Home Automation System - My first sensors...

After all my experiments, now I'm able to use OpenHAB with familiarity; so now it's time to build my first sensors.

Let's start from the kitchen where I would like to monitor gas, temperature and humidity.

The MCU will be a ESP8266 NodeMcu board. I chose this board because it has wifi, several digital I/O and an analog one, you can write firmware in the same way you could with Arduino and above all...it's very cheap...On Banggood I bought two at only € 2,76 each, not bad...

If you are interested in it, this is the product link:

Geekcreit-Doit-NodeMcu-Lua-ESP8266 on Banggood.com

I will use these sensors:

- MQ-4 gas sensor: for detecting of methane mainly, (I'm interested on it...), propane and butane gas. I already used it months ago. Here is it:

MQ-4 gas sensor on Banggood.com

- Humidity / Temperature sensor DHT11: it'a a very cheap sensor (with about €5 i bought 5); its error is +/- 2°C and it's able to get only positive temperature. Its precision is 1°C, so no decimal number...For these limitations I decided to buy other sensors, the ds18b20 (for internal and external use)...I will use these DHT11 just for humidity

5 pack on Banggood.com

3 Pack on Banggood.com

Single sensor on Banggood.com

- Dallas ds18b20 temperature sensor: compared to the previous one it has a better precision (0,5°C) and it's able to get negative values, so it's ideal for external use

Single sensor on Banggood.com

5 Pack on Banggood.com

External probe on Banggood.com

I built some prototype using a breadboard...

...till I found the right configuration...and so I made a "definitive" board...

I added a led used for the indication of network activity and a connector used for external power. The device will be powered through a little 5V 450mA power adapter, connected to the blue terminal blocks. In this way I could power up the device and also the sensors.

The led, ds18b20 and DHT11 sensors are linked to digital I/O and the MQ-4 gas sensor to the analog one.

Now it's time to write the firmware...I use Visual Studio Code with platformio extension; I think it's better than the Arduino IDE (personal opinion). I chose this IDE because it also has an extension for openHAB that let me edit configuration files in a better way (just like Eclipse SmartHome Designer).

My device will connect to the MQTT broker of OpenHAB through wifi, fetch the data from the sensors and send them as json formatted string with nodemcu/mainfloor/esp8266mcu11/temphumiditygas/state topic.

The sample period is 5 seconds and each 60 seconds the average data will be sent to the MQTT broker. When the data will be sent, the green led will blink twice.

Here is an example of a message sent to the MQTT broker:

{"gas":{"error":"","sensorValue":46.33333,"ppm":0.431016,"percentage":0.000043,"realValue":829.0371},"tempHum":{"error":"","humidity":63.66667,"tempC":22,"tempF":71.59999,"heatIndexC":21.91774,"heatIndexF":71.45234},"temp":{"error":"","tempC":21.66667,"tempF":70.99999}}

The gas object is related to the MQ-4 sensor, the tempHum object is related to the DHT11 sensor and the temp object is related to the ds18b20 sensor.

For now I decided to use both sensors for temperature reading; so I can compare them.

Ok, it seems to work as expected...I put my device in the right place in the kitchen...

Now it's time to setup OpenHAB...and build a new dashboard on Grafana.

In OpenHAB I created a new file called esp8266mcu11.items (esp8266mcu11 is the unique id of the device) in the /etc/openhab2/items folder; in this file I appended the following lines:

Number MainFloor_KitchenTemperature "Kitchen Temperature [%.1f °C]" <temperature>
(gPersistence)
{mqtt="<[openhabianpi-mqtt:nodemcu/mainfloor/esp8266mcu11/temphumiditygas/state:state:JSONPATH($.tempHum.tempC)]" }

Number MainFloor_KitchenTemperatureNew "Kitchen Temperature NEW [%.1f °C]" <temperature>
(gPersistence)
{mqtt="<[openhabianpi-mqtt:nodemcu/mainfloor/esp8266mcu11/temphumiditygas/state:state:JSONPATH($.temp.tempC)]" }

Number MainFloor_KitchenHumidity "Kitchen Humidity [%.1f %%]" <humidity>
(gPersistence)
{mqtt="<[openhabianpi-mqtt:nodemcu/mainfloor/esp8266mcu11/temphumiditygas/state:state:JSONPATH($.tempHum.humidity)]" }

Number MainFloor_KitchenGasPpm "Kitchen Gas [%.2f ppm]" <carbondioxide>
(gPersistence)
{mqtt="<[openhabianpi-mqtt:nodemcu/mainfloor/esp8266mcu11/temphumiditygas/state:state:JSONPATH($.gas.ppm)]" }

Number MainFloor_KitchenGasValue "Kitchen Value [%.2f]" <carbondioxide>
(gPersistence)
{mqtt="<[openhabianpi-mqtt:nodemcu/mainfloor/esp8266mcu11/temphumiditygas/state:state:JSONPATH($.gas.realValue)]" }


Now the sitemap:

Frame label="Gas Detection" {
Text item=MainFloor_KitchenGasPpm valuecolor=[>800="red",>600="orange",<=600="green"]
}

Frame label="Kitchen" {
Text item=MainFloor_KitchenTemperatureNew
Text item=MainFloor_KitchenHumidity
}

And this is the result:

Good, I added a new brick...now I can create the new Grafana dashboard with the gas, humidity and temperature of the kitchen:

Last step: adding the device to the network monitoring...so OpenHAB will notify me when the device will be offline.
So, using PAPERUI I added the device using the Network Binding and create the items. Then I added the gNetworkCheck group to the "status" item, so its network presence will be monitored by OpenHAB.

Data Acquisition - Remote Gas Detector

Now, it's time to connect a remote sensor to my new receiver and begin a real data acquisition.

I think I'll go back to my sensor gas prototype...I already made some experiments with it:

First experiment: a simple gas detector

I'm going to use it as a remote gas sensor with MQ-4 [Datasheet].

and a wireless RF-433 transmitter.

with a lot of wire, led and a push button to reset sensor status.

HARDWARE

This is the fritzling design:

As well as Wireless transmitter and gas sensor, we could see a red led, a green led and a RGB led. On the left side of the schema, there is also a push button. Led are powered by Arduino 5V power line, protected by resistors...Arduino is powered by a 12V transformer just like the wireless transmitter, to ensure the best transmission power.

PIN 11: push-button

PIN A1: analogue pin linked to GAS sensor

PIN 9: wireless data transmission

PIN 12: red led for wireless activity indication
PIN 8: green led for data acquisition activity
PIN 3, 5 and 6: RGB led for showing system status
 - off: normal values;
 - yellow: an out of tolerance value under the danger threshold;
 - rosso: an out of tolerance value over the danger threshold;

Here is it:

FUNCTIONALITY AND MESSAGES

When the system is powered up, the gas sensor warm up stage starts; this is necessary to ensure better precision...during this time, RGB led blinks.

Then, data acquisition starts.

Every second the system gets 10 samples data from the sensor (the green led flashes every second) and calculates the average...Every 5 seconds the average of the collected values is sent to the receiver (the red led flashes every 5 seconds).

When the average is out of tolerance, RGB led lights up.

The push buttons reset the system status and turns off the RGB led. If a value is out of tolerance and then other samples return to normal values, the led still lights on...to get the attention...only through the push button, led could be turned off.

The wireless data sent every 5 seconds is a text string with the following format:

GAS;VALUE;STATUS|

VALUE is the calculated average, STATUS is a numeric value indicating the system status according to the following schema:

 - 1: ok;
 - 2: warning
 - 3: danger

SOFTWARE

You can download the complete Arduino Sketch from here:

DOWNLOAD

As for the receiver, I used RADIOHEAD libraries to manage wireless transmitter.

Setup:

- wireless receiver setup;

- status led setup;

- MQ-4 sensor warm up;

Main loop:

- First, the system checks the push button status...If it was pressed, the variable which manages the system status will be set to OFF;

- Then, the system read 10 samples from the gas sensor and calculates their average; during this time the green led lights up (PIN 8);

- Every 5 seconds the system calculates the average and set the system status according to this value; then, this value is sent to the receiver;

- In case of out of tolerance value, RGB status led (PIN 3, 5 e 6) will light up;

- The average value is sent to the receiver; during this time the green led (PIN 12) will light up;

And finally, here is a short video:

First experiment: a simple gas detector

Let's begin assembling some stuff from starter kit...as first example we will try to build a simple "gas detector" using MQ-4 sensor.

Here is the datasheet

The sensor has 3 pins:

- Vcc: 5V supply voltage, Arduino friendly;
- GND: ground connection;
- AD: analog output; provides a value congruent with the gas concentration in the air;
- D0: triggered digital output; provides an HIGH signal when the gas concentration exceeds a limit; you can set this limit through the trigger;

We will use only the analog output, which will be linked to an Arduino's analog input pin.

The sensor needs a pre-heating time.

In our prototype, just for example, we will use also:

- a temp sensor: LM 35
- an LCD display 16X2 backlighted with Hitachi HD44780 driver
- a Buzzer
- a led
- a pot

On the display we will show datas provided by the sensors; led and buzzer will be used to signal warnings and alerts and the pot controls the LCD display dimmer.

Here is the demonstration video: