How to connect a 7 segment LCD to a STM32 microcontroller? - Blog

Connecting a 7-segment LCD to an STM32 microcontroller is a fundamental yet crucial task in electronics projects, whether it's for a simple digital clock or a more complex industrial control system. As a 7-segment LCD supplier, I've witnessed firsthand the importance of a seamless connection between these components. In this blog, I'll guide you through the process of connecting a 7-segment LCD to an STM32 microcontroller, from understanding the basics to troubleshooting common issues.

Understanding the Basics

Before we dive into the connection process, let's first understand the two main components involved: the 7-segment LCD and the STM32 microcontroller.

7-Segment LCD

A 7-segment LCD is a display device composed of seven individual segments arranged in the shape of the digit 8. Each segment can be illuminated independently to form different digits and some letters. There are two types of 7-segment LCDs: common cathode and common anode. In a common cathode 7-segment LCD, all the cathodes of the individual segments are connected together and grounded, while in a common anode 7-segment LCD, all the anodes are connected together and supplied with a positive voltage.

We offer a wide range of 7-segment LCDs, including VA LCD Display and TN LCD Panel. These displays are known for their high quality, excellent visibility, and long lifespan.

STM32 Microcontroller

The STM32 is a family of 32-bit microcontrollers based on the ARM Cortex-M processor. It offers a wide range of features and performance levels, making it suitable for a variety of applications. The STM32 microcontroller has multiple GPIO (General Purpose Input/Output) pins that can be used to control external devices such as the 7-segment LCD.

Connecting the 7-Segment LCD to the STM32 Microcontroller

Now that we have a basic understanding of the components, let's proceed with the connection process.

Step 1: Gather the Required Components

7-segment LCD (either common cathode or common anode)
STM32 microcontroller (e.g., STM32F103C8T6)
Breadboard
Jumper wires
Resistors (to limit the current flowing through the segments)

Step 2: Identify the Pins

The 7-segment LCD has a total of 10 pins: 7 pins for the individual segments (a, b, c, d, e, f, g), 1 pin for the decimal point (dp), and 2 pins for the common connection (either common cathode or common anode). The STM32 microcontroller has multiple GPIO pins that can be used to control the segments of the 7-segment LCD.

Step 3: Connect the Pins

The following is a general guide on how to connect the pins of the 7-segment LCD to the GPIO pins of the STM32 microcontroller:

Connect the common pin of the 7-segment LCD to either the ground (for common cathode) or the positive voltage (for common anode).
Connect the individual segment pins (a, b, c, d, e, f, g) and the decimal point pin (dp) to the GPIO pins of the STM32 microcontroller through resistors. The resistors are used to limit the current flowing through the segments and prevent them from burning out.
Connect the power supply pins of the STM32 microcontroller to the appropriate voltage source.

Here is a simple example of connecting a common cathode 7-segment LCD to an STM32F103C8T6 microcontroller:

Connect the common cathode pin of the 7-segment LCD to the ground.
Connect segment a to GPIO pin PA0 through a 330-ohm resistor.
Connect segment b to GPIO pin PA1 through a 330-ohm resistor.
Connect segment c to GPIO pin PA2 through a 330-ohm resistor.
Connect segment d to GPIO pin PA3 through a 330-ohm resistor.
Connect segment e to GPIO pin PA4 through a 330-ohm resistor.
Connect segment f to GPIO pin PA5 through a 330-ohm resistor.
Connect segment g to GPIO pin PA6 through a 330-ohm resistor.
Connect the decimal point pin dp to GPIO pin PA7 through a 330-ohm resistor.

Step 4: Write the Code

Once the hardware connection is complete, we need to write the code to control the 7-segment LCD using the STM32 microcontroller. The code should be able to set the appropriate GPIO pins to high or low to illuminate the desired segments and display the desired digits or letters.

Here is a simple example of code written in C using the STM32 HAL (Hardware Abstraction Layer) library to display the digit 0 on a common cathode 7-segment LCD:

#include "stm32f1xx_hal.h"

// Function to initialize the GPIO pins
void GPIO_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStruct = {0};

    // Enable the GPIOA clock
    __HAL_RCC_GPIOA_CLK_ENABLE();

    // Configure GPIO pins PA0 - PA7 as output pins
    GPIO_InitStruct.Pin = GPIO_PIN_0 | GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3 | GPIO_PIN_4 | GPIO_PIN_5 | GPIO_PIN_6 | GPIO_PIN_7;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
}

int main(void)
{
    HAL_Init();
    GPIO_Init();

    // Set the segments to display the digit 0
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_0, GPIO_PIN_SET); // Segment a
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, GPIO_PIN_SET); // Segment b
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_2, GPIO_PIN_SET); // Segment c
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_3, GPIO_PIN_SET); // Segment d
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET); // Segment e
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_SET); // Segment f
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_6, GPIO_PIN_RESET); // Segment g
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_7, GPIO_PIN_RESET); // Decimal point

    while (1)
    {
        // Main loop
    }
}

Troubleshooting Common Issues

Even with a proper connection and code, you may still encounter some issues when trying to connect the 7-segment LCD to the STM32 microcontroller. Here are some common issues and their solutions:

No Display

Check the power supply: Make sure the power supply to the 7-segment LCD and the STM32 microcontroller is stable and within the specified range.
Check the connections: Ensure that all the pins are properly connected and there are no loose connections or short circuits.
Check the code: Verify that the code is correct and the GPIO pins are being set to the appropriate levels.

Incorrect Display

Check the segment mapping: Make sure the segment mapping in the code matches the actual pin connections of the 7-segment LCD.
Check the resistor values: Ensure that the resistor values are correct and are limiting the current flowing through the segments properly.

Conclusion

Connecting a 7-segment LCD to an STM32 microcontroller is a relatively straightforward process that can be accomplished with a basic understanding of electronics and programming. By following the steps outlined in this blog, you should be able to successfully connect the two components and display the desired digits or letters on the 7-segment LCD.

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References

STM32F103C8T6 Datasheet
7-Segment LCD Datasheet
STM32 HAL Library Documentation