Reading the DHT11 or DHT22 on the Raspberry via an overlay and send it to the openHab REST API

In an earlier tutorial I showed how to read the popular DHTxx sensor on a Raspberry Pi and then to MQTT that into Openhab.
However, there are more ways to skin a cat, so what I like to do this time is:

1) Read the sensor with a device tree overlay on a Raspi and then
2) Send the data to OpenHab with the REST-API

I am not saying one method is better than the other, but suppose you dont want to install an MQTT server because all your other channels don’t need MQTT, then the REST API comes in handy.

1) Reading the DHT sensor
First we need to load the dht11 overlay at boot-up
Do
sudo nano /boot/config.txt
and add:

dtoverlay=dht11,gpiopin=4

obviously one can pick another pin here, or declare a different sensor such as the DHT22 or DHT21 (AM2301)

then all you have to do is to read the following 2 files:

/sys/devices/platform/dht11@0/iio:device0/in_temp_input
/sys/devices/platform/dht11@0/iio:device0/in_humidityrelative_input

Once you have loaded the overlay and connected your sensor, a simple:
cat /sys/devices/platform/dht11@0/iio:device0/in_temp_input,
would show you the temperature.
whereas:
cat /sys/devices/platform/dht11@0/iio:device0/in_humidityrelative_input, would show you the humidity

Upon doing that in a python program, I noticed there can be quite a number of I/O errors. This seems to be a frequent problem with this overlay, so in order not to interrupt the program, I had to do a bit of Error catching.

2) Sending values to OpenHab
The REST API is fairly simple to use. We only need 1 line for every Item we want to update. Such a line looks like this:
requests.put('http://192.168.xxx.yyy:800/rest/items/<YOUR ITEM>/state',value).
The ‘value’-variable needs to be a string.

3) Wrapping it up
A simple Python program would look like so:

import time
import requests
tfile='/sys/devices/platform/dht11@0/iio:device0/in_temp_input'
hfile='/sys/devices/platform/dht11@0/iio:device0/in_humidityrelative_input'

def read_temp_raw():
   f=open(tfile,'r')
   lines=float(f.read())/1000.0
   f.close()
   return lines

def read_humidity_raw():
   b=open(hfile,'r')
   hlines=float(b.read())/1000
   b.close()
   return hlines

while True:
   try:
     T=str(read_temp_raw())
     print(T)
     H=str(read_humidity_raw())
     print(H)
     time.sleep(2)
     #Put your own IP and Itemnames here,
     requests.put('http://192.168.1.103:8080/rest/items/<ITEMNAME>/state',T)
     requests.put('http://192.168.1.103:8080/rest/items/<ITEMNAME>/state',H)

   except IOError:
      print("I/O error")

Beware that Python programs rely on proper indenting. As this sometimes can be corrupted by publication on a website, I will leave an image of the properly indented program below:

As I am not the world’ s best python coder, I am sure improvements can be made, but at least this code will get you up and running fast.
Since the items are updated through the REST API, they do not need a channel and could look as simple as this:

Number HH "REST Humidity [%.0f %%]" <humidity> (Weather)
Number HT "REST temperature [%.1f °C]" <temperature> (Weather)
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Boot problems after mounting a USB stick on a Raspberry Pi Zero

This will just be a short piece, more like a tip to take into consideration.
While playing around with a Raspberry Pi Zero W, I had inserted  a USB OTG ‘hub’  that could take a micro SD card and a USB stick and I had mounted the medium that was in there.
My goal was to use the USB stick to write picture files from a security camera to, in order to spare the SD card.
As also my ordered headers arrived, I shut down the Raspberry, soldered the headers and started up again.
To my horror, it wouldn’t start. Fearing that my soldering somehow had damaged the raspberry Pi, I exchanged cards with a Raspberry Pi B and restarted both. Thank god, the ‘start problem’  was related to the card, not the raspberry.
But how was that possible. It was a new card, and I always had properly shut down the raspberry it was in.
Then it dawned on me, could it be… no it couldn’t, could it??
I realised that after soldering, I had not reinserted the OTG hub with USB stick anymore. Could that be the problem??
After re-inserting the OTG hub with USB stick, my Zero started immediately again.
Obviously that is not the behaviour I want. I will see if I can do something about it, but for now I removed the mount.

 

Controlling a GPIO pin on a remote raspberry

In an earlier post I showed how one could address the raspberry GPIO pins from within OpenHab (or NodeRed for that matter). The only limitation here was that it was on a raspberry that also hosted OpenHAB.

What if you have a RaspberryPi whose pins you want to control from within OpenHab, while openHab is in fact operating from another machine?

In that case  MQTT seems the best option. I wrote a Python program that will do just that.
If you installed Jessie or Stretch, it comes already with Python 2.7 which is quite suitable for this goal.
You will need two libraries:

The lightweight MQTT client Eclipse Paho Mqtt: Here I describe how to install it, but you could also just do:
pip install paho-mqtt

The second one you need to install is the Rpi.GPIO library.
LadyAda gives a good explanation  how to do that, but it basically comes down to issuing the command:
sudo apt-get install python-dev python-rpi.gpio

The Python program itself is fairly simple, but there are a few things to point out
The Rpi.GPIO library has two modes to set up the pins. it has ‘BCM mode’ and ‘BOARD mode’
These two modes refer to the numbering of the pin.

The GPIO.BOARD option specifies that you are referring to the pins by the number of the pin in the plug – i.e the numbers printed on the board.

The GPIO.BCM option means that you are referring to the pins by the “Broadcom SOC channel” number, these are the numbers after “GPIO” that can be seen in the various pinout diagrams

If you are still a bit puzzled, you can try and issue “the gpio readall” command on your terminal and depending on the type of Raspberry you have, you may get outputs like this for the Rpi3:

or this one for the B+
You will also need to set the IP for your particular MQTT broker and need to change the topic according to your wishes.

The program currently switches one pin ON or OFF. it is not particularly hard to expand that for more than one pin. The working can be controlled by the gpio readall command (check in the column ‘V’ what the state of the pin is)

I saved the program in my home/pi directory. It can be started by
python mqttpublish2.py (or any other name you want to give it). It is best to have it start at boot-up
Output will look like this:
A slight word of warning: Python sees indents as part of the command structure. If after downloading my file you go change it, be careful not to mess up the indents.
Edit: In the mean time I expanded the program a bit, it now sends the state of the pin as a seperate topic. It also sends the IP nr, the program name and an ‘alive’ message on startup. It uses pin 18.

 

Battery fed Deepsleep Weatherstation revisited

After my previous publication of a battery fed weatherstation, I exchanged ideas with one of the commenters about ways the improve the energy efficiency of the circuit.

One doesn’t need to be a rocketscientist for that:
Ditch the batteryshield as it is very inefficient
Ditch the DHT22 as that constantly uses 2.5mA
Ditch the Wemos as even while it is in deep sleep the CH340 chip on the board isn’t. (it drains 200uA)
Ditch the voltage divider used to monitor the battery voltage (it drains 10uA).
Also ditch the BMP280 as it cannot measure humidity.

So what we will be doing is use a bare ESP8266-12F  and a BME280 as that can measure humidity as well as temperature and airpressure.
Feed with alkaline cells, omitting the need for an LDO. That way the voltage can be measured directly from Vcc/Vbatt without the need of a voltage divider

So, a new circuit starts to evolve:

Obviously that needs a bit more soldering than just using a Wemos and battery shield, but in essence one only needs to add the resistors to put the necessary pins HIGH (pins 0, 2 and CH_PO) or LOW (pin 15). There are however  various baseplates  for the ESP8266-12F that have these resistors already present. The  capacitor is  there to give some extra boost when the ESP is busy connecting to a network.

In order to minimize the poweruse of the BME280, one has to use some special settings. Normally the BME280 constantly is taking readings of its sensors. Not only does that take more power, but I noticed it can also drive up the temperature of the chip, influencing the temperature reading.
The mode to use it in is  the so called Forced Mode: it will only take a reading when told to do so.
Now mind you, even if you don’t tell it to take a reading, the library will still give you a result as that gets its values from a register, but it will always be the same value, you will need to tell the chip it has to store a new value in that register.

The datasheet suggests 4 different possibilities of ‘Forced mode’:

  • Weather station scenario
  • Humidity scenario
  • Indoor Navigation
  • Gaming

We obviously will be taking the first one.
The software can be downloaded here

While in sleep this should draw 80uA
Now suppose we have a 2000mAh battery then the circuit could run 25000 hour=1042 days=2.85 years =2 years, 10 months and a week
Now obviously that is a bit of a simplification as the full power of the battery might not be available within the 4.2<->3.0 Volt slot and ofcourse the circuit is using more current when not asleep, so lets recalculate:
Though larger peaks exist, the average current drawn during connection is some 85mA. So suppose that we have a 3 second connection and 15 (900sec) min of sleep
The current consumption is then as follows 3x85mA+900x80uA=255+72=327mAs, so over an hour it consumes 1308mAs and during a day 31392mAs. So every day that is 8.72mAh. A 2000mAh battery then gives 229 days=7.6 months.

 

 

Read a DHT sensor on Raspberry Pi and mqtt the results

In an earlier post I showed how one could address the raspberry GPIO pins, in fact that is quite straightforward given the fact they are digital I/O pins that either are HIGH or LOW.
But what if one wants to read a sensor like a DHT11 attached to one of the GPIO pins? That is also not so difficult, but to make it more all round and easy to use in OpenHAB, I wanted to read a sensor and then MQTT the result to my MQTT broker.
In my case, my MQTT broker is on the same raspberry that I also aimed to attach the DHT11 to, so if I wanted I could read it directly, but just in case I wanted to read it from another raspberry, MQTT is a better solution (for me).

As it is no use to re-invent the wheel, I fortunately found someone already had done most of the work, albeit for a DHT22, but that was easy to alter.

For the next steps I presume you already have python installed. Jessie already should have python 2.7 installed, and should you want to upgrade that, check here.
The Python program calls a few libraries that you most likely already have, maybe with exception of the paho.mqtt.client and the adafruit DHT library.
the mqtt client can be installed as follows:*)
pip install paho-mqtt
if for whatever reason this does not work for you, try:
git clone https://github.com/eclipse/paho.mqtt.python.git => download the client
cd paho.mqtt.python => go to proper directory
python setup.py install => install the client
depending on how you are logged in you may need to add ‘sudo’ before the install commands

The mqtt client is now installed.

For the DHT library do the following:
git clone https://github.com/adafruit/Adafruit_Python_DHT.git => download the library
cd Adafruit_Python_DHT => go to proper directory

Before you install the library, you need some dependencies that may or may not be on your system:
sudo apt-get update
sudo apt-get install build-essential python-dev python-openssl
If you already had modules installed those will be skipped.
Then install the library:
sudo python setup.py install => install the library

At this moment it is a good idea to restart your raspberry.
If you want -when your raspberry is back up and running- you could now try one of the example programs in the Adafruit DHT library, just to make sure everything is working.
Connect your DHT11 to e.g. GPIO4 of your raspberry.
Make sure you are still in  directory: Adafruit_Python_DHT

do:
cd examples
sudo ./AdafruitDHT.py 11 4

You will get the temperature and Humidity reported in your terminal

Now download the DHT_sensor program.
If like me you want to use a DHT11 instead of a DHT22, change line 45:
DHT_TYPE = Adafruit_DHT.DHT22
into
DHT_TYPE = Adafruit_DHT.DHT11

and save the program on your raspberry

I saved it directly in my home/openhabian directory, i.e. the directory that is availble directly after logon

Now have a look at the usage instructions in the program (lines 36-42), but beware:
Presuming you saved the program as “mqtt.dht.sensor.py”, that is the name you need to use instead of “mqtt.channel.py” (the name mentioned in the “Usage”).
also.
I started my program as follows:

./mqtt.dhtsensor.py 'cupboard/temperature1' 'cupboard/humidity1' 4

This says that as my mqtt topics I have cupboard/temperature1 and cupboard/humidity1 and my DHT11 sensor is attached to GPIO pin 4 while the refresh rate is 300 seconds (the default).

To make it a bit easier I created a file called “dht.sh” that contained the single line:
./mqtt.dhtsensor.py 'cupboard/temperature1' 'cupboard/humidity1' 4 50
That does the same as the earlier line, but now I set the refresh rate to 50 seconds. I put it in one file because that is easier to type.
If you want you can make the dht.sh file to automatically start at boot as I describe below.

The MQTT messages are subsequently sent out over the network

And one could use definitions like below in your OpenHAB Items file to use them in OpenHAB

Number Cupboard_temp "Riser temperatuur [%.1f °C]" <temperature> (GF_Corridor) {mqtt="<[mosquitto:cupboard/temperature1:state:default]"}
Number Cupboard_humidity "Riser humidity [%.0f %%]" <line> (GF_Corridor) {mqtt="<[mosquitto:cupboard/humidity1:state:default]"}
Starting the script at boot

The script will run perfectly when started manually, but it will run in an instance of the SSH window and the moment you close that window, the script will stop. It is therefore better to have the script starting at boot. This is simple to do, but you have to be aware of the full PATH you are using.
Change the content of the dht.s file as follows:
Then in your preferred editor open the etc/rc.local file and add a line (the line at the red arrow):
Save the file and reboot. You will now no longer see the temperature and humidity in an ssh window, but the MQTT commands are being sent.

As this program sends its results by MQTT it can be used on other raspberry’s as well, noit just the one you have your openhabian and or MQTT broker installed on. Be sure though that if you install it on another raspberry, you alter the ‘servername’  variable into the name or ip address of the  MQTT broker

A word of warning:
If you are eager to test the program, before you  connected a sensor, it will just skip the sensor and you will get no useful feedback.
Furthermore, Python is quite sensitive to using the proper indentation in its programs as these have a meaning  in how the program is being interpreted, so if you go edit the program, be sure to keep the proper indentation

Added: Errors
If you install the above on an openhabian system you are unlikely to get any errors. However, I tested it on a freshly installed raspian Stretch system (not sure anymore if it was ‘Lite’) and I came upon the following Errors that were easy to fix:
Error
-bash: git: command not found
Solution
sudo apt-get install git
Error
File “setup.py”, line 5, in
from setuptools import setup, find_packages
ImportError: No module named setuptools
Solution
sudo apt-get install python-setuptools
Error
no module named requests
Solution
sudo pip install requests
Error
No pip
Solution
apt install python-pip #python 2
Error
Append error, logging in again: [Errno -2] Name or service not known
Solution
Most likely you are running the file from another raspbery where your MQTT server is not located. Make sure you alter the variable ‘servername’ in the mqtt.dhtsensor.py file into the servername or ip number where your mqtt broker is situated. Also make sure you do not have two clients running with the same name.

Error
“no module named Adafruit_DHT”
Solution
Go to the Adafruit_Python_DHT folder and do:
sudo python setup.py install --force

 

_________________________________

*) I could have used the mosquitto client that was on my raspberry that was already functioning as a broker, but as I also wanted to use it on other raspberries, it was better to use the lightweight paho.mqtt.client

A battery fed MQTT weatherstation

(Note: if you consider building this… I am working on a similar station with a bare ESP12 and a BME280 for even better energy efficiency)

Weatherstations are a popular build for DIY-ers and with the ESP8266 WiFi capabilities that has become very easy.
Here I will present a simple weatherstation (DHT sensor BMP sensor for temperature, humidity and atmospheric pressure) that can be battery fed or mains fed.
It will send the info by MQTT and in order to save batteries, go to sleep most of the time.
Components needed are:

  • A wemos mini D1
  • A DHT11 or DHT22
  • A BMP280
  • A 100k resistor for the battery
  • A small switch or jumper
  • A LithiumIon charger module

Just a word for the wise… the Wemos D1 is not the best option to battery feed, as it has some peripheral components (such as the CH340 chip) that draw current. A better choice would be the bare ESP8266, but it is not for everybody to solder that.

The application has OTA. Using OTA together with deep sleep is always a bit of a tricky situation as you cannot do OTA when the ESP8266 is in deep sleep.
basically there are 3 solutions for that:

  1. Include a pause in which you can do OTA. Problem with that is that you would need some indication of when that pause starts (e.g. once the MQTT messages have come in). Another problem is that that pause in which the processor is not in deep sleep, it wil consume more energy.
  2. Make the deepsleep dependent on the state of a pin. With a jumper or Switch you could make one pin high or low and thus allow deepsleep or not.
  3. By having the software check on a seperate website whether or not there is an update for the software and then download that software. Obviously that requires some more organization and if the Wemos will do that check whenever it awakes, it will do that say every 15 minutes for something that may never happen.

Considering the above, Option 2 seemed the best, so I added a small switch to tell the software whether or not to go into deepsleep.

Software

The program once loaded (get it here) has several tabs in the IDE.
The main program “esp8266_weatherstation” is quite straightforward, it sets up all the usual parameters, variables and the sensors.
It reads the sensors and sends these via MQTT to a broker.
Once that is done, it goes into deepsleep, depending on two parameters:

  • the “FORCE_DEEPSLEEP” variable: if present there will be a 15 min deepsleep. If not set, the deepsleep will be determined by the battery voltage.
  • the state of the ‘SLEEPPIN (D6):  if LOW there will be deepsleep, if HIGH, there will be no deepsleep

If there is no deepsleep, a pause of 30 secs is added to avoid the MQTT messages being send in a frenzy.

You may be puzzled by the following code section:

float h = dht.readHumidity();
float t = dht.readTemperature();
delay(2000);
float h = dht.readHumidity();
float t = dht.readTemperature();

The reason for this is the response time of the DHT22. If you  start a reading, the results you get are from a reading that was started 2 secs before. Usually that is not an issue, but if you put the processor to sleep for 15 minutes, that first reading will give you 15 min old values. If that is not a problem, by all means remove the delay and second reading. It will not make a difference on your battery life as your  DHT22 is not put to sleep.
technically ofcourse it is possible to feed the DHT22 from one of the I/O pins and switch it off when not needed, but the DHT22 also needs a warm-up time of about 2 secs, so you would need to take that into account. No doubt that warm up time could be catered for with the delay(2000) command mentioned above.

The “OTA” section sets up the OTA function. As explained before, OTA and DEEPSLEEP is a bit of an uneasy combination. In order to use OTA, tou would need to put the switch on D6 in the right position (HIGH) and either reset  the WEMOS or wait till the next wake up. Mind you that when DEEPSLEEPing the OTA port  can disappear, but it should come back once the processor is out of DEEPSLEEP.

the “config.h” file defines some variables

the “webconnect” file connects to WiFi. If for some reason that connection cannot be made after 10 times trying, the processor is going back to sleep for 30 more seconds and then tries again.

Libraries

The libaries used are quite standard, with the exception of the PubSubClient library. This is not the well known PubSubclient library from Nick O’Leary, but a fork made by Ian Tester. The reason for using that one is that it is easier to send variables in the MQTT payload.
The DHT library is the DHT sensor Library from Adafruit. If you prefer another DHT library (there are many) you will probably only need to make minor changes.
The BMP280 library is also from Adafruit.

The sensors

DHT22

The DHT22 is the more accurate sibling of the DHT11, but both have a tendency of failure. generally the DHT22 needs a pull up resistor, but one can also use the internal pullup of the I/O pin for that.

There are two specification where the DHT11 is better than the DHT22. That’s the sampling rate which for the DHT11 is 1Hz or one reading every second, while the DHT22 sampling rate is 0,5Hz or one reading every two seconds and also the DHT11 has smaller body size.

If you are using this sensor outside, you can protect it against dirt and  creepy crawlies by covering it with a single layer of teflon tape. Supposedly this is fully permeable for humidity.

The DHT sensors do not have eternal life. they give up working alltogether (and usually permanently) when the humidity is 100%

Properties DHT11 DHT22
Voltage 3-5 Volt 3-5 Volt
Operating current 2.5mA 2.5mA
Temperature range 0 t/m 50 ºC -40 t/m 80 ºC
Temperature accuracy ±2 ºC ±0,5 ºC
Humidity range 20-80% RH 20-95% RH
Humidity accuracy ±5% RH ±2-5% RH
Sampling rate 1Hz 0.5Hz
BMP280

The BMP280 is the successor of the BMP085, BMP 180 and BMP183

Ofcourse it is possible to use one of the above predecessors, but these older sensors are generally more expensive than the BMP280.
The BMP280 can measure barometric pressure with ±1 hPa absolute accuraccy, and temperature with ±1.0°C accuracy. It can be controlled both by SPI and I2C.

Do not mix it up with the BME280. That sensor can also read humidity, but it is slightly more expensive.
The BME280 ofcourse would be a perfect chip to go to if you want to avoid the DHT22 sensor. It can read temperature, humidity and barometric pressure. I just didnt have it lying around, thus couldnt try.

If you are no fan of the DHT11/22 consider the I2C HTU21D, or theSi7021 (replaced by the HTU21D).
If you are only interested in say temperature and not in humidity, the BPM280 is the best choice and you can omit the DHT22. If you only want temperature, the DS18B20 is probably the best choice.

The battery

Lipo Charge module

It is hard to give recommendations for what battery to use. I am using the battery shield to which I connect a LiPo battery. That makes it all very simple but it is not the most efficient way of using the energy from a battery as the battery shield first boosts it up to 5 Volt after which the Wemos makes 3V3 Volt from it.
Another easy way is to use a Lipo battery with a lowdrop 3V3 regulator and a cheap charging module (pictured top). You could combine the charging module with a small solar cell (with a 5-6 Volt max output). The 100k resistor in the  circuit sketch should go directly to the V+batt, to monitor the battery voltage. The choice for the 100k resistor is explained here.  If for power efficiency you decide to use a bare ESP8266 instead, one has the opportunity to increase the resistors of the voltage divider to come to a smaller current through these resistors

Dimming an AC lamp via MQTT

Years ago I published a TRIAC dimmer that could be controlled by a simple microcontroller such as an arduino. Times have changed and right now it is of more importance to be able to control that lamp from a home automation system such as OpenHab, Homematic or NodeRed.

So, let’s have a look at the circuit first:
This is a rather classic circuit. It detects the zerocrossing on the grid and then a microcontroller ignites the TRIAC with a time delay that determines the brightness of the attached Lamp.  The full cycle is 10mS (at 50Hz)
A circuit like this is easy to make for very low cost (1-2 Euro).

However, if you shy away from soldering  such a circuit, there are ready made modules available as well:
You should not need to pay more than 3-4 USD for such a module. Anything above that is robbery

Software to control this dimmer would look something like this:


#include <Ethernet.h>
#include <PubSubClient.h>
#include  <TimerOne.h>

#define CLIENT_ID       "Dimmer"
#define PUBLISH_DELAY   3000

String ip = "";
bool startsend = HIGH;
uint8_t mac[6] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x07};

volatile int i=0;               // Variable to use as a counter volatile as it is in an interrupt
volatile boolean zero_cross=0;  // Boolean to store a "switch" to tell us if we have crossed zero
int AC_pin1 = 4;// Output to Opto Triac
int dim1 = 0;// Dimming level (0-100)  0 = on, 100 = 0ff

int inc=1;          // counting up or down, 1=up, -1=down
int freqStep = 100; // make this 83 for 60Hz gridfrequency

EthernetClient ethClient;
PubSubClient mqttClient;
long previousMillis;

void zero_cross_detect() {    
  zero_cross = true;               // set the boolean to true to tell our dimming function that a zero cross has occured
  i=0;
  digitalWrite(AC_pin1, LOW);       // turn off TRIAC (and AC)
}                                 

// Turn on the TRIAC at the appropriate time
void dim_check() {                   
  if(zero_cross == true) {              
    if(i>=dim1) {                     
      digitalWrite(AC_pin1, HIGH); // turn on light       
      i=0;  // reset time step counter                         
      zero_cross = false; //reset zero cross detection
    } 
    else {
      i++; // increment time step counter                     
    }                                
  }                                  
} 

void setup() {
  
  attachInterrupt(0, zero_cross_detect, RISING);    // Attach an Interupt to Pin 2 (interupt 0) for Zero Cross Detection
  Timer1.initialize(freqStep);                      // Initialize TimerOne library for the freq we need
  Timer1.attachInterrupt(dim_check, freqStep);
  pinMode(4, OUTPUT);

  // setup serial communication

  Serial.begin(9600);
  while (!Serial) {};
  Serial.println(F("dimmer"));
  Serial.println();

  // setup ethernet communication using DHCP
  if (Ethernet.begin(mac) == 0) {
    Serial.println(F("Unable to configure Ethernet using DHCP"));
    for (;;);
  }

  Serial.println(F("Ethernet configured via DHCP"));
  Serial.print("IP address: ");
  Serial.println(Ethernet.localIP());
  Serial.println();

  ip = String (Ethernet.localIP()[0]);
  ip = ip + ".";
  ip = ip + String (Ethernet.localIP()[1]);
  ip = ip + ".";
  ip = ip + String (Ethernet.localIP()[2]);
  ip = ip + ".";
  ip = ip + String (Ethernet.localIP()[3]);
  //Serial.println(ip);

  // setup mqtt client
  mqttClient.setClient(ethClient);
  mqttClient.setServer( "192.168.1.103", 1883); // <= put here the address of YOUR MQTT server //Serial.println(F("MQTT client configured")); mqttClient.setCallback(callback); Serial.println(); Serial.println(F("Ready to send data")); previousMillis = millis(); mqttClient.publish("home/br/nb/ip", ip.c_str()); } void loop() { // it's time to send new data? if (millis() - previousMillis > PUBLISH_DELAY) {
  sendData();
  previousMillis = millis();

  }

  mqttClient.loop();
  Serial.print("dim1 in loop = ");
  Serial.println(dim1);
}

void sendData() {
  char msgBuffer[20];
  if (mqttClient.connect(CLIENT_ID)) {
    mqttClient.subscribe("home/br/sb");
    if (startsend) {
     
      mqttClient.publish("home/br/nb/ip", ip.c_str());
      startsend = LOW;
    }
  }
}

void callback(char* topic, byte* payload, unsigned int length) {
  char msgBuffer[20];
  
   payload[length] = '\0';            // terminate string with '0'
  String strPayload = String((char*)payload);  // convert to string
  Serial.print("strPayload =  ");
  Serial.println(strPayload); //can use this if using longer southbound topics
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");//MQTT_BROKER
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();
  Serial.println(payload[0]);

dim1=strPayload.toInt();

}

The value freqStep is usually set at 75 or 78 with this type of circuits, which allows for 128 steps of dimming at 50Hz gridfrequency. I have set the value here purposely to 100 allowing for only 100 steps, which is convenient for use in OpenHAB as  the slider goes from 0-100%.
The calculation is as follows:

50Hz
As we have two zerocrossings per sine wave, the frequency of zerocrossings is 100Hz. Therefore the period between two zerocrossings is 10mSec is 10000uS.
So if you want to have 100 levels of dimming the steps you need to take are 10000/100=100uS

60Hz
The frequency of zerocrossings is 120Hz, therefore the period between two zerocrossings is 8.3mS is 8300uS. So if you want to have 100 levels of dimming, the steps you need to take are 8300/100=83uS -> freqStep=83