[−][src]Crate unflappable

Debounce a noisy digital input signal.

Even digital input signals can be noisy. The example usually cited is the flapping of physical contacts in a button or switch, but RF line noise can also cause digital input signals to bounce. Robust devices and embedded systems must debounce inputs.

This crate is a batteries-included embedded-hal InputPin debouncer, using the integration-based algorithm described by Kenneth A. Kuhn in a code sample on his website. You are highly recommended to read the code comments there.

Minimum supported Rust version

This crate makes use of trait bounds on a const fn, which is currently unstable. Therefore, we require use of the nightly compiler. When rust-lang/rust#67792 stabilizes, we will establish a MSRV policy.

Usage

You need to bring just a few things:

An InputPin, perhaps provided by a peripheral access crate (PAC) or hardware abstraction layer (HAL) for your chip.
An implementation of the Debounce trait, maybe just one from the default module.
Some way to regularly call the poll() method at about the right frequency (where "right" means "roughly consistent with the assumptions made in the Debounce trait implementation"). This may be an interrupt service routine (ISR), or it could just be a spin-delayed call from your main loop.
Storage for the debounce state. If you're using an ISR for polling, you'll want this to be a static.

Once you've worked out these details, the unflappable crate will take care of the rest.

[dependencies]
unflappable = "0.1"

Your implementation will consist of three major steps:

Create the debouncer.

If you're storing state in a static, that might be:

use unflappable::{debouncer_uninit, Debouncer, default::ActiveLow};
static DEBOUNCER: Debouncer<PinType, ActiveLow> = debouncer_uninit!();

Initialize the debouncer.

Next, initialize the Debouncer. You pass in the input pin and get back the debounced pin. If you're storing state in a static, that might look like this:

let debounced_pin = unsafe { DEBOUNCER.init(input_pin) }?;

See the docs on the init() method for safety details. Generally, if you haven't yet enabled interrupts you'll be fine.

Poll the debouncer.

On a regular basis, make a call to the poll() method of Debouncer, which might look like this:

unsafe {
    DEBOUNCER.poll()?;
}

Again, see the docs on the relevant method for safety information. The main idea here is that you should only ever poll() from one place in your code. We'd use a &mut reference, but, well, it's in static storage.

Debounced	A debounced pin.
Debouncer	A pin debouncer.
InitError	An error indicating that once-only initialization has been violated.

Enums

DeinitError	An error that arose during deinit.
PollError	An error that arose during polling.

Traits

Debounce

Static configuration of the debouncing algorithm.