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• Inter-Integrated Circuit (I²C) is a common serial bus structure, which is used for attaching lower-speed peripheral ICs to processors and microcontrollers in a short-distance and intra-board communication.
• To know more about I²C, please click here.

Prerequisites

• Please click here if you are not sure how to use Ruff to write apps.
• Please click Driver- Getting Started) and Driver Model, if you know nothing about the driver development.

Using I²C

Please read the datasheet to confirm the interface is I²C.

Configuring driver.json

Please declare that your interface is I²C in driver.json. The declaration should be inputs with type as I²C.

{
    ...
    "inputs": {
        "i2c": {
            "type": "i2c",
            "args": {
                "address": -1
            }
        }
    }
}

Interface Properties

The following properties is accepted for I²C:

address - defines I²C address from the datasheet.

Writing a Driver

Reading Data

The driver could read data from there bus. For example, you will set a command as 0x01, and then read data in callback according to the datasheet:

function read(callback) {
    i2c.readBytes(0x01, function (error, value) {
        if (error) {
            callback(error);
            return;
        }

        callback(undefined, 0xff - value);
    });
}

Writing Data

The driver could write data to the bus. Here is an example that writes a byte to the bus:

var data = 0;
...

i2c.writeByte(-1, data);

For more information , please read I²C API document.

Application

Light Intensity Sensor (GY-30)

Light intensity sensor is a sensor that can measure luminance intensity. According to the datasheet, GY-30 needs an I²C interface whose address is 35. An I²C interface has been declared in driver.json, and the interface address is 35.

{
    "models": [
        "GY-30"
    ],
    "inputs": {
        "i2c": {
            "i2c": {
                "type": "i2c",
                "args": {
                    "address": 35
                }
            }
        }
    }
}

We provide the module with a method listed as follows:

• getIlluminance
  • Please write 0x20 to setup I²C interface.
  • Wait for a delay, then read two bytes from I²C interface to calculate illuminance.

'use strict';

var driver = require('ruff-driver');

module.exports = driver({
    attach: function (inputs, context) {
        this._i2c = inputs['i2c'];
    },

    exports: {
        getIlluminance: function(callback) {
            var i2c = this._i2c;

            i2c.writeByte(-1, 0x20, function(error) {
                if (error) {
                    callback(error);
                    return;
                }

                setTimeout(function() {
                    i2c.readBytes(-1, 2, function (error, values) {
                        if (error) {
                            callback(error);
                            return;
                        }
                        var value = Math.floor((values[0] << 8 | values[1]) / 1.2);
                        callback(undefined, value);
                    });
                }, 180);
            };
        }
    }
});