I have always wondered what the actual temperature difference is between the head and feet level of my sauna. I’ve also been considering to alter the ventilation to make this difference lower, but how would I know if I actually improve it? The answer is a dual level thermometer!
It is of course not enough to just show the temperature on two different levels, I also need to be able to follow it from my sofa while I wait for the sauna to heat up! To be able to do this, I added 2.4ghz connectivity through serial so I can build a second unit which is able to show the same information remotely.
For the logic I used Arduino Nanos as I had those lying around, and for the sensors I used the waterproof version of DS18B20 as that seemed to be the best fit for this. It is able to measure temperatures up to 125c so heat is not a problem either. For wireless connectivity I used a NRF24L01 Transceiver due to the massive range it has. I tried a simpler module I already had first, but the range was horrendous so I opted to order two new NRF24L01s to get the project done.
I still haven’t made the slave unit which will live next to the sofa in the living room, but for now I just log the temperatures every two seconds through a wireless serial connection on my computer. This way I can plot the heat curves later on, and also ensure that the thing works before investing more time on it.
For the enclosure I designed a simple model I can 3D print. It has a print in place transparent window on front of the screen so I don’t get any steam on it when the sauna door is open. The backplate also has brackets for the Arduino where you just click it in place.
Note from future me: Now the living room module is also ready – https://silfer.works/sauna-thermometer-living-room-module/