Charlieplexed LED Display Guide

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Below is the complete schematic update suggestion that incorporates 32 LED-resistor pairs arranged in a Charlieplex configuration using 7 designated I/O pins of the ATmega328. Each LED is the 0805 SMD type, and each resistor is an 0805 220Ω device. The wiring is arranged so that the resistor is placed on the side that will be driven HIGH and the LED’s cathode is connected to the pin that will be driven LOW, ensuring correct polarity.
Schematic Update Instructions:
  1. Microcontroller Setup:
    • Confirm an ATmega328 is present in the schematic.
    • Reserve 7 I/O pins (e.g., PD0, PD1, PD2, PD3, PD4, PD5, PD6) for the Charlieplex network.
  2. Adding LED-Resistor Pairs:
    • For each of the 32 channels (labeled LED1 to LED32 and R_LED1 to R_LED32):
      • Place an 0805 SMD LED: Use 0805 SMD LED.
      • Place an 0805 220Ω Resistor: Use 0805 Resistor (220Ω).
      • Connect the resistor and LED in series so that:
        • The resistor is connected to the microcontroller I/O pin that will be driven HIGH.
        • The LED’s anode is between the resistor and the LED, and the LED’s cathode goes to the second I/O pin that will be driven LOW.
  3. Charlieplex Wiring Pattern:
    • Distribute the 32 LED-resistor chains among the 7 I/O pins by connecting each pair between a unique ordered pair of pins.
    • During operation, to illuminate a chosen LED-resistor pair:
      • Set the “first” I/O pin (the one connected through the resistor) to OUTPUT HIGH.
      • Set the “second” I/O pin (the one connected to the LED’s cathode) to OUTPUT LOW.
      • Configure all remaining I/O pins as high impedance.
    • The firmware will be responsible for scanning these combinations quickly to create the logical 4×8 LED display.
  4. Verification and Labeling:
    • Label each pair clearly (e.g., LED1 with R_LED1, LED2 with R_LED2, …, LED32 with R_LED32).
    • Verify that every LED-resistor chain is assigned a unique I/O pair from the 7 available to ensure proper Charlieplex operation without conflicts.
    • Ensure the resistor is positioned to limit current appropriately based on the LED’s forward voltage characteristics.
You can now use the "Apply changes" button to incorporate these schematic update instructions into your project.
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