obniz/parts/DistanceSensor/HC-SR04/index.js

obniz sdk for javascript

class HCSR04 {
  constructor() {
    this.keys = ['vcc', 'trigger', 'echo', 'gnd'];
    this.requiredKeys = ['vcc', 'trigger', 'echo'];

    this._unit = 'mm';
    this.reset_alltime = false;

    this.temp = 15;
  }

  static info() {
    return {
      name: 'HC-SR04',
    };
  }

  wired(obniz) {
    this.obniz = obniz;

    obniz.setVccGnd(null, this.params.gnd, '5v');

    this.vccIO = obniz.getIO(this.params.vcc);
    this.trigger = this.params.trigger;
    this.echo = this.params.echo;

    this.vccIO.drive('5v');
    this.vccIO.output(true);
    this.obniz.wait(100);
  }

  measure(callback) {
    let self = this;
    this.obniz.measure.echo({
      io_pulse: this.trigger,
      io_echo: this.echo,
      pulse: 'positive',
      pulse_width: 0.011,
      measure_edges: 3,
      timeout: (10 / 340) * 1000,
      callback: async edges => {
        if (this.reset_alltime) {
          this.vccIO.output(false);
          this.obniz.wait(100);
          this.vccIO.output(true);
          this.obniz.wait(100);
        }
        let distance = undefined;
        for (let i = 0; i < edges.length - 1; i++) {
          // HCSR04's output of io_echo is initially high when trigger is finshed
          if (edges[i].edge === true) {
            const time = (edges[i + 1].timing - edges[i].timing) / 1000; // (1/4000 * 8) + is needed??
            distance =
              (time / 2) * 20.055 * Math.sqrt(this.temp + 273.15) * 1000;
            if (self._unit === 'inch') {
              distance = distance * 0.0393701;
            }
          }
        }
        if (typeof callback === 'function') {
          callback(distance);
        }
      },
    });
  }

  async measureWait() {
    return new Promise(resolve => {
      this.measure(distance => {
        resolve(distance);
      });
    });
  }

  unit(unit) {
    if (unit === 'mm') {
      this._unit = 'mm';
    } else if (unit === 'inch') {
      this._unit = 'inch';
    } else {
      throw new Error('HCSR04: unknown unit ' + unit);
    }
  }
}

if (typeof module === 'object') {
  module.exports = HCSR04;
}