MQ-2 smoke sensor MCU understands. ...

I happened to do it. The information I searched on the Internet is that MQ2 should have preheating circuit, then voltage divider circuit, then LM324 integrated operational amplifier for amplification, then AD converter for amplification, and then single chip microcomputer. Be careful that the heating resistance is not too small before preheating to avoid burning out the heating sensor. I'll burn one. The preheating current is too high. I made the object with reference to the following circuit diagram, but it has not been verified yet, because almost all MQ2 data did not give him the resistance value in the air. Last night, I measured 1.2M, and it felt too big. I'm also worried now. Because MQ2 has different conductivity at different PPM of different gases, you should estimate the alarm resistance according to which gas you want to detect, so as to choose the voltage divider reasonably, and also consider how much voltage AD can convert. I chose ADC0809, which can't exceed 5V at most. It's really troublesome. It would be nice if merchants could integrate AD into smoke sensors like DS 18B20. Also, you can choose a single chip microcomputer with internal integration of AD. This is just a reference, you should design the circuit reasonably according to your own needs. The above is for reference only. ...