Hello,
I’m trying to use a MQ-7 sensors on ESP-12 to detect carbone monoxide.
I saw i technical specs that I have to heat at 1,4v and 5v alternatively. I have some difficulties to wire everything. Does some of you have already use this sensors ?
Thanks.
Have you had a look at this …
it might help 
Yes I’ve tried it, but this works with an Arduino with PWM and 2 to analog input. I want to replace Arduino by an ESP8266 node MCU to get Wifi + MQTT.
I can use only one Analog input to read MQ7, A0 is OK.
But how can I switch between 1.4v and 5v without PWM ? I suppose I can use a transistor or mosfet + 2 resistors to make a 1.4v. But i have not enough knowledge in electronic to find the solution.
If a different hardware solution was a possibility - how about this, it uses MQTT, with a Pi Zero maybe?
I just got mine in the post, and it’s a great sensor - very fast readings too.
So a quick search gives …
from …
https://iot-playground.com/blog/2-uncategorised/53-esp8266-wifi-gas-sensor-arduino-ide
Enjoy
This seems to be for other MQ sensors working on 5v. The MQ7 is a bit different, because it need to be heat a 1.4v to read and 5v to heat. In this example the MQ is always 5v 
Yep my mistake, however I found another that uses a relay
