Mikrocontroller am Beispiel Arduino - oder Der twitternde Farn

Introduction

• We are using an ESP8266 Microcontroller named WeMos D1. It comes in two revisions.

(Pictured: new revision R2 on top and old revision below)

Installation

• Download Arduino IDE from https://www.arduino.cc/en/main/software
• Unpack and run
• Make the Arduino IDE familiar with your microcontroller:
  • Go to File -> Preferences and add the URL http://arduino.esp8266.com/stable/package_esp8266com_index.json under "Additional Board Manager URLs"
  • open Tools -> Board: ... -> Board Manager
  • search for "ESP8266" and select the matching driver below
  • click install
  • open Tools -> Board: ... and select "WeMos D1(Retired)" or "WeMos D1 R2 & mini" according to the name printed on your board
• USB setup:
  • Connect your Arduino board to the USB port of your computer and choose Tools -> Port -> /dev/ttyUSB0.
  • On Linux: sudo chmod o+rw /dev/ttyUSB0 to enable read/write to that port as a normal user. You have to do this each time you disconnect and reconnect the microcontroller.

First example: Switch off a LED on the board

The IDE shows two functions. setup() is run once at the beginning (used for assigning start values to variables etc.). loop() is run repeatedly.

• See example01/example01.ino.

• Click on the small check mark ("verify") on top to compile the code. When it's done (and there are no errors) it will show "Done compiling."

• Upload the compiled code to the board using the arrow button (2nd from left). If it works, you should see

    Uploading 227200 bytes from /tmp/build097a90998118e101b31481be08ada238.tmp/example01.ino.bin to flash at 0x00000000
    ................................................................................ [ 36% ]
    ................................................................................ [ 72% ]
    ..............................................................                   [ 100% ]
  

The LED labelled SCK goes off.

You can now control the brightness of your LED with the MEIN_LED value.

Second example: Make the LED blink

• See example02/example02.ino.

  • Verify and upload the code.
  • The LED will blink.

• Bonus: example02a/example02a.ino. The LED changes brightness each 500 ms and goes off for 1 second.

Third Example: Control the LED with a light sensor

(You need a board with a light sensor to run this, e.g. Arduino Mega ADK. Make sure you pick the right board on Tools -> Board: ...)

• See example03/example03.ino.
  • This program turns on the LED on the board when it's dark, and off when it's bright.
• Click the Serial Monitor icon on the upper right corner of the IDE to see the output of the serial console of your Arduino.

Fourth example: Humidity sensor setup

• See example04/example04.ino.
• Assemble the humidity sensor.
• Disconnect the microcontroller from the computer (!).
• Connect the humidity sensor curcuit board to the microcontroller
  • VCC --> 3.3V
  • GND --> GND
  • AO (analog output) --> AO

• Connect the controller to the computer again and put the sensor into the flower pot.

• You can now watch the humidity values of the flower pot and other things.
  • The values range from 0 to ~1000.
  • High values mean it's dry, low values mean it's humid.

Fifth example: Control the LED with the humidity sensor

• See example05/example05.ino.
• The LED should blink for 5 seconds when it's too dry.

Sixth example: Add measuring interval for humidity sensor

• When you measure, there's electric current going through the sensor permanently. This decreases the lifetime of the sensor.
• Our idea: Measure only once in a certain interval.
• How do we achieve this? We measure only once every 1/5 second and switch off the sensor in between (when it's not needed).
  • Disconnect the Arduino from the computer.
  • Take the wire connected to 3.3V on the microcontroller and connect it to D8 (old rev) or D3 (new rev).
  • Reconnect the Arduino to the computer.
• See example06/example06.ino.

Seventh example: WiFi setup and web server

• See example07/example07.ino.

  • Connect Arduino to a WiFi

  • Arduino should output its IP address to the serial console:

      I'm Arduino, trying to connect to the Wifi blubb blubb blubb blubb blubb \
      blubb blubb blubb blubb blubb blubb blubb blubb blubb blubb blubb blubb \
      blubb blubb blubb blubb blubb blubb successfully connected!
      10.42.0.130
    

  • Ping Arduino from your computer to test connectivity

      $ ping 10.42.0.130
      PING 10.42.0.130 (10.42.0.130) 56(84) bytes of data.
      64 bytes from 10.42.0.130: icmp_seq=1 ttl=128 time=23.8 ms
      64 bytes from 10.42.0.130: icmp_seq=2 ttl=128 time=16.5 ms
      64 bytes from 10.42.0.130: icmp_seq=3 ttl=128 time=11.8 ms
    

  • Start a web server on Arduino

Using a command line/shell, try to access the Arduino web server at the given URL

$ curl 10.42.0.130
Guckuck!

The serial console of the Arduino IDE will display

GET / HTTP/1.1
Host: 10.42.0.130
User-Agent: curl/7.50.1
Accept: */*

Our web server is working!

Eighth example: Website with two buttons light switch

• We now want a website with two buttons: Lights on / Lights off.
  • Make a HTML form with method="GET".
  • Register the following URLs:
    • / ... show form
    • /?LightsOn=on ... show form, turn on light
    • /?LightsOff=off ... show form, turn off light
• See example08/example08.ino.

Ninth example: Website with light switch and humidity value

• Display the humidity value below the buttons.
• See example09/example09.ino.

Tenth example: IFTTT and Twitter

• The source code is at example10/example10.ino.
• Register an account at IFTTT maker.
• How to trigger events: Remember the URL ("Make a POST or GET web request to:"). Your Arduino has to call this URL to make a Tweet. It needs to be added to the source code. Make sure to replace "https" with "http", as Arduino doesn't support SSL encryption out-of-the-box.
• Go to https://ifttt.com/twitter and click "Connect". Connect your Twitter account.
• Then click "Create a new recipe". We now need to set an if-condition or trigger. Click the word "this" and type in "Maker".
• "Receive a web request" will appear. Enter an event name such as "Water the plants" or similar. Then click the "Create trigger" button.
• The if-condition is now set. IFTTT will trigger an action every time it receives a HTTP request from the Arduino. Now let's define that action - tell IFTTT to Tweet for us.
• The then-condition has to be linked to Twitter. Click "that", type in "Twitter" and pick "Post a Tweet".
• Enter a Tweet message you like. We can add values of parameters, so we know what's going on with the humidity sensor. Values can be specified with two curly braces like "{{Value1}}" (capitalised V is important here).
  • Note that in the Arduino source code, the current humidity value gets appended to the URL as a parameter (like ?value1=). This value is going to be displayed in the Tweet.
• Then click "Create action" and "Create recipe".
• Done!