@Boots33 I haven't done a writeup of mine, perhaps I should fish it out of the pool sometime and get some photos.

The DS18B20 has a tiny standby current, something like 750nA. Even with 30 second poll intervals, I'm finding my sensors typically get near-shelf life from the batteries.

The physical setup is pretty basic - just a Pro Mini, battery, radio, and ds18b20. There's no circuitry for regulators, dc convertors or battery sensing. Of course I did remove the onboard regulator as it will draw power from the 'out' pin.

One thing I had to do was reprogram the fuses - you may find the Pro Mini comes with the BoD fuses set to like 2.7v. You can set it down to 1.8v so you'll get much longer life out of it. The effort is worth avoiding the hassle of more frequent battery changes.

Battery level sensing uses this VCC library: https://github.com/Yveaux/Arduino_Vcc

Nice project! I did one also with the same original thermometer. A couple of differences with mine:

• I used a DS18B20 which can run at a much lower voltage, so my batteries can get to about 2.0v before problems happen.
• No boost converter, everything runs straight of 2 batteries so the part count is less as well as avoiding losses in the converter.
• Battery voltage measurement is via the Vcc library which uses no external connections to the arduino, but is accurate enough for this use case.

In the past 5 months my battery voltage has stayed at around 2.97v.

For those looking to 3d print a case for this, if you cant find the right sized ducting, I designed one thats unobtrusive:

https://www.thingiverse.com/thing:2418194

All of the ducting near me is a bit too slim to fit sensors based on this, so I decided to design and print a case instead.

Does the trick nicely, and I also chose to use proper AA battery clips to retain a good connection, as the cable-tie battery assembly wasn't holding well for me!

On the Thingiverse page I have a link to the original OnShape doc.

https://www.thingiverse.com/thing:2418194

Thoughts, suggestions, etc will be much appreciated!