Project Overview

This comprehensive guide demonstrates how to interface a 4-digit 7-segment display with a Raspberry Pi Pico microcontroller using the Wokwi online simulator. Learn to display numbers, create counters, show time, temperature readings, and build digital dashboard projects without any physical hardware.

What You'll Learn

7-segment display operation principles
Multiplexing technique for multi-digit displays
Raspberry Pi Pico GPIO control
MicroPython programming for displays
Counter and timer applications
Wokwi simulator for display projects

Components Required in Wokwi

Hardware (Virtual):

Diagram.json:

{
  "version": 1,
  "author": "Uri Shaked",
  "editor": "wokwi",
  "parts": [
    {
      "type": "wokwi-pi-pico",
      "id": "pico",
      "top": 65.16,
      "left": -27.77,
      "rotate": 90,
      "hide": false,
      "attrs": { "env": "arduino-community" }
    },
    {
      "type": "wokwi-7segment",
      "id": "sevseg1",
      "top": -21.97,
      "left": -85.69,
      "rotate": 0,
      "hide": false,
      "attrs": { "digits": "4" }
    }
  ],
  "connections": [
    [ "pico:GP0", "$serialMonitor:RX", "", [] ],
    [ "pico:GP1", "$serialMonitor:TX", "", [] ],
    [ "sevseg1:A", "pico:GP2", "green", [ "v-21", "h145", "v115", "h-68" ] ],
    [ "sevseg1:B", "pico:GP3", "green", [ "v-15", "h100", "v103", "h-65" ] ],
    [ "sevseg1:C", "pico:GP4", "green", [ "v16", "h37" ] ],
    [ "sevseg1:D", "pico:GP5", "green", [ "v22", "h53" ] ],
    [ "sevseg1:E", "pico:GP6", "green", [ "v32", "h42" ] ],
    [ "sevseg1:F", "pico:GP7", "green", [ "v-13", "h-96", "v116", "h104" ] ],
    [ "sevseg1:G", "pico:GP8", "green", [ "v11", "h1" ] ],
    [ "sevseg1:DP", "pico:GP9", "green", [ "v7", "h-3" ] ],
    [ "sevseg1:DIG1", "pico:GP10", "blue", [ "v-19", "h-84", "v128", "h81" ] ],
    [ "sevseg1:DIG2", "pico:GP11", "blue", [ "v-28", "h-121", "v144", "h80" ] ],
    [ "sevseg1:DIG3", "pico:GP12", "blue", [ "v-39", "h-139", "v162", "h79" ] ],
    [ "sevseg1:DIG4", "pico:GP13", "blue", [ "v66", "h-82" ] ]
  ]
}

1x Raspberry Pi Pico board
1x 4-Digit 7-Segment Display (Common Cathode)
4x Current-limiting resistors (220Ω-330Ω) - optional in simulation
Jumper wires (automatic in Wokwi)

Software:

MicroPython firmware
7-segment display library

Understanding 7-Segment Displays

What is a 7-Segment Display?

A 7-segment display uses seven LED segments (labeled A-G) plus a decimal point to show digits 0-9 and some letters.

Segment Mapping:

A = Top horizontal
B = Top right vertical
C = Bottom right vertical
D = Bottom horizontal
E = Bottom left vertical
F = Top left vertical
G = Middle horizontal
DP = Decimal point

Segment pio.h:

// -------------------------------------------------- //
// This file is autogenerated by pioasm; do not edit! //
// -------------------------------------------------- //

#pragma once

#if !PICO_NO_HARDWARE
#include "hardware/pio.h"
#endif

// ------- //
// segment //
// ------- //

#define segment_wrap_target 0
#define segment_wrap 5

static const uint16_t segment_program_instructions[] = {
            //     .wrap_target
    0x8080, //  0: pull   noblock         side 0     
    0xa027, //  1: mov    x, osr          side 0     
    0x6208, //  2: out    pins, 8         side 1     
    0x6408, //  3: out    pins, 8         side 2     
    0x6808, //  4: out    pins, 8         side 4     
    0x7008, //  5: out    pins, 8         side 8     
            //     .wrap
};

#if !PICO_NO_HARDWARE
static const struct pio_program segment_program = {
    .instructions = segment_program_instructions,
    .length = 6,
    .origin = -1,
};

static inline pio_sm_config segment_program_get_default_config(uint offset) {
    pio_sm_config c = pio_get_default_sm_config();
    sm_config_set_wrap(&c, offset + segment_wrap_target, offset + segment_wrap);
    sm_config_set_sideset(&c, 4, false, false);
    return c;
}

#include "hardware/clocks.h"
static inline void segment_program_init(PIO pio, uint sm, uint offset, uint first_segment_pin, uint first_digit_pin) {
    const int segment_pins = 8;
    const int digit_pins = 4;

    // Machine configuration: out pins, sideset pins, and shift direction.
    pio_sm_config c = segment_program_get_default_config(offset);
    sm_config_set_out_pins(&c, first_segment_pin, segment_pins);
    sm_config_set_sideset_pins(&c, first_digit_pin);
    sm_config_set_out_shift(&c, false, false, 32); // Shift to the left

    // Attach all pins to the PIO peripheral
    for (int pin = first_segment_pin; pin < first_segment_pin + segment_pins; pin++) {
        pio_gpio_init(pio, pin);
    }
    for (int pin = first_digit_pin; pin < first_digit_pin + digit_pins; pin++) {
        pio_gpio_init(pio, pin);
    }

    // Configure all pins as outputs
    pio_sm_set_consecutive_pindirs(pio, sm, first_segment_pin, segment_pins, true);
    pio_sm_set_consecutive_pindirs(pio, sm, first_digit_pin, digit_pins, true);

    // Run at 2000Hz:
    float div = (float)clock_get_hz(clk_sys) / 2000; 
    sm_config_set_clkdiv(&c, div);

    // Start the machine
    pio_sm_init(pio, sm, offset, &c);
    pio_sm_set_enabled(pio, sm, true);
}

#endif

Common Cathode vs Common Anode

Common Cathode (this tutorial uses this type):

All cathodes connected together to GND
Segments light up when pin is HIGH (3.3V)
More common and easier to use

Common Anode:

All anodes connected together to VCC
Segments light up when pin is LOW (0V)

4-Digit Display Multiplexing

A 4-digit display has:

8 segment pins (A, B, C, D, E, F, G, DP)
4 digit select pins (D1, D2, D3, D4)

Multiplexing Concept: Only one digit is active at a time, but switching happens so fast (>50 Hz) that all digits appear to be on simultaneously due to persistence of vision.

How it works:

Enable Digit 1, display its segments, disable
Enable Digit 2, display its segments, disable
Enable Digit 3, display its segments, disable
Enable Digit 4, display its segments, disable
Repeat cycle continuously

Step-by-Step Wokwi Setup Instructions

Step 1: Create New Raspberry Pi Pico Project

Navigate to https://wokwi.com
Click "New Project"
Select "Raspberry Pi Pico"
Pico board appears on canvas

Step 2: Add 4-Digit 7-Segment Display

Click the blue "+" (Add Part) button
Search for "7-segment" or "4-digit"
Select "4-Digit 7-Segment Display" or "TM1637"
Place it above the Pico board

Note: Wokwi may have different display modules. Look for common cathode 4-digit displays.

Step 3: Understanding Pin Configuration

4-Digit 7-Segment Display Pins:

Segment Pins (8 pins):

A, B, C, D, E, F, G, DP (Decimal Point)

Digit Select Pins (4 pins):

D1 (Digit 1 - leftmost)
D2 (Digit 2)
D3 (Digit 3)
D4 (Digit 4 - rightmost)

Total: 12 pins (8 segment + 4 digit select)

Step 4: Pin Assignment Strategy

To control the display efficiently, we'll use:

Segment Pins → GPIO Pins:

Segment	GPIO Pin	Description
A	GPIO 2	Top segment
B	GPIO 3	Top-right segment
C	GPIO 4	Bottom-right segment
D	GPIO 5	Bottom segment
E	GPIO 6	Bottom-left segment
F	GPIO 7	Top-left segment
G	GPIO 8	Middle segment
DP	GPIO 9	Decimal point

Digit Select Pins → GPIO Pins:

Digit	GPIO Pin	Position
D1	GPIO 10	Leftmost digit
D2	GPIO 11	Second digit
D3	GPIO 12	Third digit
D4	GPIO 13	Rightmost digit

Common Connection:

All digit cathodes → Pico GND (for common cathode)

Step 5: Wire the Circuit in Wokwi

Segment Connections (Blue/Green wires):

Display A → Pico GPIO 2
Display B → Pico GPIO 3
Display C → Pico GPIO 4
Display D → Pico GPIO 5
Display E → Pico GPIO 6
Display F → Pico GPIO 7
Display G → Pico GPIO 8
Display DP → Pico GPIO 9

Digit Select Connections (Blue wires):

Display D1 → Pico GPIO 10
Display D2 → Pico GPIO 11
Display D3 → Pico GPIO 12
Display D4 → Pico GPIO 13

Ground Connection:

Display GND (common cathode) → Pico GND

Wokwi Tips:

Click each display pin and drag to corresponding Pico GPIO
Wokwi auto-assigns wire colors
Hover over pins to see labels
Use zoom controls for precision

CODE:

/**
 * Pi Pico PIO driving a 4-digit seven segment display example.
 *
 * Copyright (C) 2021, Uri Shaked
 */

#include "segment.pio.h"

uint8_t digits[] = {
  0b11000000, // 0
  0b11111001, // 1
  0b10100100, // 2 
  0b10110000, // 3
  0b10011001, // 4
  0b10010010, // 5
  0b10000010, // 6
  0b11111000, // 7
  0b10000000, // 8
  0b10011000, // 9
};

const uint8_t first_segment_pin = 2;
const uint8_t first_digit_pin = 10;

void setup() {
  Serial1.begin(115200);
  Serial1.println("Raspberry Pi Pico PIO 7-Segment Example");

  // Load the PIO program and initialize the machine
  auto offset = pio_add_program(pio0, &segment_program);
  segment_program_init(pio0, 0, offset, first_segment_pin, first_digit_pin);
}

void displayNumber(uint value) {
  pio_sm_put(pio0, 0, 
    digits[value / 1000 % 10] << 24 |
    digits[value / 100 % 10] << 16 |
    digits[value / 10 % 10] << 8 |
    digits[value % 10]
  );
}

int i = 0;
void loop() {
  displayNumber(i++);
  delay(200);
}

Step 9: Run the Simulation

Click green "Start Simulation" play button
Watch all four digits light up showing "0000"
See counter increment automatically
Observe decimal point in demo 2
Check Serial Monitor for demo progression

Expected Display Output:

First demo: 0000 → 0001 → 0002 → ... → 0099

Second demo: 00.0 → 01.0 → 02.0 → ... → 99.0
Third demo: 0010 → 0009 → 0008 → ... → 0000
Fourth demo: 1234 (static)
Fifth demo: Continuous counting

Step 10: Verify Display Operation

Visual Checks:

All four digits should be visible simultaneously
Numbers should be clear and bright
No flickering (refresh rate is adequate)
Decimal points work when enabled
Transitions are smooth

Serial Monitor:

7-Segment Display Test Starting...

Demo 1: Counting 0-9999
Demo 2: Decimal numbers
Demo 3: Countdown from 10
Demo 4: Display 1234
Demo 5: Continuous counter

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How to Display Numbers on 4-Digit 7-Segment Display with Raspberry Pi Pico in Wokwi - Complete Step-by-Step Tutorial