5.2 Number Display¶
7 Segment Display can be seen everywhere in life. For example, on an air conditioner, it can be used to display temperature; on a traffic indicator, it can be used to display a timer.
The 7 Segment Display is essentially a device packaged by 8 LEDs, of which 7 strip-shaped LEDs form an “8” shape, and there is a slightly smaller dotted LED as a decimal point. These LEDs are marked as a, b, c, d, e, f, g, and dp. They have their own anode pins and share cathodes. Their pin locations are shown in the figure below.
This means that it needs to be controlled by 8 digital signals at the same time to fully work and the 74HC595 can do this.
Schematic
Here the wiring principle is basically the same as 5.1 Microchip - 74HC595, the only difference is that Q0-Q7 are connected to the a ~ g pins of the 7 Segment Display.
74HC595 |
LED Segment Display |
---|---|
Q0 |
a |
Q1 |
b |
Q2 |
c |
Q3 |
d |
Q4 |
e |
Q5 |
f |
Q6 |
g |
Q7 |
dp |
Wiring
Code
Note
Open the
5.2_number_display.py
file under the path ofeuler-kit/micropython
or copy this code into Thonny, then click “Run Current Script” or simply press F5 to run it.Don’t forget to click on the “MicroPython (Raspberry Pi Pico)” interpreter in the bottom right corner.
For detailed tutorials, please refer to Open and Run Code Directly.
import machine
import time
SEGCODE = [0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f]
sdi = machine.Pin(0,machine.Pin.OUT)
rclk = machine.Pin(1,machine.Pin.OUT)
srclk = machine.Pin(2,machine.Pin.OUT)
def hc595_shift(dat):
rclk.low()
time.sleep_ms(5)
for bit in range(7, -1, -1):
srclk.low()
time.sleep_ms(5)
value = 1 & (dat >> bit)
sdi.value(value)
time.sleep_ms(5)
srclk.high()
time.sleep_ms(5)
time.sleep_ms(5)
rclk.high()
time.sleep_ms(5)
while True:
for num in range(10):
hc595_shift(SEGCODE[num])
time.sleep_ms(500)
When the program is running, you will be able to see the LED Segment Display display 0~9 in sequence.
How it works?
hc595_shift()
will make 74HC595 output 8 digital signals.
It outputs the last bit of the binary number to Q0, and the output of the first bit to Q7. In other words, writing the binary number “00000001” will make Q0 output high level and Q1~Q7 output low level.
Suppose that the 7-segment Display display the number “1”, we need to write a high level for b, c, and write a low level for a, d, e, f, g, and dg.
That is, the binary number “00000110” needs to be written. For readability, we will use hexadecimal notation as “0x06”.
Similarly, we can also make the LED Segment Display display other numbers in the same way. The following table shows the codes corresponding to these numbers.
Numbers |
Binary Code |
Hex Code |
---|---|---|
0 |
00111111 |
0x3f |
1 |
00000110 |
0x06 |
2 |
01011011 |
0x5b |
3 |
01001111 |
0x4f |
4 |
01100110 |
0x66 |
5 |
01101101 |
0x6d |
6 |
01111101 |
0x7d |
7 |
00000111 |
0x07 |
8 |
01111111 |
0x7f |
9 |
01101111 |
0x6f |
Write these codes into hc595_shift()
to make the LED Segment Display display the corresponding numbers.