26 lines
1.9 KiB
Markdown
26 lines
1.9 KiB
Markdown
---
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tags:
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- resource
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created: 2025-11-06 17:37
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---
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## Summary
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Notes on the use of the [rppal]() crate.
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## Notes
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### GPIO Pull Up/Pull Down Bias
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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.
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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.
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| When to Use | Typical Connection | |
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| -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------- |
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| **`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. |
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| **`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. |
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| **`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. |
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## References
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