1.9 KiB
1.9 KiB
tags, created
| tags | created | |
|---|---|---|
|
2025-11-06 17:37 |
Summary
Notes on the use of the rppal crate.
Notes
GPIO Pull Up/Pull Down Bias
The rppal::gpio::InputPin::set_bias method is used to configure the Raspberry Pi's built-in pull-up or pull-down resistors on an input pin.
You should use set_bias when interfacing with digital input sensors or switches that do not have their own external pull-up/pull-down resistors. These internal resistors ensure the input pin has a defined logic level (either high or low) when the external component is disconnected or floating, preventing erratic readings caused by electrical noise.
| When to Use | Typical Connection | |
|---|---|---|
Bias::PullUp |
When the input is connected to ground (GND) to signal a "low" state (e.g., a button connecting the pin to GND). The resistor pulls the pin voltage up to 3.3V by default. | One side of a button to the GPIO pin, the other side to GND. |
Bias::PullDown |
When the input is connected to 3.3V to signal a "high" state (e.g., a sensor outputting 3.3V). The resistor pulls the pin voltage down to GND by default. | One side of a button to the GPIO pin, the other side to 3.3V. |
Bias::Off |
When the external circuit already provides a defined logic level (e.g., an active sensor with a strong output signal, or an external pull-up/pull-down resistor is used). | Active sensor output connected directly to the GPIO pin. |