How to use MAX7221 to drive 7-segment LED set using a micro

[Shane]

MAX7221 LED driver IC from Maxim is for driving either 64 individual Led's, or up to 8 digits of 7-segment displays. The driver implement a SPI compatible slave interface that can be controlled from the Arduino using only 3 of the digital output pins. An extensive datasheet for the IC is available from the Maxim homepage. Both MAX7219 and MAX7221 are very similar, we will use MAX7221 for the tutorial.

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Code: Select all

//USE SPI TO CONTROL THE MAX7221 LED DRIVER
 //THIS CODE EXAMPLES IMPLEMENTS A SIMPLE 4-DIGIT COUNTER

#define DATAOUT 11//MOSI
 #define DATAIN 12//MISO - not used, but part of builtin SPI
 #define SPICLOCK 13//sck
 #define SLAVESELECT 10//ss

byte digit=1;
 byte counterNumber1=0;
 byte counterNumber10 = 0;
 byte counterNumber100 = 0;
 byte counterNumber1000 = 0;

///////////////////////////////////////////////////////////////////
 //spi transfer function (from ATmega168 datasheet)
 char spi_transfer(volatile char data)
 {
 SPDR = data; // Start the transmission
 while (!(SPSR & (1<<SPIF))) // Wait the end of the transmission
 {
 };
 return SPDR; // return the received byte
 }

///////////////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////
 byte write_7seg(int digAddress, int displayValue) //dig pot data transfer function
 {
 digitalWrite(SLAVESELECT,LOW); //digital pot chip select is active low
 //2 byte data transfer to digital pot
 spi_transfer(digAddress);
 spi_transfer(displayValue);
 digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
 }

///////////////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////
 void setup()
 {
 byte i;
 byte clr;
 pinMode(DATAOUT, OUTPUT);
 pinMode(DATAIN, INPUT);
 pinMode(SPICLOCK,OUTPUT);
 pinMode(SLAVESELECT,OUTPUT);
 digitalWrite(SLAVESELECT,HIGH); //disable device

 ///////////////////////////////////////////////////////////////////
 // SPCR = 01010000
 //interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
 //sample on leading edge of clk,system clock/4 (fastest)
 SPCR = (1<<SPE)|(1<<MSTR);
 clr=SPSR;
 clr=SPDR;
 delay(10);
 ///////////////////////////////////////////////////////////////////

//clear 7221 and format to receive data
 write_7seg(0x0C,1);
 write_7seg(0x09,0xFF);
 write_7seg(0x0A,0x0F);
 write_7seg(0x0B,0x04);
 }

///////////////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////
 void loop()
 {
 do{
 write_7seg(1, counterNumber1000);
 counterNumber1000++;
 do{
 write_7seg(2, counterNumber100);
 counterNumber100++; 
 do{
 write_7seg(3, counterNumber10);
 counterNumber10++;
 do{
 write_7seg(4, counterNumber1);
 delay (100);
 counterNumber1++;
 }while (counterNumber1<10);
 counterNumber1 = 0;
 }while (counterNumber10<10);
 counterNumber10 = 0;
 }while (counterNumber100<10);
 counterNumber100 = 0;
 }while (counterNumber1000<10);
 counterNumber1000 = 0;
 }

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Matrix LED wiring diagram

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Courtecy of UMASS AMHERST