@Reza I implemented your sketch, tried to start/stop(up to a few hours) the gateway(serial gateway) and the controller(domoticz on orangepi pc) to see if the logs help in some way. Nothing, it works.
It should be logged until the freeze occurs.

@Reza
there are two problems with MQ-2 sensors :
1 the sketch, at the bottom, uses log instead of log10
2 are you sure that RL_VALUE is 5 (kOhm) in your MQ-2 board? In my is 1, the one labeled 102 in the pic.

Regards

1 look at the last line of the sketch:

  return (pow(10, ( ((log(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}``

change to:

  return (pow(10, ( ((log10(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}``

2 RL_VALUE in your MQ2 board should be 1 (kohm), R2 in the schematic.

yes, R2 is 1k. Change RL_VALUE from 5 to 1.

I suggest you use the MQ-2 sensor library https://github.com/xerlay11/MQ-2-sensor-library and obviously change log and RL_VALUE.
Regards

Which MySensors library are you using?
With 2.0 i had the sleep issue solved (for now) with MY_PARENT_NODE_ID and MY_PARENT_NODE_IS_STATIC(as suggested by tekka).

@AWI Thanks for the hint.
I thought this wasn't a "issue" but just a "really annoying thing".
However i run domoticz on a Orange PI PC with WiringOP support and i can't find precompiled images.

It should be enough to read ppm from the sensor.

@jaykumar Yes,
i built it a couple of years ago, but it's operative for about three months.
I used :
arduino mini pro 3.3v/8Mhz powered by a 3.7v 14500 Li-Ion battery
NRF24L01
PZEM-004T (modified to work at 3.3v)

It's a simple watt/energy meter that sends data to the controller(domoticz) every 40 secs, the PZEM-004T does most of the work.

@Reza
sorry, I made a mistake. You have to check AOUT.

@Reza
you can't convert 16 bits unsigned integers greater than 32767 into 16 bits signed integers because they're treated as negative numbers according to 2's complement math.
You must check with a multimeter VCC(for supply voltage sanity) and DOUT( for ppm reading) on the sensor board.

I see two lines to be modified:

if (b == 0) { 
    uint16_t valMQ = MQGetGasPercentage(MQRead(MQ_SENSOR_ANALOG_PIN) / Ro, GAS_CO);


if (c == 0) {
  uint16_t valMQ = MQGetGasPercentage(MQRead(MQ_SENSOR_ANALOG_PIN) / Ro, GAS_CO);

@Reza
You are sending a 16 bits signed integer, so the maximum value is 32767.

send(msg.set((int16_t)ceil(valMQ)));

Try to send GAS_SMOKE instead of GAS_CO.
Pay attention to the power supply, the sensor need 5v 200mA ( i misured 130ma).

It should be enough to read ppm from the sensor.

yes, R2 is 1k. Change RL_VALUE from 5 to 1.

I suggest you use the MQ-2 sensor library https://github.com/xerlay11/MQ-2-sensor-library and obviously change log and RL_VALUE.
Regards

1 look at the last line of the sketch:

  return (pow(10, ( ((log(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}``

change to:

  return (pow(10, ( ((log10(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}``

2 RL_VALUE in your MQ2 board should be 1 (kohm), R2 in the schematic.

@Reza
there are two problems with MQ-2 sensors :
1 the sketch, at the bottom, uses log instead of log10
2 are you sure that RL_VALUE is 5 (kOhm) in your MQ-2 board? In my is 1, the one labeled 102 in the pic.

Regards

@Reza hi Reza,
LPGCurve[3]={2.3, 0.21, -0.47}; COCurve[3] and SmokeCurve[3] are taken from MQ-2 datasheet where 2.3=Lg200 but the sketch uses "log" in

int MQGetPercentage(float rs_ro_ratio, float *pcurve)
{
return (pow(10, ( ((log(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}

In my system log stands for ln=natural logarithm so i have to change log with log10 in the sketch and in the MQ2 library.
Try a Serial.print(log(10)) to check.

Regards

@AWI Thanks for the hint.
I thought this wasn't a "issue" but just a "really annoying thing".
However i run domoticz on a Orange PI PC with WiringOP support and i can't find precompiled images.