired character.

Q: Is it necessary to use external resistors with this display? A: No, the display has built-in resistors for the LED segments. However, pull-up resistors for the I2C lines may be necessary depending on your microcontroller.