🔢 Build a 2-Digit 7-Segment Display Counter with Raspberry Pi Pico

An easy electronics project for students

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🧠 What You’ll Learn

• What a 7-segment display is
• How to control it using Raspberry Pi Pico
• How to display numbers from 00 to 99
• How to write and run MicroPython code for the counter

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🧰 Materials Required

Item	Quantity
Raspberry Pi Pico	1
Breadboard	1
2 x 7-Segment Common Cathode Display	1
Jumper wires (Male–Male)	20+
Resistors (220Ω)	8 (optional but recommended)
USB cable for Pico	1
Computer with Thonny IDE	1

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🔎 What is a 7-Segment Display?

A 7-segment display is a component made up of 7 LEDs (labeled a–g) plus a dot (dp). You can control each segment using GPIO pins to show numbers and some letters.

Two types exist:

• Common Cathode: All LEDs share a GND pin, segments light up when the pin is set to HIGH.
• Common Anode: All LEDs share a +V pin, segments light up when the pin is set to LOW.

In this project, we’re using a common cathode display.

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🔌 Wiring Diagram

🧩 Segment Connections (shared for both digits)

Segment	GPIO Pin
a	GP0
b	GP1
c	GP2
d	GP3
e	GP4
f	GP5
g	GP6
dp	GP7

🧩 Digit Selection Pins

Display	Common Cathode Pin	GPIO
Left	COM1	GP16
Right	COM2	GP17

Tip: Use resistors (220Ω) between GPIOs and segment pins to avoid damaging the Pico.

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💻 The Python Code

Open Thonny IDE, connect your Pico, and paste the following code:

from machine import Pin
import utime

# Segment pins: a to dp → GPIO 0 to 7
segment_pins = [0, 1, 2, 3, 4, 5, 6, 7]
segments = [Pin(pin, Pin.OUT) for pin in segment_pins]

# Digit control pins → GPIO 16 and 17
digit_pins = [Pin(16, Pin.OUT), Pin(17, Pin.OUT)]  # 0 = ON

# Segment patterns for 0–9 (1 = ON for common cathode)
digit_patterns = [
    (1, 1, 1, 1, 1, 1, 0, 0),  # 0
    (0, 1, 1, 0, 0, 0, 0, 0),  # 1
    (1, 1, 0, 1, 1, 0, 1, 0),  # 2
    (1, 1, 1, 1, 0, 0, 1, 0),  # 3
    (0, 1, 1, 0, 0, 1, 1, 0),  # 4
    (1, 0, 1, 1, 0, 1, 1, 0),  # 5
    (1, 0, 1, 1, 1, 1, 1, 0),  # 6
    (1, 1, 1, 0, 0, 0, 0, 0),  # 7
    (1, 1, 1, 1, 1, 1, 1, 0),  # 8
    (1, 1, 1, 1, 0, 1, 1, 0)   # 9
]

# Show a digit on either display
def display_digit(display_index, number):
    # Turn off both displays before updating
    digit_pins[0].value(1)
    digit_pins[1].value(1)

    # Set segment pattern
    pattern = digit_patterns[number]
    for seg, val in zip(segments, pattern):
        seg.value(val)

    # Enable the selected display
    digit_pins[display_index].value(0)
    utime.sleep_us(500)
    digit_pins[display_index].value(1)

# Main loop: count from 00 to 99 quickly
while True:
    for tens in range(10):
        for ones in range(10):
            start = utime.ticks_ms()
            while utime.ticks_diff(utime.ticks_ms(), start) < 100:  # Speed control
                display_digit(0, tens)
                display_digit(1, ones)

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🎯 What Happens?

• Your display will count from 00 to 99 quickly.
• The code refreshes each digit very fast using multiplexing.
• The count is controlled by a 100 ms delay for each number.

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🧪 Try This!

• Change 100 to 50 to make it even faster!
• Modify the segment pattern to create custom letters (e.g., H, E, L, P)

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🔍 Code Explanation – Step by Step

Let’s break down the code into small parts so you understand what each part does:

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🔹 1. Import Libraries and Set Pins

pythonCopyEditfrom machine import Pin
import utime

• machine lets you control GPIO pins.
• utime is used for delays to control timing.

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🔹 2. Setup Segment Pins

pythonCopyEditsegment_pins = [0, 1, 2, 3, 4, 5, 6, 7]
segments = [Pin(pin, Pin.OUT) for pin in segment_pins]

• We’re using GPIO 0 to 7 to control segments a to dp.
• segments is a list of pins set as outputs.

💡 These pins will send HIGH (1) or LOW (0) to turn segments ON or OFF.

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🔹 3. Setup Display Selection Pins

pythonCopyEditdigit_pins = [Pin(16, Pin.OUT), Pin(17, Pin.OUT)]  # 0 = ON

• These two GPIOs (16 and 17) control which 7-segment display is active.
• Only one display is turned ON at a time using multiplexing.

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🔹 4. Digit Patterns for 0–9

pythonCopyEditdigit_patterns = [
    (1, 1, 1, 1, 1, 1, 0, 0),  # 0
    (0, 1, 1, 0, 0, 0, 0, 0),  # 1
    ...
]

• Each number has a specific segment combination.
• 1 means the segment is ON, 0 is OFF (because we use a common cathode display).

For example, to show 0, all segments except g and dp are ON.

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🔹 5. Function to Display One Digit

pythonCopyEditdef display_digit(display_index, number):
    digit_pins[0].value(1)
    digit_pins[1].value(1)

• Turns both displays OFF before starting — this avoids ghosting or overlapping numbers.

pythonCopyEdit    pattern = digit_patterns[number]
    for seg, val in zip(segments, pattern):
        seg.value(val)

• Applies the pattern (which segments to turn on) for the given digit.

pythonCopyEdit    digit_pins[display_index].value(0)
    utime.sleep_us(500)
    digit_pins[display_index].value(1)

• Turns ON the selected display (0 = ON).
• Waits a tiny bit (500 µs) so the digit stays visible.
• Then turns it OFF again.

💡 This function is called many times per second to simulate both digits being on.

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🔹 6. Main Counter Loop

pythonCopyEditwhile True:
    for tens in range(10):
        for ones in range(10):

• Loops from 00 to 99 using nested loops for tens and ones digits.

pythonCopyEdit            start = utime.ticks_ms()
            while utime.ticks_diff(utime.ticks_ms(), start) < 100:
                display_digit(0, tens)
                display_digit(1, ones)

• For every number (like 42), the digits 4 and 2 are displayed repeatedly for 100 milliseconds.
• This refreshes the digits fast enough to appear stable to your eyes.

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🎯 Summary

Part of Code	What It Does
segment_pins	Set GPIOs for segments a–dp
digit_pins	Control which digit is active
digit_patterns	Tell which segments to light for 0–9
display_digit()	Lights up one digit at a time
while True loop	Counts from 00 to 99 on repeat

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✅ Bonus Tip:

Want to show only one number (like temperature or score)?
Just change the code to update only when a value changes, not continuously loop.

🛠️ Troubleshooting Tips

Issue	Solution
Only one display lights	Check common pins (GP16/GP17) and grounding
Numbers look garbled	Make sure segment pins are wired in correct order
Segments are dim	Use external power and proper resistors

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🌟 Conclusion

This project is a great way to learn how microcontrollers communicate with displays. Once you’ve mastered this, you can go further by adding:

• Buttons to manually increase the count
• Displaying temperature or sensor data
• Converting it into a mini stopwatch or timer