Project "SmartHome" build: Central

My personal project to build Smart Home system and learn Micropython by utilising LVGL on ILI9341 display by using ESP32 microcontroller.

Initial idea was to have one SmartHome Central space where I could see all rooms temperature and humidity measures in one place. I'm also planning to add soil moisture sensor (built on my favourite ESP32) and later on- control some of appliances at home. I did not want to go with already built systems (HomeAssistant or Tasmota) as my goal was to learn to build multi-component system by myself.

Central Unit

Source is available on my github repository. Comments and ideas are welcome.

Central unit is ESP32 generic (no PSRAM) with 4mb PSRAM microcontroller with Micropython + LVGL firmware and ILI9341 display. It listenf for messages in MQTT and display innformation on screen. Also weather integration is made: current weather outside and forecast

Wire connection diagram
ESP32 ILI9341
3v3 VCC
26 CS
33 Reset
27 DC
23 SDI (Mosi)
18 SCK
32 LED
19 SDO (Miso)
14 T_CLK
15 T_CS
13 T_DIN
12 T_DO
35 (not used) T_IRQ

I've used two different SPI busses, One for ILI9341 and another one for XTP2046 (touch) as i had plenty of pins on my central device.

Proxy unit

Source is available on my github repository.

Proxy unit is also ESP32 generic based device, witch listens to all available BLE advertisement packages. It filters know MAC addresses and forward that messages to MQTT.

BLE thermometers

Probably, this section may be most interesting for various DIY'ers :-)

Once I've stumbled on Youtube video, where person was discussing to DIY or BUY temperature sensor. Probably, you can not DIY cheaper yourself, because this sensor cost 4$. Yes, four dollars! It can be used as stand alone device as it is has its own screen.

Issue was BLE advertisement is encoded. Dear Xiaomi- let us use your devices freely in out projects. Open source is future!

But lucky for us, DIY'ers, AAron Christophel dedicated a lot of his own time and was able to write custom firmware for extra cheap (4$) Xiaomi Thermometer model LYWSD03MMC. Its easy to change firmware in thermometer with any regular Android device. No additional hardware is needed. To change firmware- download bin file from ATC github repository to your phone. Then open web flasher. I've used Android Chrome browser for flashing.

Always consult official repository how flashing procedure is done! It may change over time.

  1. Download firmware file
  2. Enable bluetooth on your device.
  3. Open web flasher page and press button “Connect” and choose your device. If it is the first time you flash firmware- its name will be LYWSD03 or something similar. After flashing- it will be ATC_######. Last six digit will be last six pairs of your device mac address.
  4. Do activation”. It connect to device and calculates Device ID, token and Bind key. Nothing will be changed in firmware.
  5. Choose bin file. Take care of what file you choose. Mistake can brick your device. Anyway, not a huge loss- it's dirt cheap :-)
  6. Start flashing”. It may take 60-100 seconds to complete. It should restart after finishing. If it did not- wait 5 minutes and remove battery from thermometer.

Soil moisture sensors

I'm planning battery (LiFePO4) powered ESP32 device to measure soil moisture of my balcony greens and send data to central unit via BLE advertisement. My choice of LiFePO4 battery was because it's perfect candidate to directly power ESP32 (without any power management devices). More about that in my later posts. Now i'm in progress of building this.

What i have learned

  • How BLE advertisement works;
  • Setup environment, required for Micropython firmware building;
  • What is MQTT and how it works, setup server locally.

Pure python and very simple event management library

In event driven programming events are crucial. My requirements was Micropython platform on ESP32 micro-controller, so i could not use any other events library out-there. I've stumbled one very basic, very simple library and gave it a try… and it worked out-of-the-box for my case. When testing various event management libs out there I've stumbled on something similar, but it did not worked within classes. Python is nothing but classes everywhere :)

I was testing and extended this very simple python script, that perfectly works as main element in event driven development.

Strengths of library:

  • Observer can be declared before event type is created
  • Events can be fired even if there is no observers.
  • Works as pure python script
  • Works on micropython platform
  • Event name can be any string

I'm using this solution for event for timer, that fires each second and observe “ticker” where i need to update clock. I use clock in multiple places in my micropython script and i can get away with just one hardware timer used.

Honorable mentions goes to Pithikos from StackOverflow this answer

I have extended this library with possibility to forget event.
class Observer():
    _observers = []
    def __init__(self):
        self._observed_events = []
    def observe(self, event_name, callback_fn):
        self._observed_events.append({'event_name': event_name, 'callback_fn': callback_fn})
    def forget(self, event_name):
        for dict_item in self._observed_events:
            for key, val in dict_item.items():
                if val == event_name:
class Event():
    def __init__(self, event_name, *callback_args):
        for observer in Observer._observers:
            for observable in observer._observed_events:
                if observable['event_name'] == event_name:

Here is example of how to use this library
import EventObserver
# class object MUST inherit Observer object if you use it within class
class Room(Observer):
    def __init__(self):
        print("Room is ready.")
        Observer.__init__(self)  # DON'T FORGET THIS
        # observer can be declared already in class init method with following line
        # this.observe('someone sneezed', this.someone_sneezed)
    def someone_arrived(self, who):
        print("{} has arrived!".format(who))
    def someone_sneezed(self, who):
        print("{} has just sneezed!".format(who))
# Observe for specific event
room = Room()
room.observe('arrived', room.someone_arrived)
room.observe('sneezed', room.someone_arrived)
# Fire some events
Event('left', 'John')       # no events are attached to event "someone left" 
Event('arrived', 'Lenard')  # will output "Lenard has arrived!"
Event('sneezed', 'Jenny')   # will output "Jenny has just sneezed!"
# Remove known event
# no events based on 'someone arrived' will be fired

RC Plane telemetry

I never forgot my old dream- to have my own DIY telemetry system

And here after like 7 years, when technology advanced (my knowledge, also)- I have finished building my project. And my main problems are solved with two unit of ESP32 microcontrolers and Android phone. Hardware is two ESP32 units with integrated SX1278 interface and one Beitian BN-220 GPS and GLONAS receiver.

I dont realy like C programming, so my choise of microcontroller was based on availability to use other languages for programming. Initial idea was to use Espruino firmware and use Javascript language for programming. But the issue at the time of research was BLE interface was not available (Harware supports it). Other options was Micropython and LUA. I have burned Micropython firmware into ESP32

So, here is how everything works: microcontroler ESP32 read GPS receiver data, extract required informaation and… taaadaaaa… =)

LoRa is used to transfer data to ground unit. Once i've tested range of my LoRa equiped ESP32's units- I've received over 2.2 km LOS at 433mhz. As i'm flying my plane in line of sight- it's plenty for me.

Ground unit listend for air unit frequincy, extract data and via BLE interfaace share this information with my Android device. Device application is created using Droidscript.

Each time i'm testing something new, like programming language, i choose to build solution that would help in my life. This way I can learn more about tool, test is it suitable for me and solve my issue if I succeed.

Compile APK online

It was long time i was dreaming about ability to compile apk online. So this blog post (tutorial) will be how to prepare C9 (C9 was bought by Amazon AWS and does not really offer free containers any more) or Goorm online IDE or any similar based on ubuntu linux to be able to develop online. This should also work on local linux installation or even Windows subsystem for Linux if you are on Win10

This post will not be about “upload my zip online and get apk”. You have to set up environment in virtual server. My suggestion is go with Goorm IDE they give you up to 5 containers for free where you can set up different environment for various development things.

First of all, create new empty ubuntu box and resize it to 1Gb RAM and 5GB storage goorm gives you 1GB ram and 10GB storage out of the box. Simple APK compile stull will require about 1GB of storage, but if you decide to go on gradle dependency management system- storage will grow to 2.5GB.

Prepare your system

I prepending everyhing with sudo command, in case any permission will be missing.

So lets begin from very basic. At first you need JAVA, so add OpenJDK repository and install java

sudo add-apt-repository ppa:openjdk-r/ppa
sudo apt-get update

Install Java headless, because you do not need GUI here

sudo apt-get install openjdk-8-jdk-headless

Download SDK zip from android home. You may use my provided link


Make directory for android SDK and extract ZIP

sudo mkdir -p /opt/android-sdk
sudo unzip -d /opt/android-sdk

Now add environment variables to your system.

sudo nano /etc/profile

and at the very end add following lines

Always check if copying from website does not ruin you double-quotes

export ANDROID_HOME="/opt/android-sdk"
export JAVA_HOME="/usr/lib/jvm/java-1.8.0-openjdk-amd64"
export PATH=$JAVA_HOME/bin:$ANDROID_HOME/tools/:$ANDROID_HOME/platform-tools/:$PATH

Save and exit by pressing CTRL+X on keyboard and confirming that you want to save changes by Y. Restart your machine or environment.

Now you need to add SDK, Tools and platform stuff. I have chosen 24 version so i have used this command

sudo /opt/android-sdk/tools/bin/sdkmanager "tools" "platforms;android-24" "build-tools;24.0.3"

in case you want something else or want to see available list use sdkmanager –list command

Looks like everything is prepared, now need “Hello world!” android application. You may need to prepare it according structure and create all files or You can download this HelloAndroid project and extract in in your workspace.

Steps needs to be done to get APK file

  1. Generate file AAPT
  2. Compile java file with javac
  3. Translate it to Dalvik Bytecode with DX
  4. Make apk with AAPT
  5. Align apk package with ZIPALIGN
  6. Sign your apk file with APKSIGNER

AS you can see, there is a step to sign you apk install file with certificate. You can create your own. In main project directory, the same where AndroidManifest.xml file exist, run following command to create private key:

keytool -genkeypair -validity 365 -keystore mykey.keystore -keyalg RSA -keysize 2048

Answer all questions and provide password.

Thats it. Now you can create APK file from command line. To create automated, here is prepared bash script witch you should save in project root directory (the same as android manifest) and run to build your project. I have chosen to name it
set -e
echo "Cleaning..."
rm -rf obj/*
rm -rf src/in/ignas/helloandroid/
rm -rf bin/*
echo "Generating file..."
$AAPT package -f -m -J src -M AndroidManifest.xml -S res -I $PLATFORM
echo "Compiling..."
javac -d obj -classpath src -bootclasspath $PLATFORM -source 1.7 -target 1.7 src/in/ignas/helloandroid/
javac -d obj -classpath src -bootclasspath $PLATFORM -source 1.7 -target 1.7 src/in/ignas/helloandroid/
echo "Translating in Dalvik bytecode..."
$DX --dex --output=classes.dex obj
echo "Making APK..."
$AAPT package -f -m -F bin/hello.unaligned.apk -M AndroidManifest.xml -S res -I $PLATFORM
$AAPT add bin/hello.unaligned.apk classes.dex
echo "Aligning and signing APK..."
$ZIPALIGN -f 4 bin/hello.unaligned.apk bin/hello.apk
$APKSIGNER sign --ks mykey.keystore bin/hello.apk

In case you have used different versions in sdkmanager command- edit path in header accordingly. Just run this script with following command. If you can not run it chmod +x


Script will ask password for your keystore that you provided earlier.

This solution works if your application does not have any dependencies on external libs and gradle wrapper is not used. Probably, automated install script can be made but that's for another times. In case you have any suggestions, comment or anything worth to say- comment below.

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  • blog.txt
  • Last modified: 2023/11/07 13:33
  • by Ignas