Fullscreen HTML5Med Res (??MB)HTML4

Logging data to the ’net using Arduino This circuit and software show how you can easily log data to the cloud from a remote location, using an ESP8266-based Arduino module. By Bera Somnath ThingSpeak.com is a website supporting open source software on the “Internet of Things”. It’s basically a repository for remotely logged data that you can access to download your sensor data at any time. This circuit and software show how you can log data to it at a remote location easily, using an ESP8266-based Arduino-type module and retrieve it over the internet later. The ESP8266 is a chip which combines a powerful ARM processor with a WiFi transceiver and antenna. We’re using a WeMos D1 R2 which is compatible with the Arduino IDE but instead of an Atmel ATmega processor, it uses the ESP8266. It’s a low-cost device that’s readily available and contains everything you need to communicate over WiFi. The parts required for this sample project can be acquired for under $20 and the result is a battery-powered device which measures its local temperature and humidity and then uploads them periodically to ThingSpeak.com You can view the logged results at any time using your PC. Setting up an account Before using ThingSpeak you need to sign up for an account and “open a channel” for your logging device. To do this, you need a working email address. Once registered, you can create as many channels as you need. Simply go to https://ThingSpeak.com and follow the instructions to register and set up a channel. Each channel has a channel ID, a “write” API key and a “read” API key. Note these down as we will need them later. Each channel can contain up to eight streams of data. You can then assign names to these streams. Our example 92  Silicon Chip will log temperature and humidity from a DHT-22 sensor, so name the first two “temperature” and “humidity”. Configuring the WeMos board Fig.1 shows how we connect the DHT22 sensor to the WeMos board, along with a lithium rechargeable battery to power it and a small OLED display so we can see the current status. If you were to position one or more of these modules remotely, having gotten them working, you wouldn’t need to connect the display. Communication with the DHT22 is over a single-wire bus and this data pin is connected to digital I/O pin D5 of the WeMos module. The OLED display is driven via an I2C serial bus and this is wired to the hardware SCL (clock) and SDA (data) pins, D1 and D2, of the WeMos board. Both modules run off the same 3.3V supply as the WeMos module. Not only does the WeMos ESP8266 board have onboard WiFi, saving you the hassle of connecting a shield for this task, as noted earlier, its processor is faster and it also has more memory. We got ours from AliExpress for less than $5. Having installed the latest version of the Arduino IDE on your computer (if you didn’t have it already), you will need to enable support for ESP8266based boards. Open up preferences in the IDE and under “Arduino Board Manager URLs”, enter: http://arduino.esp8266.com/stable/ package_esp8266com_index.json Hit OK, then go to Tools → Boards → Board Manager, type in “esp8266” in the search box, click on the entry which appears below and then click on the “Install” button. This will result in around 160MB of compilers and associated files being downloaded and installed on your computer. You can now go to the Tools → Board menu and select the “WeMos D1 R2 & mini” entry from the drop-down list. You will then need to install three The data logger was built using a small breadboard for the extra parts with the Li-ion battery sitting underneath the WeMos board. Otherwise, most connections were made using flying leads. siliconchip.com.au Arduino libraries: DHT, OneWire and thingspeak-arduino. All three are supplied in the download package from the Silicon Chip website, which also includes the sketch itself. Then install these libraries using the Sketch → Include Library → Add .ZIP Library option, if you didn’t have them already. You will then need to open up the sketch and modify it so that it can connect to your WiFi network and your ThingSpeak channel. Change the ssid[] and pass[] strings to suit your WiFi network and the myChannelNumber and myWriteAPIKey strings to match those you noted earlier when setting up your ThingSpeak account. You can then compile/verify the sketch and it’s ready to be uploaded to the WeMos board. Having wired up the circuit as shown, with the battery disconnected, plug the WeMos board into your PC via USB, ensure the Arduino IDE is configured to use the correct port and then upload the sketch. It should spring into life straight away. Once working, you can add more sensors later, which can be logged to the six spare streams in your channel. The software The code is broadly divided into a few parts. The first few lines include the relevant headers, then create instances of the WiFi, DHT, OLED and ThingSpeak.com objects. The setup function initialises these objects by calling the begin() method then inside the main loop, it retrieves the temperature and humidity from the sensor and then transfers the data to ThingSpeak. com at thirty-second intervals. The entire code is less than 70 lines, including the comments. If you eliminate the OLED-related lines, fewer than 30 remain. If you look at the code, you will see the following lines: ThingSpeak.writeField( myChannelNumber, 1, h, myWriteAPIKey); delay(15000); // ThingSpeak will only accept updates every 15 seconds. ThingSpeak.writeField( myChannelNumber, 2, t, myWriteAPIKey); delay(15000); // ThingSpeak will only accept updates every 15 seconds. Fig.1: block diagram showing the connections required to and from the WeMos module. The OLED module isn’t required for it to run, and is used more as a convenience during set-up and debugging. tion calls add a pause of fifteen seconds between each transmission. Once you declare a channel “public”, it will have a URL which is accessible to all. Just by clicking that URL, anybody can view the channel. Otherwise, for a private channel, you have to log on to see that channel’s output. Power Consumption While active, the unit draws around 80mA but most of this is the WiFi chipset. To reduce overall power con- sumption, the WiFi interface is put to sleep when not needed, reducing idle power consumption to 22mA, giving an average of around 30mA. If the optional OLED display is used, that adds another 40mA. Without the OLED display, the device can run for hours on a small LiFePO4 cell. We recommend you use this type of rechargeable cell since its normal voltage range is close to the 3.3V that SC the WeMos board requires. An example shot showing what kind of data you can expect to see when the software is up and running. These are responsible for uploading the sensor data to your ThingSpeak. com channel. The intervening funcsiliconchip.com.au September 2017  93