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A Simple Refrigerator Monitor

An Introduction To Squirrel Applications Example 2

In this example we will create an simple refrigerator monitoring application that takes synchronous readings from the temperature/humidity sensor and the internal light sensor. The light reading is used to determine if the refrigerator door is open or closed. The door status, temperature and humidity readings are sent to the cloud using the Initial State service. We will use a Hardware Abstraction Layer (HAL) to reference all hardware objects, and to organize our application code we will use a class. This code can be easily configured for use with an imp006 Breakout Kit, impExplorer Kit, impAccelerator Battery Powered Sensor Node or impC001 Breakout Board.

Skill level


This example will focus on writing Squirrel code. Please visit the Getting Started Guide on the Electric Imp Dev Center to learn how to configure your device with BlinkUp™ and how to use the Electric Imp IDE, impCentral™.

What You Learn

  • How to use Electric Imp libraries.
  • How to configure a sensor and take synchronous readings.
  • How to send data between device and agent.
  • How to send data to a cloud service such as Initial State.
  • How to use a Hardware Abstraction Layer (HAL).
  • How to write a class in Squirrel.

What You Need


// ---------------------------------------------------
// HAL's are tables that map human readable names to
// the hardware objects used in the application.

// Copy and Paste Your HAL here
ExplorerKit_001 <- {
    "LED_SPI" : hardware.spi257,
    "SENSOR_AND_GROVE_I2C" : hardware.i2c89,
    "ACCEL_I2C_ADDR" : 0x32,
    "PRESSURE_I2C_ADDR" : 0xB8,
    "POWER_GATE_AND_WAKE_PIN" : hardware.pin1,
    "AD_GROVE1_DATA1" : hardware.pin2,
    "AD_GROVE2_DATA1" : hardware.pin5
  • Assign your hardware class variables. In the Application class before the constructor you will find a number of class variables. You will need to re-assign the hardware variables so they look something like the example below. Do not copy and paste from this example, as these values may differ from the ones in your HAL.
// ---------------------------------------------------
// Application code, take readings from our sensors
// and send the data to the agent

class Application {

    // Time in seconds to wait between readings
    static READING_INTERVAL_SEC = 30;
    // Accelerometer data rate in Hz
    static ACCEL_DATARATE = 1;

    // Hardware variables
    i2c             = ExplorerKit_001.SENSOR_AND_GROVE_I2C;
    tempHumidAddr   = ExplorerKit_001.TEMP_HUMID_I2C_ADDR;
    pressureAddr    = ExplorerKit_001.PRESSURE_I2C_ADDR;
    accelAddr       = ExplorerKit_001.ACCEL_I2C_ADDR;

    // Sensor variables
    tempHumid = null;
    pressure = null;
    accel = null;

    constructor() {...}
  • Copy and paste the Agent Code into the Agent Code pane in the impCentral code editor.
  • Sign into Initial State.
  • Find your Streaming Access Key on the My Account page.
  • Navigate back to impCentral.
  • In the Agent code enter your Streaming Access Key into the Application class static variable STREAMING_ACCESS_KEY on line 23.
  • Hit the Build and Force Restart button to start the code.
  • Note the agent ID in the logs.
  • Navigate back to Initial State, find the Bucket that matches your agent ID.
  • Watch your data update in the Source, Lines, Waves and Tile views on the Initial State website.


Device Code

Agent Code