So after some considerable time and loss of sanity I now appear to have a stable setup. I'd like to share what I have done in the hope it may save others a lot of time and frustration.

By enabling debug in the sketches, I eventually realised that I could not get any node to communicate reliably with the gateway. I was getting lots of NACKS even at short distances.

I was sure that the problems were radio related but after trying many NRF24 modules I was about to give up.

Then I read a post somewhere about ground planes.

As a last resort I added a piece of aluminium between my gateway antenna and the radio. (PA/LNA Version). Eureka!! This has pretty much solved the NACK issues.

Following this one or two nodes still intermittently lost contact after a few hours or days. What is strange is that even if moved close to the gateway, errors continue until the gateway is power cycled? I still don't know why this is.

I solved this problem by converting the Node PCB antennas into a dipole antenna as detailed at https://www.instructables.com/id/Enhanced-NRF24L01/.
Now all nodes stay connected.
Now after a couple more weeks of testing all is still good.

I am using Domoticz with the MQTT output passed onto Node Red and now have some really cool things going on.

A big thanks to all that replied and pointed me in the right direction.

@reindier I discovered mysensors while also looking if it was possible to build my own alarm system.
I am pleased to report that it is quite possible if you don't mind the fun of building and fault finding.
I started a few months ago by building some PIR sensors and a serial gateway on a raspberry pi running Domoticz.
From there on I'm slowly adding to the system. I now have notifications for doorbell, outside temperature, solar panel voltage, sensor battery voltages, Sonoff light running Tasmota..... just this week I've swapped over to an ethernet gateway.

All the information is available if you take the time to browse the site. Lots of help on the forum as well.

@skywatch Appreciate the reply. I have made up some 500mA quick blow fuses that I already have from a trusted source.

I have found a workaround by sending the heartbeat message as a separate V_MULTIMETER child. This then gives me a voltage reading of 0V every 30 seconds that I can use with the Domoticz last update feature

Would like to hear any better ways of doing this.

Thanks Omemanti

I will check out myscontroller...looks useful.
Ive been playing with openHAB today, and after a bit of a struggle, I've managed to create a virtual switch that sends me an email. This gives me hope that a mysensors PIR node will be able to do the same.
Certainly a great way to learn about many new things!

Here's a quick vid of this morning's project. Getting Alexa to speak the values from the node in my garden.
Alexa speaks arduino mysensors readings – 00:25
— grumpy oldgit

Credit goes to those who made the node red nodes to make it work!

Thanks to all your replies I think I've got it fixed.

I tried another pro mini....still eratic.
I then used that second pro mini and built an identical node on another breadboard. Result was perfect readings.
I then rewired the problematic one and gave it another battery for good measure. It is now more than acceptable although still not as smooth a graph as the second node.
At the moment, running direct from 18650 and not boosting to 5V does not seem to be an issue for the HC-SR501's.
Maybe I will run into problems as the battery voltage lowers.
Node2

Node1

@guillermo-schimmel I have had a look at openHAB but it took me half a day to work out how to get it to send an email. Domoticz seems somewhat easier for a beginner like me. I also like the way it has user accounts built in.

I must say I like the idea of communication with a vacuum cleaner. Maybe I need to get that dust sensor ordered?

@mfalkvidd Thanks for that clarification. I am also thinking of swapping from serial to ethernet when I have time so I can use MQTT.

@mfalkvidd Sounds reasonable. I am thinking a small UPS would be a good idea so I could keep my raspberry pi's, router, switch etc going as well.
Time to look at that relay node then!

Thanks for confirming this.
I will have to be careful when swapping code for testing purposes. I restored the Domoticz database and all seems back to how it was.
I will probably create another post for the actual issue I am having with the node....will try and figure it out myself first. something not right with my code as about 15 unknown childs have been created and the node has high power consumption, like it is restarting constantly. I have ruled out hardware.

I have a problematic sensor running PIR/Voltage/Temp/Hum

I uploaded some different code (PIR/Voltage Only) to test but it messed up the childs in Domoticz so I deleted them
Now when I restart the node they do not get re-recognized.

I know that deleting the entire node causes Domoticz to forget it forever. Is this the same with child objects?
I will restore from backup for now.

@Yveaux Makes sense now. Thanks again.

@Yveaux

Thanks for that explanation. Understanding this, the bit I am still confused about is how I can use wait() and still able to listen for incoming messages. Is that an exception to the rule? What stops the processing being blocked in this case?

Hope ok to ask here as I am struggling a bit to understand wait() in context with loops. I have used it with success with a separate receive function but need a bit of clarification.

I have read on another post that wait is the same as using the millis method but can't get my head around how to use it.
If using millis I would use the state machine if else method as suggested by @scalz

How do I use wait in one place and then get another loop or process to run in the meantime?

I have watched the video and tried to follow along. here
My test board is a pro mini 3.3V 8Mhz
I can read the fuses with AVRDUDESS and I get
L FF
H DA
E FD

This does not seem to match with the recommended settings but there is no mention what to do on the video?
The text suggests burn other values.
I am guessing I have an external oscillator as I can see the crystal on the PCB? The instructions don't show settings for 8MHz external.

Next I have copied over the necessary boards.txt information, but there are 2 options for 8MHZ. MYBL8 and MYSBLNRF.
Both show up in the arduino IDE as 8MHz RC in the boards/frequency section.
I dont't know which one to choose.

Also if I want to to use a channel greater than 110, I need to compile the hex file.
Is there a guide on how this is done. I have searched but drawn a blank.

Any guidance appreciated.

@trond-arntzen I just use a voltage divider with 1Megaohm and around 82K resistor for measuring my solar charged battery.

@Mustang65 That ups board looks good. I could do with something similar as a battery backup for my raspberry pi's. Of course they would need a 12V to 5V conversion.

@mfalkvidd said in Sample sketch for test node including hardware and software acknowledgement:

char messagestring[100];
message.getString(messagestring);
Serial.println(messagestring);

@mfalkvidd Fantasic. Thank you. That is what I was looking for . It works now !!!

@BearWithBeard Thanks for confirming this. I had tried most of the options listed on the MyMessage page.

I have tried both ways you suggest again just now - getString() returns nothing and getUInt always returns zero.
At the moment it does not matter as I can see the value listed at the end of the echo(as posted previously) it would just be nice to be able to "harvest" it.
For now I will use the value that has just been sent - for resends etc.

@Yveaux Thanks for the link.
I'm not sure if I am missing something simple?

So I can see the echo in the monitor :

173 TSF:MSG:READ,0-0-9,s=1,c=1,t=16,pt=2,l=2,sg=0:111
182 TSF:MSG:ECHO

In this case the original sent value was 111 and I can see it in the echo message.

If I do

Serial.println(message.isEcho());

I get a 1 printed. Is there a message.something that contains the original sent value?