Saturday, August 12, 2017

Thermostat based on Arduino

This time we are going to build a Thermostat based on Arduino, temperature sensor and relay.
You can find on github

That gives you possibility to drive multiple devices in order to control temperature. In my case I have installed two fans on my attic in order to cool it down in summer. There are no windows, so I had to force airflow. First fan gets started when temperature reaches 30 degrees, second over 35.

You can control any reasonable amount of units, it's all configurable. You have also access to basic statistics:
Runtime of whole system

ON time for each relay

Statistics for 14 days

Statistics for 7th day


Whole configuration is stored in Config.h. You can change PINs controlling relays, reading temperature, thresholds or timings.


Configuring Relays

Let's assume that we would like to have 3 relays:

  • ID:0, PIN: 1, Temperature setpoint: 20
  • ID:1, PIN: 10, Temperature setpoint: 30
  • ID:2, PIN: 11, Temperature setpoint: 40
  • First you have to make sure that PIN of your choice is not already taken. All pins can be find in Config.h, they are defined by variables starting with DIG_PIN.

    You have to edit Config.h and configure PINs, thresholds and amount of relays. Obviously some properties already exists, so you have to just edit them.

    const static uint8_t DIG_PIN_RELAY_0 = 1;
    const static uint8_t DIG_PIN_RELAY_1 = 10;
    const static uint8_t DIG_PIN_RELAY_2 = 11;
    const static uint8_t RELAYS_AMOUNT = 3;
    const static int16_t RELAY_TEMP_SET_POINT_0 = 20;
    const static int16_t RELAY_TEMP_SET_POINT_1 = 30;
    const static int16_t RELAY_TEMP_SET_POINT_2 = 40;

    Now we have to setup relays and controller, this happens in RelayDriver.cpp

        initRelayHysteresisController(0, DIG_PIN_RELAY_0, RELAY_TEMP_SET_POINT_0);
        initRelayHysteresisController(1, DIG_PIN_RELAY_1, RELAY_TEMP_SET_POINT_1);
        initRelayHysteresisController(2, DIG_PIN_RELAY_2, RELAY_TEMP_SET_POINT_2);

    Choosing Controller

    There two controllers available Hysteresis and PID

    Hysteresis Controller

    It's the one chosen in example above, it has few additional configurations:

    const static uint32_t RELAY_DELAY_AFTER_SWITCH_MS = 300000; // 5 minutes
    const static uint32_t RHC_RELAY_MIN_SWITCH_MS = 3600000;

    RELAY_DELAY_AFTER_SWITCH_MS gives wait time for switching next relay. Imagine that configuration from our example would start working in 40 degrees environment. This would result in enabling of all three relays at the same time. This could eventually lead to high power consumption - depending on what you are controlling, electric engine for example consumes more power during start. In our case switching relays has following flow: first relay goes, wait 5 minutes, second goes on, wait 5 minutes, third goes on.

    RHC_RELAY_MIN_SWITCH_MS defines hysteresis, it's the minimum frequency for particular relay to change it's state. Once its on, it will remain on for alt least this period of time, ignoring temperature changes. This is quiet useful it you are controlling electric motors, since each switch has negative impact on live time.

    PID Controller

    This is advanced topic. Implementing such controller is simple task, finding right amplitude settings is a different story. 

    In order to use PID controller you have to change initRelayHysteresisController(.....) to initRelayPiDController(....) and you need to find right settings for it. As usual you will find them in Config.h 

    I've implemented simple simulator in Java, so that it's possible to visualize the results. It can be found in folder: pidsimulator.
    Below you can see simulations for two controllers PID a P. PID is not perfectly stable because I did not apply any sophisticated algorithm to find right values.

    On both plots required temperature is set to 30 (blue). Current temperature indicates read line. Relay has two states ON and OFF. When it's enabled temperature drops by 1.5, when it's disabled it rises by 0.5.

    Software Design

    Message Bus

    Different software modules have to communicate with each other, hopefully not both ways ;) 

    For example: 
    • statistics module has to know when particular relay goes on and off,
    • pressing a button has to change display content and it also has to suspend services that would consume many CPU cycles, for example temperature reading from sensor,
    • after some time temperature reading has to be renewed, 
    • and so on....
    Every module is connected to Message Bus and can register for particular events, and can produce any events.

    For example pressing Next button results in following flow:
    Some components have some tasks than needs to be executed periodically. We could call their corresponding methods from main loop, since we have Message Bus it's only necessary to propagate right event:


    Following libs are required to compile Thermostat:

    Wednesday, March 22, 2017

    Weather Station based on Arduino and NodeMCU

    We are about to build a weather station with forecast for three days, it will also include clock with local time and date.
    The whole project is based on Arduino, 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 few to build a display. In my case there are 3 lines, each consists of 8 modules, 24 it total, this give us 1532 single LEDs! 
    To drive 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 to use LED modules combined with MAX Chip, this will save you at least few hours, not mentioning time spent afterwards when single cable gets loose ;) Such combo-module has only 3 wires instead of 16.

    So we have 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 software. I've used separate line 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 that you can print sprites on it without bothering with transitions between LED modules. I did not find anything that would make me happy so I've decided to implement one by myself. It provides not only simple canvas, but fonts and few animations. Basically everything that will be needed to display time and weather.

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

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

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

    Putting things together


    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, so that you will not have to alter software.

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

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

    Next one is just another representation:
    Those last two schematics can be found here:

    Now it's time to build a software.

    Software for Arduino Mega

    You need to compile this project and upload into Arduino.
    In order to compile it, you will need to include SPI module and two other libraries: and

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

    You can use Sloeber for compilation, just follow those steps:
    1. Install Sloeber from
    2. Create new Arduino sketch and name it: LEDClock 
    3. Confirm next screens until it will ask you about code, select cpp
    4. Finish it, and you should get something like that:
    5. Clone LEDClock project from and move its content into Sloeber project folder. This operation should replace two files: LEDClock.h and LEDClock.cpp. Now we have Sloeber cpp project with right main files. Those wired steps were necessary, because I did not want to check in 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: and import into the project:
    8. Repeat this procedure for Logger:
    9. Imported project LEDDisplay has subfolder: examples. We have to exclude it from compilation, because it contains files with main-loop and this will disturb Sloeber. Select Properties on folder examples and check: Exclude resource from build:
    10. Now you should have following structure:
    11. You can upload it !

    Software for NodeMCU/ESP8266

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

    In order to provide weather and time to Arduino you will have to clone NodeMCUUtil, modify few scripts and finally upload those into NodeMCU. Below you will find exact instruction: 
    1. Compile firmware for NodeMCU so that it has all required modules. Here you will find instructions on it, and those are required modules: file, gpio, net, node, tmr, uart, wifi and cjson.
    2. Clone project containing Lua scripts:
    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 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 are using the only Serial Port in order 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