Not so much a MySensors build as an example of how even the most basic information can inform changes for the better, in this case space heating.

The system here is fairly basic, an array of DS18B20s, some ultrasonic tank probes and a gas reed sensor, temperature is updated every 5 minutes, the gas updates every 0.05m3...
With winters here down to -20, the first priority last year was insulation, and even though a modern house, the gas bills essentially halved over the year, effectively funding not only the insulation, but replacement axial radiator valves and thermostat heads (Heimeier) to replace the typical arrangement of unknown origin, with spare... But now the MySensors impact..
This autumn's attention turned to the central heating unit, a modern combi unit of good manufacture, installed by a 'certified' heating engineer, but aside what little I knew about condensation boilers and the steep learning curve that followed, I was bemused by the return from the radiator loop almost burning my finger within 10 minutes of the system being fired up. This did not make sense for what I understood of a condensing boilers, which compelled a look inside for the first time, the manual and some googling.

The boiler is a 25kW combi with minimum output 7.6kW, the radiators account for ca 13kW at Delta 60 set for 15c drop (previously set ca 20c drop), settings since day one were 65c and the pump was set at max output of 3, last year's -20 resulted in 13.5m3/day gas consumed, not crazy by historical records, but hmmm.
So now comes tinkering with data from MySensors via Domoticz to inform...
Currently the boiler is set at 55c, the pump is on Low (40 v 84w), but the results are surprising - Slower rising temperature when ON, 42 minutes v 25, but gas use dropped from 0.75 to 0.6m3, but here's the kicker from that longer heating time, not only less energy used per cycle, but longer and thereby fewer cycles per day. Current evaluations are between 15 and 20% savings, so thank you to all the MySensors community and contributors..

Surprised I'm not bald will all the hair pulling and failed attempts to get there but after a year it is finally working...
The task was simple enough, to measure fluid depth in two tanks, one a sewage holding tank, the other a bulk water tank. Just figuring out which method worked with which board was an exercise in frustration, but the JSN-SR04-2.0 turned out the only one of the two I could get to reliably work.

Despite the industrial look, these waterproof light switch enclosures proved ideal, as the batteries in holders fitted beneath the clear plastic. A little hacking out of the switch 'fingers' with a Dremel gives plenty of space in the base area.
Battery holders are held in plastic conduit which are hot glued to the back of the box poking through the front section aperture.

The top case is a 3v3 WhisperNode with onboard RTC and RFM69, and tucked under the spaghetti in the top left back corner is a level converter. The RTC wakens the Node every hour to initiate readings, and despite a few hiccups seems to be reliable. The WhisperNode is allegedly capable of draining the 2 AA cells down to 0.9v, time will tell...

The lower box holds the 5v ProMini, a small latching relay, and the ultrasonic board, the button type ultrasonic (like parking sensor) is mounted on the end of a 3/4" collar to 1/2" galvanised steel tube drilled centrally through the roof of the 1.34m x 1.67m tank area.

Connection between the cases is via Cat5e in 16mm conduit, 2 cores for I2C, 3 cores for relay control and 3.3v power, 2 cores for 5v and ground to the level converter.

Despite worries over echoes in the resulting space, the tank was emptied last night, and the reading is coming in with the occasional glitch at 1620mm depth from the head, which I believe has a cone angle of 45 degrees.
The Node control of a Relay by On/Off pins to Mosfets may seem wasteful, but I had them anyway. The 5ms on/off of this small latching signal relay boots up the ProMini and seems reliable.
Still to incorporate a WDT/Reset on the 5v as it periodically hangs, and a time limiter on the Node to complete the task, but glad it is all all working semi-reliably, even if some of the programming side I still don't understand...
The 5v tests for 2 consecutive identical readings, the 3.3v tests that it fits within acceptable range, and if not calls for a further reading.

Once delivery of a second identical board from China is done, the water tank should be a lot easier. This one is the more important, as ran out of water previously due to corrosion of the level probes in the tank (3 core cable and short bolts) which stopped the borehole pump topping up the tank, and the hidrofor hit it's cut-off electrode. The level monitoring will give early warning to go investigate long before the bulk tank is 'empty'...

Postscript 12/7/18 - Water tank worked flawlessly from first deployment, but led to concerns over dropping battery voltage.. The problem appeared to lie with the Master sinking power through the I2C lines, but a routine to null the SDA/SCL lines prior to sleeping seems to have halted the decay.
One of the unexpected results of the Sewage Tank deployment was detecting a dramatic rise in level during a heavy storm (85mm in 24 hours) initially thought to be ground water intrusion.
Excavation to the incoming pipe connection to the tank found a round pipe in a square hole (not exactly an unexpected building practice here, now packed out and sealed.
Losing 30% of storage capacity would otherwise never have been detected, so it the deployment has already paid for itself handsomely...

@pepson This reminds of that famous quotation "Any ship can be a Minesweeper..."
"Once...."

@neverdie Would this work ?

@sundberg84 Yeah, this brings back memories, particularly of quite a few hangovers.
I used 3 and four wide fireclay pipes for bottle storage, they were used for ducts back in the day before plastics took over, cable went optic fibre. I noticed recently here they are back in stock in stores as....yep...wine storage racks.... but wacko pricing relatively...
The beauty of the fireclay was it's slow temperature and humidity change, and this formed the bulk of the thermal mass in the cellar I made below the floor.
I used a 150mm glazed ceramic drainage pipe dug in under the garden as a loop (rope caulked joints - anybody remember them), from memory down about 1.5m, both avoiding frosts and baking sun, don't think the temperature varied over a degree all year round, the ground acting as a massive heatsink which maintained a constant temperature all year round.
Only when the hatch was opened did the temperature jump, a small fan kicked in when the hatch was closed and ran for 30 minutes, a second contact switched on the lights and shut them off, long before LEDs were so prevalent, old reliable (until you were depending on them) incandescent bulbs.
That was it really.
Biggest problem I found was humidity in the early days, probably the fresh construction...

@tbowmo Hah, you were lucky, I finally upgraded from the monochrome to colour...

@sundberg84 Easy, one is disconnected... At 90 degrees?

Finally the round-tuit UPS got built after the last power cut clobbered the Controller/Gateway system, lesson learned...
Meanwell AD-55A, 7.2Ah Acid gel battery, two usb 5v buck converters, a spare socket for raw volts, and a 15 euro IP66 box from the local shops.. Some drilling and filing to the lid, couple of brackets, spare bolts, banding, soldering and hot glue...
A bit bulky, but disappears in a void under the stairs, two tiny drill holes let the buck converter leds shine threw...
No monitoring as yet, but sailed through a power cut this morning and the Pi didn't skip a beat.. First up is the Pi's RTC then can put the cover back on the Controller...

First of the winter projects done, just the programming to finish and replacement temperature chips to get (broke the legs off both DS18B20s through clumsiness).
With mains/battery backup and RTC, it will record boiler start/stop and run times as well as feed/return temperatures, and as an aside the inevitable power cuts which plague this part of the world.
The MCU plugs into a socketed backplane hot-glued to the back of the box should removal prove necessary, but quite pleased it is sturdy and all fitted into a slim 25mm deep standard (cheap) box.

@NeverDie Was "starting to warm-up" an example of Texan humour, or accidental, given how this thread started off....?

@mfalkvidd May I suggest a new pinned post in Hardware and a link to your new section may make make life easier for those starting, effectively expanding this thread to collate opinions and experiences?
A table with type, shelf life, self-discharge rate, voltage, etc. may be later drawn together with experience from others here with LiFePo etc. and pros/cons found, and with ever changing technology, expandable ?

In addition to the above, as @Yveaux pointed out the processor can be run almost to battery death, so only the voltage requirements for the sensors may limit your options to running at 8MHz.
My Nodes were bought as a specific variant with onboard booster, so it is technically possible to build a highly efficient booster, but it's unlikely to come from China's mass market.

But this then touches on the point made by @mfalkvidd, rechargeables have very different characteristics to alkalines (Google for info on battery comparisons performed by others). I went through this extensively before starting up, and no regrets on alkalines.

As @Nca78 referred it also depends on load and duration.
My faster processor executes the radio update on a gas reed trigger then goes back to sleep within ms with no external load, 2 years later the Node batteries read 2v.
The tank monitor fires a 3v ultrasonic routine at 8mA every hour and maintains an RTC, but aside hourly routines is in deep sleep the vast majority of the time. 6 months in and Node batteries are at 2.89v, so over a year is guaranteed... However, without it's onboard booster it is likely the ultrasonic would have stopped working.

A further option to where a sensor needs a higher voltage is to switch on a secondary supply specifically for that sensor. I didn't have much joy with that using a booster due to noise, but it worked fine with a battery pack and VR.
Hope this helps...

@Joe Perhaps have a closer look at the failed supply you will probably find a model number (possibly under an Ikea label) which happens to be a a stock Mean-well supply, Ikea don't make PSUs...

@NeverDie I don't mind it so much as an overview, it's getting sense of the overview which is the problem as the detail is absent from the graphing.
Simple enough for my purposes though, sitting in a kitchen with a glass of Rioja recording details is remarkably simpler than spilling a perfectly good wine dashing back and forth balancing a notebook, pen, laser thermometer and a clock..
We work with the tools we have, which on balance are a lot more advanced than when I was your age when flints, candles and acetylene were all the rage...

Not so much a build as a case study in deploying Mysensors with Domoticz to solve a puzzle simply with heating.
Having retrofitted insulation 2 years ago to my relatively modern house (2013), seeing gas consumption plummet to 55% of previously was a joy. The unknown thermostatic valves and heads were replaced with Heimeier Eclipse and Halo devices a year ago and an undersized Lounge radiator replaced (all paid for out of the first year's savings). The original intent of electronic zone control was abandoned when prices rocketed since the original goal was it being self-funded by first year savings, so a Honeywell multi$ was nowhere on the cards in any instance.
As Honeywell and other modern valve manufacturers have manufactured for thermostatic control, the Eclipse is essentially a dual flow control valve, one part replicating the return or lockshield valve (which is left fully open), the other the thermostatic control. On paper the Eclipse offered the secondary advantage of being pressure agnostic per kW panel, you set the flow and it stays that way.

Delighted though I was to break 50% savings over the original thereafter with rooms remaining within a 1.1c band, there were some rooms colder than were set which made me realise there was some imbalance which I didn't realise then was the transit time from boiler to radiator (or miscalibrated valves).

First step was smart in but stupid out, monitoring the boiler by attaching DS18B20s to the connection nuts. Outgoing measured temperature being 10c below the boiler setpoint should have given a clue, but a week of running round like a lunatic with a laser thermometer and a notebook proved I was none the wiser other than the radiator was hotter than the boiler sensor.
Hence deployed this, a temporary hookup of two DS18B20s on perfboard connected with Cat 5e and phone cable and held with hot glue, two G clamps and some cardboard to ensure they stayed put, and a roving Node...

Not elegant but dysfunctional (hot glue struggled under heat and pressure including having to be levered off the radiator) but it enabled the problem to be identified, transit time... Being able to monitor both the top and bottom panel temperature in relation to the main rads helped nudge the time to get incoming temp close to that taken to hit the main rads +/- 1 minute within a cycle time of 18 minutes...
Not elegant, and Domoticz is useless being built around 5 minute intervals, but it still enables readings to be taken with a notebook and pen in one hand with a glass of Rioja in the other Creeping up on it.. The improvements are felt before they are observed.
My point is, a temporary Node can serve a lot of useful purposes leading up to or supplementing the permanent structure.
The screenshot is two different targets being tweaked...

@j54n1n If not, would a second low power non-radio board handling the two Ints (and any other expansion) be a viable option ?

@neverdie Good man, and wonderfully timed...
I've only just realised it's potential solution for an application here...
Have volt-free NOs on two pump contactors, one held closed other than in power failure, the other only closed when the borehole pump is called...

@j54n1n Just skimmed this so pardon me if I misunderstood through the hangover....
If I recall correctly there is a method of using multiple triggers to a common Interrupt pin someone tested here presumably involving diodes and resistors but crucially linked to ADC input. On wakening from interrupt the first task was identify the culprit... If I remember rightly @NeverDie extended the principle using a resistor array...
Hope this helps while I'm researching the wonders of aspirin...

@sundberg84 Out of curiosity, did you have battery powered Nodes trying to contact a dead controller or did you shut them all down?

When the Controller here died in June/July, the hit on Node voltage was quite spectacular compared to normal decay, in this instance the gas meter which was only supplying hot water and cooking...

@pihome I wouldn't hold much store by claimed/calculated gain, it is a minefield... eg the 110mm whips referred to earlier are commonly referred to as 2dBi, quite a bit shorter than the theoretical 170mm quarter wave.... But crucially, they work flawlessly, on standard power modules, to 50+m, through structures.... Have not yet tested one in the below ground pump chamber, but would not be surprised if it worked.

Although tempted to play with the auto-power facility on the RFMs when it was made available on the newer driver version, since the reduced erp would have limited impact on battery life, didn't pursue it.
I would suggest seeking to increase power to overcome receive limitations MAY lift the signal out of the mush, but would not make for stable comms..
Others here are better able to advise, but I vaguely recall a portable RSSI test setup having been outlined. So going back to a question from my first post, perhaps a couple of pro-minis so set up with differnent antennae would yield clues toward a solution.