27. November 2016

Controlling relay connected to ESP8266 via MQTT from Android

After successful implementation of MQTT into Lamp Relay with ESP8266 there was one remaining challenge. Communication of Android Lamp App with ESP8266 via MQTT. It was little bit harder than I expected, because examples were not very clear.

Sending commands to MQTT broker was relatively easy. There was just a catch. It is necessary to declare the MQTT service in AndroidManifest.xml:

<service android:name="org.eclipse.paho.android.service.MqttService">

Thanks to tutorial from HiveMQ I was able to send messages to MQTT broker.

The problem was the opposite direction. How to receive messages?

Well, there is support in the same MQTT library for topic subscriptions. The issue is that incoming message is being processed on background thread and it’s not possible to update UI. It took me some time to realize the source of problem. I was hunting ghosts. I thought that there is some problem in ImageButton or TobbleButton.

Correct solution was to move communication to Android service class. Then bind the service so UI can send commands to the service and the last part was to add broadcast receiver to pass message from service to UI.

Here is small schema which describes delivery of message from broker to app.


It was necessary to make also small update in ESP8266 in order to tell Mosquitto to persist the state of a lamp (the last bool parameter):

mqttClient.publish(topicName("relay"), "off", true);

The result is nice. I can turn on the lamp via web interface and all connected Android apps are updated and user can see the state of the lamp.


The code for Android app is available at Github – LampApp. Previous code with REST API was moved to branch v0.1. The code for ESP8266 module is also at Github – LampESP. Feel free to customize the app. You can find instructions in README.md.

I see the next challenge for LampApp: display lamp control widget at lock screen. Maybe I’ll be more successful than the last time.

12. November 2016

Android widget not visible on Lenovo K5 – Solved

I’ve created Android Widget for controlling ESP8266 relay the last week.


The only problem was that the widget was not visible on Lenovo K5.

I was searching for the root cause using method: “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

I grabbed several other repositories with widgets from Github. Widgets from other projects were working.

To keep long story short. Here is the configuration when widget does not appear:


Here is the configuration when widget properly appears:


Can you spot the difference?

It is very simple. Large number of Android devices displays widget just after installation even when using the first configuration. The problem with Lenovo K5 is that it does not register widget just after installation via adb. You need to launch MainActivity and only after that UI subsystem displays the widget.

Original code from Obaro’s repo is without MainActivity. I took inspiration from Udacity’s Android widget. After I’ve added MainActivity and several other small files into the project the widget appeared even on Lenovo K5.

You can find updated version at GitHub/LampWidget. Thanks to Adusak for a hint about MainActivity.

6. November 2016

Controlling lamp with ESP8266 via WiFi by Android Widget

Two weeks ago I made research about available Smart Home Power Sockets. The result was not very positive.

Week ago I discovered talk about ES8266 which seemed to be the right solution.

And what about this week?

I happy to report success. I am able to control the lamp from mobile phone. 🙂

This week I bought WeMos D1 Mini WiFi ESP8266 and relay. Together with friend we soldered few pins and wrote some code. The solution was working immediately after we plugged it into a wall.

Here is the result:


Code for Arduino is derrived from esp8266learning.com:

//This example will set up a static IP - in this case
#include <ESP8266WiFi.h>

const int relayPin = D1;
const int chipSelect = D8;
const char* ssid = "MYSSID";
const char* password = "SECRET";
WiFiServer server(80);
IPAddress ip(192, 168, 1, 50); // where xx is the desired IP Address
IPAddress gateway(192, 168, 1, 1); // set gateway to match your network
void setup() {
  pinMode(relayPin, OUTPUT);
  Serial.print(F("Setting static ip to : "));
  // Connect to WiFi network
  Serial.print("Connecting to ");
  IPAddress subnet(255, 255, 255, 0); // set subnet mask to match your network
  WiFi.config(ip, gateway, subnet); 
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
  Serial.println("WiFi connected");
  // Start the server
  Serial.println("Server started");
  // Print the IP address
  Serial.print("Use this URL : ");
void loop() {
  // Check if a client has connected
  WiFiClient client = server.available();
  if (!client) {
  // Wait until the client sends some data
  Serial.println("new client");
  // Read the first line of the request
  String request = client.readStringUntil('\r');
  // Match the request
  int value = LOW;
  if (request.indexOf("/relay=on") != -1) {
    digitalWrite(relayPin, HIGH);
    value = HIGH;
  if (request.indexOf("/relay=off") != -1){
    digitalWrite(relayPin, LOW);
    value = LOW;
  // Return the response
  client.println("HTTP/1.1 200 OK");
  client.println("Content-Type: text/html");
  client.println(""); //  do not forget this one
  client.println("<!DOCTYPE HTML>");
  client.print("Led pin is now: ");
  if(value == HIGH) {
  } else {
  client.println("<a href=\"/relay=on\">Relay ON</a><br>");
  client.println("Click <a href=\"/relay=off\">Relay OFF</a>");
  Serial.println("Client disconnected");

That was the easy part. I was able to control relay directly from mobile phone via web browser which was not very convenient. The widget would serve better.

Writing a widget for Android was real challenge. There is very little documentation about it and even Android Studio does not contain template for writing widget. I spent several hours learning how widget works. It is very different from common application.

The very first gotcha that costed me more than a hour was very common problem with builds:

Error:(3) Error retrieving parent for item: No resource found that matches the given name 'android:TextAppearance.Material.Widget.Button.Inverse'.

Yes, it is very clear where is the problem. Or not? 🙂

It is necessary to fix build.gradle and set proper version of compile dependency. In my case I was targeting API 22, but appcompat was set to 23:

dependencies {
    compile 'com.android.support:appcompat-v7:22.1.1'

The real fun begins with the widget code. I cobbled together several chunks of code. Primary source was Obaro’s SimpleAndroidWidget and android-async-http.

Here is the very crude code for Android:

package com.sample.foo.simplewidget;

import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.widget.RemoteViews;

import com.loopj.android.http.AsyncHttpClient;
import com.loopj.android.http.AsyncHttpResponseHandler;

import cz.msebera.android.httpclient.Header;

public class SimpleWidgetProvider extends AppWidgetProvider {

    private void getHttpRequest(String state) {
        AsyncHttpClient asyncClient = new AsyncHttpClient();
        asyncClient.get("" + state, new AsyncHttpResponseHandler() {
            public void onStart() {

            public void onSuccess(int statusCode, Header[] headers, byte[] responseBody) {


            public void onFailure(int statusCode, Header[] headers, byte[] responseBody, Throwable error) {



    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        final int count = appWidgetIds.length;

        for (int i = 0; i < count; i++) {
            int widgetId = appWidgetIds[i];
            String value = "off";
            SharedPreferences prefs = context.getSharedPreferences("LampApp", 0);
            boolean isRelayEnabled = prefs.getBoolean("relayState", false);
            isRelayEnabled = !isRelayEnabled;
            SharedPreferences.Editor editor = prefs.edit();
            editor.putBoolean("relayState", isRelayEnabled);

            if (isRelayEnabled) {
                value = "on";

            RemoteViews remoteViews = new RemoteViews(context.getPackageName(),
            remoteViews.setTextViewText(R.id.textView, value.toUpperCase());

            Intent intent = new Intent(context, SimpleWidgetProvider.class);
            intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS, appWidgetIds);

            PendingIntent pendingIntent = PendingIntent.getBroadcast(context,
                    0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
            remoteViews.setOnClickPendingIntent(R.id.actionButton, pendingIntent);

            appWidgetManager.updateAppWidget(widgetId, remoteViews);


That’s not all. When you want to create widget you need to define also special handling in AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    <uses-permission android:name="android.permission.INTERNET" />

    <application android:allowBackup="true" android:label="@string/app_name"
        android:icon="@mipmap/ic_launcher" android:theme="@style/AppTheme">

        <receiver android:name="SimpleWidgetProvider" >
                <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
            <meta-data android:name="android.appwidget.provider"
                android:resource="@xml/simple_widget_info" />



Even that is not enough. You’ll need several small files in res directory including graphics. I won’t describe them here. You can download it from GitHub repo georgik/LampAndroidWidget.

The result?


It works perfectly on Samsung Galaxy S5 Neo, but for some reason I was not able to display this widget on Lenovo K5. If you have any idea why Lenovo K5 has such issue, let me know.

I also discovered a bug in the code of widget. When you have more than one widget it starts turning on and off the relay several times depending on number of widgets 😉

The solution is ok for the time being. I’m already thinking about using MQTT and Node-Red which was discussed this weekend at OpenAlt conference in Brno by guys from McGayver Bastlíři SH.

22. March 2014

Kivy – buildozer android debug failed with libstdc++.so.6: cannot open shared object file

Kivy is awesome library for developing GUI applications in Python.

It’s possible to build same application for desktop, Android or iOS. It’s something like Cordova/PhoneGap for JavaScript.

I was following Kivy crash course 2: Building an android apk tutorial recorded by Alexander Taylor.

I was trying to build application on Linux Debian for Android:

buildozer android debug

Build failed with quite strange message:

[mergemanifest] Manifest merger disabled. Using project manifest only.
     [echo] Handling aidl files...
     [aidl] Found 1 AIDL files.
     [aidl] Compiling 1 AIDL files.
     [aidl] /home/georgik/.buildozer/android/platform/android-sdk-21/platform-tools/aidl: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory


assets/private.mp3: /home/georgik/idea/kivytest/.buildozer/android/app/sitecustomize.pyo
Traceback (most recent call last):
  File "build.py", line 431, in 
  File "build.py", line 346, in make_package
    subprocess.check_call([ANT, arg])
  File "/usr/lib/python2.7/subprocess.py", line 540, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['ant', 'debug']' returned non-zero exit status 1

The reason of this problem is not so obvious.

My operating system is 64bit, but Android build system requires 32 bit version of stdc++ library.

Fix is very easy. Just install lib32stdc++6 package 🙂

apt-get install lib32stdc++6

If build is still failing, because of other missing libraries, then you can use online Debian package search to find missing dependencies: https://www.debian.org/distrib/packages

Other missing 32bit libraries are often libz, libncurses5:

apt-get install lib32z1 lib32ncurses5

8. January 2014

The story behind PF2014 – Cordova – slides

Slides available in formats: PDFSlideShare

Web version: http://pf2014.sinusgear.com
Mobile versions: Android, App Store, Amazon
Source code: GitHub