this is the same as Problema obteniendo datos de Sensor MQ135
Cross-posting is against the Arduino forum rules. The reason is that duplicate posts can waste the time of the people trying to help. Someone might spend a lot of time investigating and writing a detailed answer on one topic, without knowing that someone else already did the same in the other topic.
Please create one topic only for your question and choose the forum category carefully. If you have multiple questions about the same project then please ask your questions in the one topic as the answers to one question provide useful context for the others, and also you won’t have to keep explaining your project repeatedly.
Repeated duplicate posting could result in a temporary or permanent ban from the forum.
Could you take a few moments to Learn How To Use The Forum. It will help you get the best out of the forum in the future.
Thank you.
➜ Take note that you should use English if you post in the general forum, you can use Spanish in the Spanish speaking categories which is where I moved your post (and closed it for the time being)