15. Chapter 74HC595 & 7-Segment Display

In this chapter, we will introduce the 7-Segment Display.

15.1. Project 7-Segment Display.

We will use 74HC595 to control 7-segment display and make it display hexadecimal character “0-F”.

15.1.1. Component List

ESP32-S3 WROOM x1		GPIO Extension Board x1
Breadboard x1
74HC595 x1	Resistor 220Ω x8		7-segment display x1
Jumper M/M

15.1.2. Component knowledge

15.1.2.1. 7-segment display

A 7-segment display is a digital electronic display device. There is a figure “8” and a decimal point represented, which consists of 8 LEDs. The LEDs have a common anode and individual cathodes. Its internal structure and pin designation diagram is shown below:

As we can see in the above circuit diagram, we can control the state of each LED separately. Also, by combining LEDs with different states of ON and OFF, we can display different characters (Numbers and Letters). For example, to display a “0”: we need to turn ON LED segments A, B, C, D, E and F, and turn OFF LED segments G and DP.

In this project, we will use a 7-Segment Display with a common anode. Therefore, when there is an input low level to a LED segment the LED will turn ON. Defining segment “A” as the lowest level and segment “DP” as the highest level, from high to low would look like this: “DP”, “G”, “F”, “E”, “D”, “C”, “B”, “A”. Character “0” corresponds to the code: 1100 0000b=0xc0.

For detailed code values, please refer to the following table (common anode).

CHAR	DP	G	F	E	D	C	B	A	Hex	ASCII
0	1	1	0	0	0	0	0	0	0xc0	1100 0000
1	1	1	1	1	1	0	0	1	0xf9	1111 1001
2	1	0	1	0	0	1	0	0	0xa4	1010 0100
3	1	0	1	1	0	0	0	0	0xb0	1011 0000
4	1	0	0	1	1	0	0	1	0x99	1001 1001
5	1	0	0	1	0	0	1	0	0x92	1001 0010
6	1	0	0	0	0	0	1	0	0x82	1000 0010
7	1	1	1	1	1	0	0	0	0xf8	1111 1000
8	1	0	0	0	0	0	0	0	0x80	1000 0000
9	1	0	0	1	0	0	0	0	0x90	1001 0000
A	1	0	0	0	1	0	0	0	0x88	1000 1000
B	1	0	0	0	0	0	1	1	0x83	1000 0011
C	1	1	0	0	0	1	1	0	0xc6	1100 0110
D	1	0	1	0	0	0	0	1	0xa1	1010 0001
E	1	0	0	0	0	1	1	0	0x86	1000 0110
F	1	0	0	0	1	1	1	0	0x8e	1000 1110

15.1.3. Circuit

Schematic diagram
Hardware connection. If you need any support, please contact us via: support@freenove.com

15.1.4. Code

In this section, the 74HC595 is used in the same way as in the previous section, but with different values transferred. We can learn how to master the digital display by sending the code value of “0” - “F”.

Move the program folder “Freenove_Ultimate_Starter_Kit_for_ESP32_S3/Python/Python_Codes” to disk(D) in advance with the path of “D:/Micropython_Codes”.

Open “Thonny”, click “This computer” -> “D:” -> “Micropython_Codes” -> “74HC595_and_7_segment_display”.

Select “my74HC595.py”, right click your mouse to select “Upload to /”, wait for “my74HC595.py” to be uploaded to ESP32-S3 and then double click“74HC595_and_7_segment_display.py”.

15.1.4.1. 74HC595_and_7_segment_display

Click “Run current script”, and you’ll see a 1-bit, 7-segment display displaying 0-f in a loop.

The following is the program code:

import time
from my74HC595 import Chip74HC595

lists =[0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8,
        0x80, 0x90, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e]

chip = Chip74HC595(12,13,14)
try:
    while True:
        for count in range(16):
            chip.shiftOut(0,lists[count])
            time.sleep_ms(500)
except:
    pass

Import time and my74HC595 modules.

import time
from my74HC595 import Chip74HC595

Put the encoding “ 0 “ - “ F “ into the list.

lists =[0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8,
        0x80, 0x90, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e]

Define an object, whose pins applys default configuration, to drive 74HC595.

chip = Chip74HC595(12,13,14)

Send data of digital tube to 74HC595 chip.

chip.shiftOut(0,lists[count])

15.2. Project 4-Digit 7-Segment Display

Now, let’s try to control more digit 7-segment display

15.2.1. Component List

ESP32-S3 WROOM x1		GPIO Extension Board x1
Breadboard x1
74HC595 x1	Resistor 220Ω x8		7-segment display x1
Jumper M/M

15.2.2. Component knowledge

15.2.2.1. 4 Digit 7-Segment Display

A 4 Digit 7-segment display integrates four 7-segment displays into one module, therefore it can display more characters. All of the LEDs contained have a common anode and individual cathodes. Its internal structure and pin designation diagram is shown below:

The internal electronic circuit is shown below, and all 8 LED cathode pins of each 7-segment display are connected together.

Display method of 4 digit 7-segment display is similar to 1 digit 7-segment display. The difference between them is that the 4-digit displays each Digit is visible in turn, one by one and not together. We need to first send high level to the common end of the first digit display, and send low level to the remaining three common ends, and then send content to 8 LED cathode pins of the first Digit Display. At this time, the first 7-segment display will show visible content and the remaining three will be OFF.

Similarly, the second, third and fourth 7-segment displays will show visible content in turn by scanning the display. Although the four number characters are displayed in turn separately, this process is so fast that it is imperceptible to the naked eye. This is due to the principle of optical afterglow effect and the vision persistence effect in human sight. This is how we can see all 4 number characters at the same time. However, if each number character is displayed for a longer period, you will be able to see that the number characters are displayed separately.

15.2.3. Circuit

Schematic diagram
Hardware connection. If you need any support, please contact us via: support@freenove.com

15.2.4. Code

In this code, we use the 74HC595 IC Chip to control the 4-Digit 7-Segment Display, and use the dynamic scanning method to show the changing number characters.

Open “Thonny”, click “This computer” -> “D:” -> “Micropython_Codes” -> “4_Digit_7_Segment_Display”. Select “my74HC595.py”, right click your mouse to select “Upload to /”, wait for “my74HC595.py” to be uploaded to ESP32-S3 and double click “4_Digit_7_Segment_Display.py”.

15.2.4.1. 4_Digit_7_Segment_Display

Click “Run current script”, and the Nixie tube display as shown in the image below.

The following is the program code:

import time
from my74HC595 import Chip74HC595
from machine import Pin

comPin=[47,35,36,21]
num =[0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8,
      0x80, 0x90, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e]

def led_display():
    for i in range(0,4):
        chns=Pin(comPin[i],Pin.OUT)
        chns.value(1)
        chip.shiftOut(0,num[i])
        time.sleep_ms(1)
        chns.value(0)
        chip.shiftOut(0,0xff)


#Pin(38)-74hc595.ds, Pin(39)-74hc595.st_cp, Pin(40)-74hc595.sh_cp
chip = Chip74HC595(38,39,40)
try:
    while True:
        led_display()
except:
    pass

Import time, my74HC595 and Pin modules.

import time
from my74HC595 import Chip74HC595
from machine import Pin

Define common anode pins for digital tubes and request a list to put character encodings in it.

comPin=[47,35,36,21]
num =[0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8,
      0x80, 0x90, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e]

Request an object to drive 74HC595 and associate pins with it.

chip = Chip74HC595(38,39,40)

Make the digital tube display “0123”.

def led_display():
    for i in range(0,4):
        chns=Pin(comPin[i],Pin.OUT)
        chns.value(1)
        chip.shiftOut(0,num[i])
        time.sleep_ms(1)
        chns.value(0)
        chip.shiftOut(0,0xff)