Wednesday, March 22, 2017

Weather Station based on Arduino and NodeMCU

We are about to build a weather station with a forecast for three days, including a clock with local time and date.
The whole project is based on Arduino, and NodeMCU provides access to the Internet over WiFi. The display is built from single LEDs. Since they can be really bright, it adopts illumination based on light conditions.


Let's start from the beginning ;)
I've found those 8x8 LED modules:

So I've decided to combine a few to build a display. In my case, there are 3 lines, each consisting of 8 modules, 24 in total, this gives us 1532 single LEDs! 
To drive a single module, I've chosen MAX72xx, I also wanted to improve my soldering skills, so I've decided to go for 24 PIN DIP chips and solder them to prototype boards:

Well, that worked out pretty well when it comes to those skills, but I would recommend using LED modules combined with MAX Chip, this will save you at least a few hours, not to mention time spent afterward when a single cable gets loose ;) Such a combo module has only 3 wires instead of 16.

So we have a hardware part for our display: 24 led modules with drivers. Now it's time to light them up! I've decided to go for Arduino Mega because it has two serial ports, so it's easier to debug things (one port will be used for communication with EPS8266). You could also use Uno, in this case, you would have to daisy chain MAX chips and change addressing in the software. I've used separate lines for each Max chip, but Uno just does not have enough digital output pins.

I was looking for API that will join all led modules into one canvas, so you can print sprites without bothering with transitions between LED modules. I did not find anything that would make me happy, so I implemented one myself. It provides not only a simple canvas but fonts and a few animations. Basically, everything that will be needed to display time and weather.

So ... we have a display and API to control it. Now we need to get the date and weather. Arduino does not support Internet connectivity and does not have enough resources to process incoming data. So I've decided to use NodeMCU. With a few Lua scripts, I could implement a simple API accessible over the serial port. Arduino connects over it with NodeMCU, obtains time, date, and weather, and displays it.

To provide the date, NodeMCU connects with the NTP server and receives UTC time, afterwards it calculates the local date from it. I could use one of the Internet services to grab the date, but I was looking for a solution that would remain stable for a long time. Those services can change their API or just go offline, but the NTP protocol will remain unchanged. In the worst case, you will have to change the server name. The current implementation also supports failover through many different servers, so you will probably not have to bother with it soon ;)

Getting the weather was a bit tricky because I had to find an API that would return a response small enough so it could be parsed by NodeMCU. I've decided to use Yahoo Weather. They provide a nice REST API with a small and simple response. Hopefully, they will keep interfaces stable for a long time.....


Putting things together

Hardware

First, you have to build the display, I've already described it in this post: Arduino LED Display . You can use the same pin numbers on Mega to not have to alter the software.

After the display is ready, you should connect ESP8266 and the photoresistor. The Schematic below contains all hardware elements together:

The area on the top right corner is the display itself - 8x3 LED modules. Every single module exposes 3 PINs, those are MAX 72xxx PINs responsible for communication over SPI.
Here you will find an exact schematic of the single module, including SPI PINs:


The next one is just another representation:
Those last two schematics can be found here: https://github.com/maciejmiklas/LEDDisplay/tree/master/doc/fritzing

Now it's time to build software.

Software for Arduino Mega

You need to compile this project https://github.com/maciejmiklas/LEDClock and upload into Arduino.
In order to compile it, you will need to include SPI module and two other libraries: https://github.com/maciejmiklas/LEDDisplay and https://github.com/maciejmiklas/LEDDisplay

Here is a compiled software for those with the same hardware setup.

You can use Sloeber for compilation, just follow the steps:
  1. Install Sloeber from http://eclipse.baeyens.it
  2. Create a new Arduino sketch and name it: LEDClock 
  3. Confirm the next screens until it asks you about code, select cpp
  4. Finish it, and you should get something like that:
  5. Clone the LEDClock project from https://github.com/maciejmiklas/LEDDisplay and move its content into the Sloeber project folder. This operation should replace two files: LEDClock.h and LEDClock.cpp. Now we have the Sloeber cpp project with the right main files. Those wired steps were necessary because I did not want to check into GitHub IDE-specific files. This is our structure now:
  6. There are still compilation errors, we will now add missing libraries
  7. Clone LED Display API: https://github.com/maciejmiklas/LEDDisplay and import into the project:
  8. Repeat this procedure for Logger: https://github.com/maciejmiklas/ArdLog
  9. Imported project LEDDisplay has a subfolder: examples. We must exclude it from compilation because it contains files with the main-loop, which will disturb Sloeber. Select Properties on folder examples and check: Exclude resource from the build:
  10. Now you should have the following structure:
  11. You can upload it!

Software for NodeMCU/ESP8266

I am using EPS8266 with a Lua interpreter, this combination is called NodeMCU.

To provide weather and time to Arduino, you must clone NodeMCUUtil, modify a few scripts and finally upload those into NodeMCU. Below you will find exact instructions: 
  1. Compile firmware for NodeMCU so that it has all required modules. Here you will find instructions on it, which are the required modules: file, gpio, net, node, tmr, uart, wifi and cjson.
  2. Clone project containing Lua scripts: https://github.com/maciejmiklas/NodeMCUUtils
  3. Edit serialAPIClock.lua and set UTC offset for your location. This will be required to calculate local date from UTC time. For most European countries it's already set to correct value. For US you will have to replace require "dateformatEurope" with require "dateformatAmerica" and rename all method calls from setEuropeTime to setAmericaTime
  4. Edit yahooWeather.lua and provide city and country that you would like to have weather for.
  5. Create a new file called: credentials.lua and specify login data for WiFi connection, it's just one line, for example cred = {ssid = 'openwifi', password = '123456789'}
  6. Upload all Lua scirpts from main project's folder into NodeMCU:
    • credentials.lua
    • dateformat.lua
    • dateformatAmerica.lua
    • dateformatEurope.lua
    • ntp.lua
    • ntpClock.lua
    • serialAPI.lua
    • serialAPIClock.lua
    • serialAPIYahooWeather.lua
    • wlan.lua
    • yahooWeather.lua
  7. Now for the final touch, we need the init-file that will be executed right after NodeMCU boots up. In our case, we use only the Serial Port to expose weather and clock API. This also means that once our API is registered, it's impossible to execute standard NodeMCU commands, like file upload. For this reason init-script has two seconds delay, during this time you can still upload files, or just remove current init.lua file. Init-files are there: NodeMCUUtils/init/serialInit
    • init.lua
    • serialInit.lua

Github repos used in this project