One of these basically
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> The tank already had a hole in the top to take an oil watchman sensor,
> so I 3d printed a case to use the same mounting holes and gasket. I will
> need to open up the hole a bit for the ultrasonics
Ours is a steel tank, but it has a tube poking out of the top that has previously accommodated a Watchman sensor.
Housing the electronics is the problem - I had hoped that oil tank sellers would sell a screw-in cap for the tank opening that I could cannibalize to make an appliance housing, but I haven't found anything suitable (yet).
I really needed an excuse to get into 3D printing. :-)
Well since I am 100% custom I didn't bother with mqtt - I simply send a short text string . The more problematical bit is establishing a wifi connection and what to do if it fails to connect.
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> If I had Ethernet out there I would never have gone to the complexity of battery operation....
I used MQTT because I already had Mosquitto running on the Pi3B (as part of a HomeAssistant setup controlling a few Tasmoto switches). I should not have gone that route otherwise ... but it does work well.
Yes, if I had Ethernet running out to the tank it would all be so different ... but I'm not drilling a hole through a 60cm stone wall to get it there!
> I have a 3V-compatible HCSR04 to play with ...[snip]
> Good with the 3v version Mine isn't and I expect it to get sketchy at around 3.9V.
> If that proves to be a problem I'll probab;y make a new board up and transfer the modules from the existing...
Mine is actually an RCWL-1601, which claims HC-SR04 compatibility. It also claims to support i2c as well as the usual trig/echo signalling, which will help as me ESP8266 is running out of pins. I may have to switch to an ESP32 ... but I have a handful of 8266s not doing a lot ...
I don't like the commercial solutions that rely on a cloud somewhere.
No, indeed. I avoid those as much as possible.