Go Down

Topic: (Solved) Need Assistance with Max7219 and 4 Digit 7 Segment LED (Read 1 time) previous topic - next topic


Nov 30, 2012, 03:36 am Last Edit: Nov 30, 2012, 04:03 am by SteveOr Reason: 1
I'm attempting to drive a 4 digit 7-segment LED using a MAX7219 shift register with the code below and schematic from 7.12 of the Arduino Cookbook.  It calls for the Max7221 but I thought I'd try it with a Max7219 (I'm new to this but I hope it doesn't make a difference with this simple sketch).  

Code: [Select]
#include <SPI.h> // Arduino SPI library introduced in Arduino version 0019
const int slaveSelect = 10; //pin used to enable the active slave
const int numberOfDigits = 2; // change these to match the number of digits wired up
const int maxCount = 99;
int number = 0;
void setup()
SPI.begin(); // initialize SPI
pinMode(slaveSelect, OUTPUT);
digitalWrite(slaveSelect,LOW); //select slave
// prepare the 7221 to display 7-segment data - see data sheet
sendCommand(12,1); // normal mode (default is shutdown mode);
sendCommand(15,0); // Display test off
sendCommand(10,8); // set medium intensity (range is 0-15)
sendCommand(11,numberOfDigits); // 7221 digit scan limit command
sendCommand(9,255); // decode command, use standard 7-segment digits
digitalWrite(slaveSelect,HIGH); //deselect slave
void loop()
// display a number from the serial port terminated by the end of line character
char ch = Serial.read();
if( ch == '\n')
number = 0;
number = (number * 10) + ch - '0'; // see Chapter 4 for details
// function to display up to four digits on a 7-segment display
void displayNumber( int number)
for(int i = 0; i < numberOfDigits; i++)
byte character = number % 10; // get the value of the rightmost decade
if(number == 0 && i > 0)
character = 0xf; // the 7221 will blank the segments when receiving value
// send digit number as command, first digit is command 1
sendCommand(numberOfDigits-i, character);
number = number / 10;
void sendCommand( int command, int value)
digitalWrite(slaveSelect,LOW); //chip select is active low
//2-byte data transfer to the 7221
digitalWrite(slaveSelect,HIGH); //release chip, signal end transfer

I believe I have set up the hardware correctly on my breadboard.  My problem is that nothing happens but more significantly is that the Arduino's on board LEDs all go dim.  When I disconnect the pins into ground or 5v the Arduino comes back to life.  I'm using 30 ohms for the resistor for the Max7219 per the table on this page:  http://arduino.cc/playground/Main/MAX72XXHardware#SelectRSet

I'm using this 4 digit 7 Segment LED: http://www.mouser.com/Search/ProductDetail.aspx?R=HDSP-B03Evirtualkey63050000virtualkey630-HDSP-B03E .   If someone can advise me where I went wrong I'd really appreciate it.

Edit:  Rookie mistake.  I had positive and negative jumpers reversed.

Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131