How to Use MAX7219 8 Digit 7 Segment: Examples, Pinouts, and Specs

The MAX7219 from Maxim Integrated is a compact, serial input/output common-cathode display driver that can interface microcontrollers to 7-segment numeric LED displays of up to 8 digits. Its primary function is to convert a serial input to parallel outputs for LED display. It is widely used in applications such as digital clocks, electronic meters, and other devices that require numeric displays.

• 10MHz Serial Interface
• Individual LED segment control
• Drive common-cathode LED display up to 8 digits
• 150μA low-power shutdown (data retained)
• Digital brightness control
• Display-blanked on power-up
• Drive 7-segment digits and/or discrete LEDs

• Supply Voltage (V): +4.0V to +5.5V
• Supply Current (I): 330μA
• Operating Temperature Range: -40°C to +85°C

1. Connect V+ and GND to the power supply (4.0V to 5.5V).
2. Connect DIN, CS, and CLK to the microcontroller's SPI pins.
3. Connect ISET to a resistor to set the segment current.
4. Connect the DIG and SEG pins to the 7-segment display.

To control the MAX7219, send data serially using the SPI protocol. The data consists of a 4-bit register address and an 8-bit data byte.

#include <SPI.h>

// Define the connections to the MAX7219
#define CS_PIN  10

void setup() {
  // Set the CS pin as an output
  pinMode(CS_PIN, OUTPUT);
  // Begin SPI
  SPI.begin();
  // Initialize the MAX7219
  max7219Init();
}

void loop() {
  // Update display with some value
  max7219DisplayNumber(12345678);
}

void max7219Init() {
  // Set the number of digits to use
  max7219SendData(0x0B, 0x07);
  // Use normal operation mode
  max7219SendData(0x0C, 0x01);
  // Set the intensity (brightness) of the display
  max7219SendData(0x0A, 0x08);
  // No decode for the digits
  max7219SendData(0x09, 0x00);
}

void max7219SendData(byte registerAddress, byte data) {
  // Enable the CS pin
  digitalWrite(CS_PIN, LOW);
  // Send the register address
  SPI.transfer(registerAddress);
  // Send the data
  SPI.transfer(data);
  // Disable the CS pin
  digitalWrite(CS_PIN, HIGH);
}

void max7219DisplayNumber(long number) {
  // Display each digit of the number
  for (int i = 0; i < 8; i++) {
    byte digit = number % 10;
    max7219SendData(i + 1, digit);
    number /= 10;
  }
}

• Use a current-limiting resistor with ISET to prevent damage to the LEDs.
• Ensure that the power supply voltage is within the specified range.
• Avoid sending data to the MAX7219 while the display is being updated to prevent flickering.

• Display not lighting up: Check the power supply connections and the current-limiting resistor on ISET.
• Garbled display: Ensure that the SPI data is being sent correctly and that there is no noise on the communication lines.
• Dim display: Adjust the brightness control register or check the current-limiting resistor.

Q: Can the MAX7219 drive other types of LEDs? A: Yes, it can drive discrete LEDs in addition to 7-segment displays.

Q: How do I control the brightness of the display? A: Use the intensity register (0x0A) to adjust the brightness level.

Q: Can I daisy-chain multiple MAX7219s? A: Yes, you can connect the DOUT of one MAX7219 to the DIN of the next and control multiple devices with a single microcontroller.

For further assistance, consult the MAX7219 datasheet provided by Maxim Integrated.