Controlling Eight 7-Segment LED Displays

In this project, you'll learn how to connect and control eight 7-segment LED displays using the MAX7219 driver chip.

In the 7-segment LED display tutorial, you learned how to control one 7-segment LED display. In order to control more 7-segment LED displays you will need to use a dedicated LED driver chip such as the MAX7219. One MAX7219 driver chip allows you to easily control one to eight 7-segment LED displays. Furthermore, you can daisy chain eight MAX7219 chips together, each one controlling eight 7-segment displays, giving you a total of 64 7-segment LED displays!

Parts needed:
  • Arduino
  • A 3-, 4-, or 8-digit 7-Segment Common Cathode LED display
  • MAX7219 LED driver chip
  • A 22KΩ (red-red-orange) resistor
  • A 0.1uF (104) capacitor
  • Wires
  • Breadboard

  • You also need to download the LedControl software library which contains all of the functions for interfacing with the MAX7219 LED driver chip.
Arduino      3x7-Segment LED display      4x7-Segment LED display      8x7-Segment LED display      MAX7219 LED driver chip      22KΩ resistor      0.1uF capacitor     
1 Making the connections

If your LED display is already connected to the MAX7219 chip, then skip this step and go to step 2.

Otherwise, you need to make the following connections between the MAX7219 chip and your 7-segment LED display. The pinouts for the MAX7219 chip and 4-digit 7-segment LED display are shown on the right.

Use the pin connections under either the Three 7-segment or Four 7-segment column depending on whether you have a 3-digit or 4-digit display.

MAX7219 Three 7-segment Four 7-segment Description
2 8 (Common Cathode) 6 (Common Cathode) Digit 0 (rightmost digit)
11 9 (Common Cathode) 8 (Common Cathode) Digit 1
6 12 (Common Cathode) 9 (Common Cathode) Digit 2
7 12 (Common Cathode) Digit 3
14 11 11 Segment A
15 10 10 Segment F
16 7 7 Segment B
17 5 5 Segment G
20 4 4 Segment C
21 1 1 Segment E
22 3 3 Segment DP
23 2 2 Segment D
MAX7219 pinouts

        4-digit 7-segment pins


In addition, you need to make the following two connections on the MAX7219 chip:
  • Connect a 22KΩ (red-red-orange) resistor between pin 18 (ISET) and pin 19 (V+).
  • Connect a 0.1uF (104) capacitor between pin 4 (GND) and pin 19 (V+).
22KΩ resistor      0.1uF capacitor     
2 The MAX7219 chip requires five connections to the Arduino: DIN, CS, CLK, V+ and GND.

MAX7219 Arduino Description
1 12 DIN
12 11 CS
13 10 CLK
19 5V V+
9 GND GND
3 Download and save the LedControl library. Do not open it.
4 Install the LedControl library by selecting Sketch from the Arduino IDE menu
  • then select Import Library or Include Library
  • then select Add Library or Add .ZIP Library
Locate and select the LedControl.zip file that you just downloaded in step 3. It should be in the Download folder.

Click click the Open button

(Refer to this document for more information on how to install a library if you run into problems.)
5 Create a new program by selecting File from the menu
  • then select Examples
  • then select LedControl
  • then select _7segment
6 Upload and run the program.

Refer to the LedControl library reference documentation for details on how to use the functions in this library.

Experiments

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