Connecting Raspberry Pi 4 and STM32F407: Do You Need a Level Converter?

Explore whether you need a level converter for Raspberry Pi 4 and STM32F407 UART communication. This guide simplifies the complexities of GPIO voltage levels and ensures seamless communication.
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Connecting Raspberry Pi 4 and STM32F407: Do You Need a Level Converter?

Connecting a Raspberry Pi 4 with an STM32F407 Discovery board can unlock countless possibilities for projects in embedded systems and robotics. However, understanding how to connect these two devices, especially regarding voltage levels when using GPIO (UART) ports, can be a bit daunting. One common question is: Do you need a level converter for them to communicate effectively? Let’s break this down to find out!

Understanding the Voltage Levels

When dealing with microcontrollers and single-board computers, it's crucial to understand their voltage tolerance and output levels. In your case:

STM32F407 (STM32): While many STM32 pins can indeed handle 5V, they primarily operate at 3.3V. It is also important to note that the STM32 pins are typically referred to as "5V tolerant", meaning they can withstand voltages higher than their operating voltage without damage, but this doesn't necessarily mean they function optimally at those levels.

Raspberry Pi 4 (RPi): The general operating voltage for GPIO pins is 3.3V. Unlike the STM32, the RPi is not tolerant of higher voltage inputs (i.e., 5V could potentially damage the GPIO pins).

Do You Need a Level Converter?

The Short Answer: No!

In this specific case, you actually do not need a level converter to connect the STM32F407 to the Raspberry Pi 4 via UART. Here’s why:

Both devices operate at 3.3V. This means when you connect the UART pins (STM32 PD5 & PD6 to RPi Pin 8 (RX) & Pin 10 (TX)), you are effectively using compatible voltage levels. Thus, direct communication is possible without the need for a level shifter.

Important Points to Consider

Connection Method: When you connect the devices, ensure that the STM32 acts as the transmitting device, while the Raspberry Pi acts as the receiving device. This is a typical setup for UART communication.

Pin Configuration: Verify your pin connections before powering up your devices to avoid potential damage. Make sure to connect:

STM32 Pin PD5 (TX) to RPi Pin 10 (RX)

STM32 Pin PD6 (RX) to RPi Pin 8 (TX)

Investigating Pin Voltage Specifications

Although you might have come across conflicting information about some STM32 ports functioning at 5V, it’s crucial to refer to the official datasheets provided by STMicroelectronics. In those datasheets, you can find clear specifications on the voltage tolerance for each pin. Here are a few tips for your search:

Key Location: Look for the Electrical Characteristics section in your STM32 data sheet. This section should provide detailed information on voltage levels and tolerances for each individual pin.

Manufacturer Resources: Use resources like STMicroelectronics' official website and their application notes for further clarification on your device's specifications.

In Conclusion

For your project connecting a Raspberry Pi 4 with the STM32F407 over UART, you can directly connect the GPIO pins without any level converter! Just remember to check those datasheets for clarity on your hardware. “5V tolerant” might sound concerning, but in this case, it is perfectly safe to operate together at their native voltage levels of 3.3V. Happy tinkering!