Raspberry pi GPIO helpers made for Deno

An interface for interacting and reading from the raspberry pi GPIO pins using sysfs.

Why?

Just for shits and giggles. Also why not? LOL!

Examples

Turning on an LED:

/*
- set pin direction to out. will queue up an instruction to auto-export the pin
- also sets the pin value to high. RPis do not have analogue: 1 for HIGH 0 for LOW
*/
import { executeInstructions, Pin, PinDirection, sleep } from "./mod.ts";

// full bash-level execution.
const led = new Pin(24, PinDirection.OUT, 1);
sleep(5);
led.setValue(0);
led.unexport();
executeInstructions(); // executes the above instructions.

it is highly recommended you unexport the pin after you are done using it.

It is also possible to take a more hybrid approach in which you come back to javascript:

// alternative hybrid (transfer from bash to JS and vice-versa)
// note that this approach is a bit slower and can cause timing issues with some 'dumb' sensors that require precise instruction sequences.
const led = new Pin(24, PinDirection.OUT, 1);
// the Pin constructor queues up some export instructions.. we are executing these here
executeInstructions(); // calls sysfs. returns a promise.

// standard JS timeout..
setTimeout(() => {
  led.setValue(0);
  led.unexport();
  executeInstructions();
}, 4000);

Listening for button press

import { executeInstructions, Pin, PinDirection } from "./mod.ts";

const button = new Pin(24, PinDirection.IN);
// the Pin constructor queues up some export instructions.. execute here.
await executeInstructions();
console.log("Waiting for button press");

while (true) {
  if (button.readValue() == 1) {
    console.log("button pressed");
    button.unexport();
    executeInstructions();
    break;
  }
}

Waiting for a pin to be a specific value

The following will issue an instruction to wait until the provided pin is set to HIGH (1) before continuing executing other commands:

const button = new Pin(24, PinDirection.IN);
button.waitForValue(); // wait (and thus blocking) occurs here
button.unexport();
await executeInstructions(); // this is where the main loop gets blocked in JavaScript.

Note that this blocking will happen in the sub-process created by Deno and will not block the JavaScript loop unless we use async await. it is also important to note that the blocking happens at the point of execution (i.e., when ‘await executeInstructions();’ is called)

Limitations

JavaScript it not very ‘precise’. i.e. no microsecond delay support for interacting with hardware that requires this (e.g. DHT11). To circumvent this, a method named pipeValue can be used to add read instructions in the instruction queue which will be executed along other instructions (including sleep instructions) in a shell.

Deno on the pi?

YES!!!! This will explain it all