ESPHOME + MQ4 Help

ESPHome
1

Hi I wanted to know if it is possible to use the MQ4 sensor in the same way as the MQ2, and (if so), if the formula reported by OttoWinter “((5.0-x) / x) / 9.8” was fine for this sensor too. Thank you

1 Like
2

In principle there is no reason why it won’t work, but you’ll have to consult the mq4 datasheet to work out the formula.

3

They are pretty similar but still have some important differences in sensing so you’ll need to do some adjustments according at datasheet of each one !
Datasheets avalaible on that page if needed :wink: https://www.mysensors.org/build/gas

4

Hi, looking forward to your work.

5

This is an old thread but have you managed to to have MQ4 in ESPHome and if so can you share the config? Many thanks!

6

the PPM formula for MQ4 could be picked up from https://www.teachmemicro.com/mq-4-methane-gas-sensor-arduino/
if anyone was able to get this working in ESPHome please share your thoughts! :slight_smile:

7

Hey Adrian,
Were you able to figure in out in the meantime? I also have a MQ4 connected to an ESP32, and I get the voltage. And now with just some simple math I can convert into PPM CH4. But in yaml the sensor block I cannot get the log and the raising to the power of 10 done. Do you know how to do that?
– Paul

8

Hi Paul,
In Home assistant you just get a value… I just made a rule if is over 40 then it detect gas so it turns off the gas at meter + notification… It works but I had some false positives …
If you have figured out the math maybe you can share the formula and we can do a template sensor in HA rather than in ESPhome…

Regards,
Adrian

9

Hi Adrian,
I’ll give it a spin. I’ll let you know if I succeeded.

– Paul

10

Hi Adrian,

I did a bit of math. The difficulty is that the scales are both log. So you need to determine the slope of the line in the log/log scale. If you work it out you can program it as follows:

  - platform: adc
    pin: GPIO36
    name: "MQ4 CH4 sensor"
    accuracy_decimals: 0
    id: MQ4_CH4
    update_interval: 30s
    filters: 
     - lambda: return (pow(10, log10((0.12/x)*(5-x)/(5-0.12))/(-0.35))) ;
    unit_of_measurement: "ppm"

But is all fairness, your suggestion of having a limit works out to do the same. Just that in this case you get an approximate PPM number.

– Paul