sundberg84 Don't bother, I went through the hassle, downloaded Eagle and created readable PDF

@tbowmo Thank you, supercap idea works fine, my first experience with supercaps.

Sure, the curve is there. I am trying to make sense out of two points curve that is used in sketch for MQ2 sensor, CO gas. "point1: (lg200, 0.72), point2: (lg10000, 0.15)" while I see on the curve from datasheet (lg200, 5.2) and (lg10000, 1.3). That is why I am asking for help, sorry for not making it clear.

Lack of support makes you think, so I figured out the "hidden" calculations in the sketch above and proposing the code modification to allow users to port the code to a different gas sensor using data taken directly from the sensor chart. Here are modified fragments of the code showing only CO curve for MQ2 sensor:

float CO2Curve[4] = {0.8,200,2.2,10};
//two end points are taken from the curve with two coordinates for each point
//in form of{Y1, X1,Y2, X2) where X is PPM axis, Y is Rs/Ro axis from the sensor chart for specifc gas
//then equation X=(Y-b)/m is used,
//where m is slope of the curve, b is Y axis intersept point
float Slope = (log(pcurve(1)-log(pcurve(0))/(log(pcurve(3)-log(pcurve(2));
float Y_Intercept=log(pcurve(1)-Slope*log(pcurve(3);

int MQGetPercentage(float rs_ro_ratio, float *pcurve)
{
{ return (pow(10,((log(rs_ro_ratio)-Y_Intercept)/Slope))); }
}

@tbowmo Thank you, supercap idea works fine, my first experience with supercaps.

Does mySensors code have native WDT which would allow controller to see if node is ON or OFF?

@tbowmo Spamming network is a valid concern. I will look into super cap solution and send message or two when power goes ON then message when power goes OFF.
Also, I need to investigate how to let nodes communicate with each other without controller getting involved. Thank you.

@zboblamont Thanks again, amazing how human mind works, I came up with WDT solution while responding to your post...

@zboblamont Thank you, but I am trying to avoid powering node from dedicated power supply. I would like it to be powered by power source that goes on and off. One solution is to program it as WDT, generating pulses when it is powered up, so controller can detect condition when node is off.

I am looking for a simple solution to use one node as indicator that power is applied, so controller can detect status of this node. When power is OFF node is dead, when power is ON node is operational and its status is available to controller. Will appreciate any help.

Hello, I would like to better understand the concept here. It sounds like we still need a gateway connected to a controller (serial, Ethernet, WiFi, etc.) but the interface between gateway and multiple nodes is over wired RS485 serial interface. Please confirm. Thank you for your great efforts!

@zboblamont Thanks, you are proposing to filter out wrong reading, I am trying to understand why system periodically sends out 0.

zboblamont . Thank you, I understand all of this except I really don't see in sketch testing of two consecutive results in X attempts. I see that node will wake up and update the distance if new data is different than old data, but, anyway, question was about something different. Why, single sensor node based on this example periodically generates 0 distance? Are there different models of these sensors, so NewPing library needs to be altered?

Actually, even when I use this example without any changes with single sensor, quite often node sends out 0cm. Real distance in my office from table top to ceiling is about 160cm. Maximum distance set to 300.