Aaron Ardiri
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Internet of Things (IoT)

RIoT Secure AB


I just couldn't do nothing with my new temperature sensor rig - I had to get it online!

In my previous blog entry I focused on rigging up some Dallas Semiconductor 1-Wire DS18B20 temperature sensors to an Arduino. In Australia; temperature is a big topic so; why not slap on a WiFi shield and have it communicate to a cloud service and then render the data into something useful so I can tease all my friends on how nice the weather is down here.

To get started; I needed to add some networking to the Arduino.

I chose to use the Arduino WiFi Shield as I could utilize my home WiFi network for data transmission. The great thing with Arduino shields is the ability to simply stack them on top of each other - I was able to put the existing prototyping shield on top of the WiFi shield as-is. The sketch will change slightly if you are using an Arduino Ethernet Shield - but the changes are minimal.

The first decision is where to send the data. I wrote a custom cloud service using php but you could use any public service for publishing the data from your sensors. dweet.io is a simple and free service if you are ok with publicly publishing your data for the whole world to see.

The source code for the sketch is available here:

In the interest of security I removed my WiFi network credentials and the URL of the web service where the data is sent. You will need to adapt the code to match the requirements of the service you want to connect to. In this example; I am using a HTTP POST without any authentication.

    // network configuration
    char ssid[] = "XXXXXXXX";               // your network SSID (name)
    char pass[] = "XXXXXXXX";               // your network password
    int status = WL_IDLE_STATUS;
    // server configuration
    char server[] = "XXX.XXX.XXX.XXX";      // IP address of server
    char serverName[] = "www.xxxxxxxx.com"; // hostname of server
    char serverUrl[] = "/xxx/";             // URL on the server for POST
    int  port = 80; 

The above settings are the ones to change to match your WiFi network and the server you wish to connect to. The contents of the postdata variable will also need to match the requirements of the service you will connect to. The Arduino Playground has some example sketches showing how to perform a HTTP GET and POST request - in fact; my code was based on them.

The first modification to the sketch was to average out the four temperature sensors to use as a reading.

    float temp_accumulative;
    int   temp_count;
    // we want to start counting temperatures
    temp_accumulative = 0;
    temp_count        = 0;
    // do we have no more addresses?
    if (!onewire.search(addr))
      Serial.println("No more addresses.");
      // lets figure out the average temperature across the sensors
      celsius = temp_accumulative / temp_count;
      fahrenheit = celsius * 1.8 + 32.0;
      // display the resulting average temperature
      Serial.print("  Temperature (average) = ");
      Serial.print(" Celsius, ");
      Serial.println(" Fahrenheit");
    // record the value for the average calculation
    temp_accumulative += celsius;

Easy enough - surely that doesn't require any explanation!

The next part was to create the variables that I would send over to my web server. In my case I built a generic web service that accepts a unique identifier (uuid) and data in the form of a JSON message - this lets me use my service for more than just tracking the temperature. The basic essence is that the Arduino would send the following variables:

    uuid = 73c374f6-75d4-40ab-af37-412c575c18be
    data = { temperature: 20.0 } 

This is stored in the postdata variable - using URL Encoding - this makes sure nothing is lost or mis-interpreted in the server side when the data is received. There is a catch to getting your temperature into a string - as Arduino doesn't support %f in the sprintf function.

    char str_celsius[8];
    char postdata[128];
    // build some jason for the cloud service
    dtostrf(celsius, 4, 2, str_celsius);
    sprintf(postdata, "uuid=73c374f6-75d4-40ab-af37-412c575c18be&" \
                      "data=%%7B%%22temperature%%22%%3A%s%%7D", str_celsius);

The next step is to make a connection and send the data over the network:

    if (client.connect(server, port))
      client.println("POST /");
      client.println(" HTTP/1.1");
      client.print("Host: ");
      client.println("User-Agent: Arduino/1.0");
      client.println("Connection: close");
      client.println("Content-type: application/x-www-form-urlencoded");
      client.print("Content-Length: ");

You do not need all of the parameters; but, it helps to identify that the User-Agent is an Arduino and that you are defining the Content-type to specify the content is a HTTP POST with URL encoding. The content of the postdata variable is provided and we set the Content-Length parameter appropriately. If you are interested in the full HTTP/1.1 protocol - you can read up it within RFC2616.

The sketch also has some other cool goodies to handle reconnecting to a WiFi network, being able to receive the response and auto-close the connection if no data has been received within a specific period of time. There is also a millisecond counter to send data roughly once a minute (should be enough).

Running the sketch provided the following on the Console Log window: (server details removed)

    OneWire Sketch
    author:  Aaron Ardiri
    version: Nov 18 2015
    Attempting to connect to WiFi SSID: xxxx
      IP Address:
      Subnet Mask:
      MAC address: 78:C4:0E:03:A9:E2
    ROM = 28 F0 74 DC 06 00 00 DC
      Chip = DS18B20
      Data = 9D 01 4B 46 7F FF 03 10 57  CRC=57
      Temperature = 25.81 Celsius, 78.46 Fahrenheit
    ROM = 28 E1 CF DC 06 00 00 8F
      Chip = DS18B20
      Data = A1 01 4B 46 7F FF 0F 10 D9  CRC=D9
      Temperature = 26.06 Celsius, 78.91 Fahrenheit
    ROM = 28 99 F3 DD 06 00 00 9C
      Chip = DS18B20
      Data = 95 01 4B 46 7F FF 0B 10 0B  CRC=B
      Temperature = 25.31 Celsius, 77.56 Fahrenheit
    ROM = 28 05 89 DE 06 00 00 08
      Chip = DS18B20
      Data = A0 01 4B 46 7F FF 10 10 6E  CRC=6E
      Temperature = 26.00 Celsius, 78.80 Fahrenheit
    No more addresses.
      Temperature (average) = 25.80 Celsius, 78.43 Fahrenheit
    Attempting connection to server...
    :: successfully connected to server
    -- request:
    POST /xxx/ HTTP/1.1
    Host: xxx.xxxxxxxxx.xxx
    User-Agent: Arduino/1.0
    Connection: close
    Content-type: application/x-www-form-urlencoded
    Content-Length: 78
    -- response:
    HTTP/1.1 200 OK
    Date: Wed, 18 Nov 2015 06:08:13 GMT
    Server: Apache/2.4.10 (Debian)
    Vary: Accept-Encoding
    Content-Length: 105
    Connection: close
    Content-Type: text/html; charset=UTF-8
    uuid = 73c374f6-75d4-40ab-af37-412c575c18be
    _ts_ = 2015-11-17 23:08:13
    data = {
        "temperature": 25.8
    :: done

The device has been connected for almost twenty four hours now and I also put together a quick graph of the temperature which you can see below. The minimum temperature on my alfresco in the last twenty four hours was 16.72C at 01:39 in the morning - and the temperature peaked at 15:47 with a whopping 21.34C. It was a mild spring day here in the south-west of Western Australia.

I may just need to make a small cover for the unit but effectively I could leave the device running over the summer and see how warm it gets - it can easily reach 35C in the shade here in the summer time. Best of all, I can now monitor the temperature on my alfresco from anywhere in the world!


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Arduino WiFiShield101 - available, but is it ready?
Hands-on with Dallas Semiconductor 1-Wire and Arduino

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