Measuring Room Conditions (II)


To get data from several measuring stations I implemented MQTT on DHT11/D1 mini-Module publishing temperature and humidity data to a MQTT broker.

To monitor these data I use myMQTT Android app on my Galaxy S5 and subscribed to the topic DHT11/+/# to see all messages send with the topic DHT11/<ESP-ID>/temperature, DHT11/<ESP-ID>/humidity and DHT11/<ESP-ID>/state.

The screenshot from that app shows temperature and humidity values sent by two sensor nodes with the ESP-ID ESP8266-1138645 and ESP8266-1138432.

As subscriber node I used a NodeMCU LoLin board which sends each minute the message “in operation” to the topic DHT11/<ESP-IS>/state. This messages is usefull to monitor the operation of such a subsriber node remotely. The screenshot shows this state sent by the node with the ESP-ID ESP8266-14695321.

These ESP-IDs are generated automatically from device ID.

The program samples dht_mqtt.lua and dht_subtemp.lua can be found at Sourceforge.

Measuring Room Conditions (II)

Measuring room conditions

thermo_hygrometerTo measure the room conditions we can use a traditional Thermo-Hygrometer as shown in the image.

If you want to see these conditions from any location around your home then you can use a cheap DHTxx shield connected to a D1 mini and dweet its data to Use to make these data visible at any location. The program sample dht_dweet.lua can be downloaded from Sourceforge.

You can use your smartphone or a tablet to visualize the room conditions of the observed room (


Further information on NodeMCU and ESP8266 devices in “Building an IoT Node for less than 15 $” (;

Measuring room conditions

Last Phase

CoverThe analyst firm Gartner says that by 2020 there will be over 26 billion connected devices…that’s a lot of connections (some even estimate this number to be much higher, over 100 billion).

The IoT is a giant network of connected “things” (which also includes people).  The relationship will be between people-people, people-things, and things-things. The new rule for the future is going to be, “anything that can be connected, will be connected.”

In this book I will consider the frontend of the IoT – the so-called IoT node. This IoT node is connected to sensors and actors and to the network. Our IoT node here uses WLAN connectivity to the network by which it is very easy to integrate it in an existing office or home network.

This task can be fulfilled by a lot of wireless network capable microcontrollers as Arduino, Raspberry Pi, Beagle Bone and further more equipped with a Wifi device. But the use of such complex devices is not in focus here. Our goal is to use a very cheap device to build a compact IoT node.

The title of this book defines our goal – building an IoT Node for less than $ 15. A listing of expecting costs for the various components is given in the IoT Node Costs.

The ESP8266 microcontroller is the base for this journey.

The book is scheduled to appear in the autumn 2015. Here is the table of content. If you are interested in more details please leave a replay.

Last Phase