It’s interesting because I know others have done this to measure water levels, but when I searched, I found only 2 people having reported “functional/semi-full” solutions. One guy who did something very similar to me with PVC for the build/mounting + an arduino (if I remember, this was the hack-a-day thing – I also think he ran the sensor to the tank, and everything else was external w/ cat5), and another person who used the cheap ESP8266 but to measure water level in a fish tank. Obviously the concept is the same, but I didn’t really find much around oil – especially the tank measurements encoded (as data/table/function/etc).
To your point - yes, you can get an esp for ~$4-5, but usually from china and then you wait+shipping costs. If you get a ton of them in bulk, it gets closer to $3-4 delivered. I know you can get something like this for $8-9: https://www.amazon.com/HiLetgo-Internet-Development-Wireless-Micropython/dp/B010O1G1ES/ref=sr_1_3, but then you have to deal with everything from wifi connectivity, tethered firmware updates, and writing all of your own REST notifications, variable publishing/retrieval/etc. It’s just too much of a pain for saving $8-10.
For me at least, the Photon is well worth the 40-60% cost purely for the remote API/remote updates/ease of interacting with remote points/REST/etc. If that was not available, I would probably go for the HiLetgo which seems in between the Photon and some of the more “raw” esp8266 (from banggood, ebay, etc)
Anyway, the concept (or code) is not really unique. I was just hoping to achieve 2 things with the project/post:
1.) provide a cheap way for someone to build an attachment for their oil tank (PVC build) which is semi elegant and compcast
2.) provide all of the code so that someone could just copy and paste it and start getting notifications about their oil levels without having to worry about any specifics.
It pained me to see companies charging hundreds of dollars for the hardware solution + a monthly fee (when over ethernet) for the “data/notification service”.