So, the problem is that at least one between your Raspberry PI Pico W and your Raspberry PI 4 model B isn’t connected to WiFi. The most probable is the RPI Pico. For this reason, please recheck your WiFi settings (SSID name and WiFi Password). Also check that your router hasn’t any kind of mac address filtering or blocking

No I can’t

Hi. Are you able to ping your RPI Pico W from the Raspberry PI 4?

I followed all the steps as you said, but I could not establish a connection between Pico W and Raspberry Pi 4. The publisher code in Pico W does not give any errors. I checked the passwords and IP address in the code many times. Also, when I type the command sudo systemctl status mosquitto.service, I see that it is active. Can you help me?

My – older – parents are used to use wood to heat their house but they are used to over heat the oven by throwing in too many or too big logs.
My idea is to give them a pico w with a display that shows them the temperature figures of the connected warm water pipes that run throught the oven, I mean the circulation of water temp. in and out of the oven into the heating system.

If the temperatures are quite high and close to each others it means that there is no demand for more heat or wood to burn like 60°C out and 59°C in.
If that would be a 50°C out figure and a 41°C in this would mean that a lot of heat is used in the rooms and it could be beneficial to add another log. They have reduced the oil consumption by 80% so far but I guess by overheating or over feeding the oven with too much wood.

My question would be like such of many others how to build a pico w temperature sensor (and if multiple can be used to show all room temperatures) and a pico w with OLED as a message / status display.
Beyond that how can that first temp. sensor transmitting Pico W be also used to transmitt further temp sensor data like for 2 at least in my case cause the pipes (in and out) are running so close to each other (10 cm) that it should be easy to glue such temp sensors to the pipes comming together in 1 pico W MQTT publisher.

I guess a lot would learn even more from such an example especially nowadays at least in europe where energy prices are sky rocketing and such a tool would help a lot to help people how to heat more efficiently cause above 60°C it does not make sense to throw in another log into the ofen cause only the exhaust gas temperature will increase.

And in this case my examples could be a great show case how to really benefit from that.
Just to let you know: I have already purchased a 2 sensor fridge temp sensor system with display. Works somehow cause the sensors are in a huge case powered by 2 aa batteries and far away from the pipe that the display shows far lower temperatures than the oven thermostats inside the pipes.

Final disadavantage of my “bought product” is the poor readible display, where the PicoW with OLED offers a better choice especially for older people that need bigger fonts to read them easily.
Yes, lot of points, but I guess that might fit pretty well to this first introduction as a real world use case cause everyone has a heating system and a pipe in / out temperature that might be usefull for a lot of people especially with mqtt and homeassistant / smarthome.

In case you have further questions or want some pictures of the current situation and the poor solution of the bought solution do not hesitate to write a mail. I will try to reply soon.

David, I just finished publishing an update on this tutorial with a section including the code to use the Raspberry PI Pico as MQTT subscriber, so reading messages from the broker. A feedback would be appreciated!

Hi David,
thank you for your feedback. Your question is becoming a common need. Or, said from a different perspective, many users need to get a backward MQTT communication from the MQTT server to the Raspberry PI Pico (publisher). Based on what I currently know, the Raspberry PI Pico can’t run an MQTT broker service but maybe it could work as subscriber… I’ll try to find something in this direction.

Hi Randa,
I suppose that the 2 boards can ping each other with no problems (a ping from RPI 3 to RPI Pico gives you enough info in a flat environment like a home one).
It seems to me a password issue. In some cases (I don’t know if this is your one), I suggest to avoid the minus char in password as when copied and pasted from MS Office it can give automatically the horizontal bar that has different value.
Please re-check it.
Moreover, please take a look at your “sudo systemctl status mosquitto.service”, that could give more info.
If we have no luck with these tests, you should enable the mosquitto broker logs on RPI 3 and check if there are some warnings or errors