Arduino and MAX7219, 8 Digit, 7 Segment BCD Counter

In Embedded system design, seven segment displays are playing a major role as numerical visual indications. Seven segment LED displays are brighter, more attractive and provide a far viewing distance as well as a wider viewing angle as compared to LCD displays. Its available wide dimensions (0.3 inch to 6 inch) and different colors (RED, GREEN, BLUE, ORANGE, WHITE). It can display digits from 0 to 9 and quite a few characters like A, b, C, d, E, e, F, n, o, P, t, u, etc. This intractable is about interfacing 8 digits of 7 segment display by using popular MAX7219 display driver with Arduino Uno.

Parts and components

• Arduino Uno board
• Max7219 4 Digit 7Segment Common cathode displays = 2 Nos
• Or Max7219 assembled board

• The MAX7219 display driver chip provides a 3-wire serial (SPI) interface to drive 7-segment LED displays (common-cathode type) up to 8 digits.
• The on-chip includes a BCD decoder, multiplex scan circuitry, segment and digit drivers, and an 8×8 static RAM to store the digit values.
• The DIN, LOAD and CLOCK pins of MAX7219 is connected with 4,3 and 2 digital IO pins of Arduino.
• Two (RED and BLUE) 4 digit, common cathode seven segment displays are connected to the drive pins on MAX7219.
• Otherwise, one can use the pre-assembled MAX7219 board with 8 digits, and connect the drive pins accordingly.

• The Arduino LedControl library is used for displaying digits on MAX7219.
• The count variable updated by one count, at every 500mS.
• The count_one variable which is duplicate of count, will be converted into BCD, and displayed at the 4,5,6 and 7th digits.
• The count_two variable which is multiplication 7 of count, will be converted into BCD, and displayed at the 1,2,3 and 4th digits.
• The count will be reset to zero once it reaches 9999.

Conclusion

• The project is successfully simulated by using the Proteus.
• The MAX7219 can be used for many embedded projects as numerical display.

/*
 Demonstrates
the use of MAX7219 and 2 of 4x7 Segment display.
 The Arduino
circuit connection for 7219:
 * MAX7219
DIN pin to digital pin 4
 * MAX7219
LOAD pin to digital pin 3
 * MAX7219
CLOCK pin to digital pin 2
 * 
 Name:-
M.Pugazhendi
 Date:-  05thJul2016
 Version:-
V0.1
 e-mail:-
muthuswamy.pugazhendi@gmail.com
*/
#include 
// inputs: DIN pin, CLK pin, LOAD pin. number of
chips
LedControl mydisplay = LedControl(4, 2, 3, 1);
unsigned int count = 0;
unsigned int count_one = 0;
unsigned int count_two = 0;
void setup() 
{
 
mydisplay.shutdown(0, false);  //
turns on display
 
mydisplay.setIntensity(0, 15); // 15 = brightest
 
mydisplay.setDigit(0, 0, 9, false);
 
mydisplay.setDigit(0, 1, 8, false);
 
mydisplay.setDigit(0, 2, 7, false);
 
mydisplay.setDigit(0, 3, 6, false);
 
mydisplay.setDigit(0, 4, 5, true);
 
mydisplay.setDigit(0, 5, 4, false);
 
mydisplay.setDigit(0, 6, 3, false);
 
mydisplay.setDigit(0, 7, 2, false);
}
void loop() 
{
  count++;
 
if((count*7) >= 9999)
  {
    count =
0;
  }
  count_one =
HexToBCD(count);
  count_two =
HexToBCD(count*7); 
 
mydisplay.setDigit(0, 0, ((count_two>>12)&0x0F), false);
 
mydisplay.setDigit(0, 1, ((count_two>>8)&0x0F), false);
 
mydisplay.setDigit(0, 2, ((count_two>>4)&0x0F), false);
 
mydisplay.setDigit(0, 3, ((count_two>>0)&0x0F), false);
 
mydisplay.setDigit(0, 4, ((count_one>>12)&0x0F), false);
 
mydisplay.setDigit(0, 5, ((count_one>>8)&0x0F), false);
 
mydisplay.setDigit(0, 6, ((count_one>>4)&0x0F), false);
 
mydisplay.setDigit(0, 7, (count_one&0x0F), false);
  delay(500);
}
/**************************************************************************
*!
 * \brief
Coverts hex into BCD
 *
 * This
function will coverts hex into BCD
 *
 * \param[in]
byte
 *
\param[out] byte
 * \return
Nill
 * 
 *
**************************************************************************/
unsigned int HexToBCD(unsigned int number)
{
    unsigned
char i=0;
    unsigned
int k = 0;
   
while(number)
    {
        k = (
k ) | ((number%10) << i*4);
       
number = number / 10;
        i++;
    }
   
return(k);
}