Modern microcontrollers, such as the ESP32 and Raspberry Pi, operate at 3.3V logic levels, while many sensors and modules, like the Arduino Uno, use 5V logic. Directly connecting a 5V signal to a 3.3V microcontroller can damage the input pins. To safely interface 5V and 3.3V devices, we need a voltage level conversion method. In this article, we will explore two popular techniques: a simple resistor voltage divider (1kΩ + 2kΩ) and a bidirectional logic level shifter.
Method 1: Using a Voltage Divider (1kΩ + 2kΩ)
A voltage divider is the simplest way to step down a 5V digital signal to 3.3V using two resistors. The formula for calculating the output voltage is:
Vout=Vin×R2R1+R2V_{out} = V_{in} \times \frac{R_2}{R_1 + R_2}
For a 1kΩ (R1) and 2kΩ (R2) resistor setup: Vout=5V×2kΩ1kΩ+2kΩV_{out} = 5V \times \frac{2kΩ}{1kΩ + 2kΩ} Vout=5V×23V_{out} = 5V \times \frac{2}{3} Vout=3.33VV_{out} = 3.33V
Connections for Voltage Divider
- Connect the 5V signal to one end of the 1kΩ resistor (R1).
- Connect the other end of R1 to one end of the 2kΩ resistor (R2).
- Connect the junction between R1 and R2 to the 3.3V logic input pin (e.g., ESP32 GPIO).
- Connect the other end of R2 to GND.
Advantages of Voltage Divider
✔️ Simple and inexpensive (only two resistors required).
✔️ Works well for one-way (unidirectional) signals like UART TX.
✔️ Suitable for applications where speed is not critical.
Disadvantages of Voltage Divider
❌ Not reliable for high-speed signals (e.g., SPI, I2C, fast PWM).
❌ Unidirectional only (does not work for bidirectional communication like I2C).
❌ Resistor values must be chosen carefully to avoid excessive loading.
Method 2: Using a Bidirectional Logic Level Shifter
For bidirectional communication (e.g., I2C, SPI), a logic level shifter module is a better choice. These modules use MOSFETs and pull-up resistors to safely convert signals between 5V and 3.3V in both directions.
How a Logic Level Shifter Works
- The module has two sides:
- High Voltage (HV) side (connects to 5V logic devices).
- Low Voltage (LV) side (connects to 3.3V microcontrollers).
- The MOSFET-based circuit automatically shifts signals up or down depending on the direction of communication.
- Works with I2C, SPI, UART, and GPIOs without affecting signal integrity.
Connections for Bidirectional Logic Level Shifter
- Connect the HV (High Voltage) pin to 5V.
- Connect the LV (Low Voltage) pin to 3.3V.
- Connect GND to both 5V and 3.3V circuits.
- For each signal line:
- Connect the 5V device TX/SCL/SCK pin to the HVx pin on the module.
- Connect the 3.3V device RX/SDA/MISO pin to the LVx pin on the module.
Advantages of Logic Level Shifter
✔️ Bidirectional support (perfect for I2C, SPI, UART).
✔️ Preserves signal integrity for high-speed communication.
✔️ Plug-and-play solution for complex circuits.
Disadvantages of Logic Level Shifter
❌ Slightly more expensive than resistors.
❌ Requires an additional module, increasing circuit complexity.
Which Method Should You Use?
| Feature | Voltage Divider | Logic Level Shifter |
|---|---|---|
| Cost | Low (2 resistors) | Medium (IC or module) |
| Speed | Low | High (works with fast signals) |
| Direction | Unidirectional | Bidirectional |
| Best for | Simple signals (UART TX, GPIOs) | I2C, SPI, bidirectional UART |
Conclusion
If you’re working with simple, unidirectional signals, a voltage divider (1kΩ + 2kΩ) is a quick and cheap solution. However, for fast and bidirectional signals, a logic level shifter is the better choice. Understanding these two methods ensures safe and reliable communication between 5V and 3.3V devices in your projects!
Have questions or suggestions? Let us know in the comments below!