What can you measure with uni as battery monitor? Can you measure charging and solar input voltage
I wish there was an inexpensive DIY technology to monitor the level of a flexible tank… The clear water tank on my boat is flexible coated kevlar. It’s nice because it fits into a hard to reach compartment. The problem is that it fits into a hard to reach compartment 
So trying to get the level manually is a real pain and usually involves poking it with a stick to feel how flexible it is. Best would probably be to install a flow meter and some form of reset when I fill it up. But I would probably forget to reset it after a refill.
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It will measure whatever voltage you connect it to, so in my case, it typically shows an output somewhere between 12-13V on my 12V auxiliary battery. I have not put one inline between a charger and my battery, but I don’t see why you couldn’t.
Didn’t want to report back, before I got some reasonable time to see if all works as expected… 
What can I say, I forgot about it, because everything works as expected. 
I did install it in my engine compartment, right next to my fuse box. I also printed a small case, put some cable ties around it and last but not least I used half a roll of insulation tape. That’s it.
My car is parked in front of the building and the WIFI signal reaches easily (3 out of 5) to my Pi in the garage (around ten meters, but an aluminum garage door). So far, so good.
I have just one little thing, I’d love to see: integration in ESPHome, but that’s really not a deal breaker. Right now it works with MQTT and the Shelly UI.
Oh, and I forgot to tell. The first setup, better the correct calibration is a bit try and error, but all in all it took me less than an hour to install and setup.
I can say, for my use case, it seems really like the perfect device. I can’t say much about the long run, still different stages of lockdown here, so I hadn’t had the chance to give it a long run on the Autobahn (highway), but tbh I don’t think there will be any problems.
I can def. recommend it.
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I guess it depends on what you want to monitor. Voltage, sure. But really at some point you want state-of-charge (SOC.) For that you’d need a shunt. There are off-the-shelf solutions for this, so I’m not sure how much there is to be gained by rolling your own.
Load cells? Possibly several with a small custom fiberglass frame to go under where the bulk of the water pools. Like a bed occupancy sensor.
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I thought of that. The problem is that due to the boat moving constantly when sailing and even when moored, the waters’ center of mass will shift around randomly and the tank deform. So the weight measured by the load cell will very unreliable. You’d pretty much have to line the entire tank compartment with hundreds of small load cells, gyros measuring the boat orientation in 3D space relative to gravity and then use a high power CPU or GPU to run a realtime fluid dynamic model in order to estimate the amount of water bouncing around in the tank 
Sounds fun, but I think the poking-with-stick method is probably going to win in terms of complexity and power use
Edit: thinking of it, using a couple of load cells at the bottom could perhaps be enough for a very rough averaged estimate of the tank contents (maybe displayed on a n/5 scale) when in calm waters or moored. Which would already be nice. Might try that out.
I don’t own a boot (unfortunately 
), so please bear with me, if this is a dump idea.
I’d try to measure the outgoing pressure. I’m assuming there is one “out” line at the bottom of the tank, and this is, where pressure should be readable. The higher the pressure in that outgoing line, the more water (or whatever) is in the tank. Maybe one of these Xiaomi leak sensors could be modded for that?
And my second idea would be to use a load sensor, but not the one linked above. I’d try one of these, as they only have one point of measuring, that would work against all the movement of the fluid:
https://www.amazon.com/Geekstory-Weight-Electronic-Kitchen-Weighing/dp/B079FQNJJH/ref=sr_1_4?dchild=1&keywords=load+sensor&qid=1616638778&sr=8-4
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Now that’s an interesting idea ! Water leak sensors typically don’t use pressure detection, but just measure the resistance between two pins exposed to the potential leaked liquid. And I’d like to keep stuff wired whenever possible on board. But I guess I could hook a small wired liquid pressure sensor to an Arduino or similar. I’ll have to keep this in mind for future experimentation !
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You could automate the reset, also… Can’t think of exactly how atm, but I’m sure it could be done… Maybe with a sensor or switch in the nozzle opening?
A note about power… ESP devices (for instance, the D1 Mini and D1 mini 32, based on the ESP8266 and ESP32, respectively) have a “deep sleep” state that they can be set to, with a timer to pull them out at set intervals, or manually, via external ping or sensor even. When in this mode they use miniscule amounts of power. So technically, many of your sensors would hardly be noticed if configured right. Not so sure about many of the commercially available switches and sensors…likely no such luck there…but I prefer to create my own solutions if possible anyway. May not be as “purdy”, but it’s a lot more fun and educational.
Oh I’m sure it could ! But you know, the thing with boats is, if you use them in a more serious way than just the occasional weekend fishing trip, the farther away from the coast (and possible help) and the longer you sail, the more you tend to avoid all sorts of things and contraptions (especially electronic ones) that may be a point of failure, unless they are absolutely essential. The simpler, the better. In a worst case scenario, you might have to repair something while at sea, at night, in a jumping boat, under pouring rain and with your passengers being seasick
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My premise at home, too. Everything has to work without HA or any system at all, just the way it was before “smart”. But that doesn’t mean, you could make it a little more luxurious. For a (water) tank I’d always have a “manual measurement” as standard, and the app functionality on my phone.
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That’s a good premise to go by in any situation !
There’s one more serious pita in a marine environment that you don’t have at home: galvanic electrolysis. Seawater is a great electrolyte and turns anything it touches that contains different metals into a battery. Which then proceeds to eat up your stuff. Literally. Cables, connectors, PCB traces, your shaft and propeller, engine, your mast, even your boat hull if it’s made of metal. The big parts are usually (more or less) protected by zinc anodes, but electronics are complicated. You need to seal everything that is supposed to last. You have to use tinned strand cables, because normal copper strands will be eaten to their core, hidden below the insulation. You may have to use special galvanic isolation circuits if your stuff needs a ground plane.
I’ve seen a Raspberry Pi who had all it’s ground traces on the PCB eaten away within a few months, it crept under the conformal coating. The worst thing is that nice and proper grounding can actually make it worse…
True that… How many time have we seen people re-wire a light, or an antenna, or something similar using non-marine-grade replacement, only to have it fail a few months (or weeks) later due to corrosion. Biggest problem is in purchasing a new boat, and finding out two months later what was sloppily done with “normal” parts just to raise the price for the sale. Even with proper enclosures, salt water and the ever-invasive corrosion tends to sneak in eventually. That’s why you always keep at least one or two spares onboard. But that’s another reason I love the rPi, ESP32 and 8266, and similar devices (and a lot of hot-glue!), combined with Home Assistant so much. The parts are inexpensive and easily replaced if they fail. And the integration is so easy!
For future readers from Google search results - I spent a long time going through old forum topics here, eventually figured out how to get the set_location feature working, and wrote a detailed post about it here:
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Hope you get some traction with your website. There is a huge use case for Home Assistant in the boat and RV community that I am very excited about. I think there should be a complete sub-forum on this site just devoted to the boat/rv community. Have you dabbled in HA with CANBUS yet? I want to pull basic engine data (oil pressure, temp etc) into InfluxDB for monitoring/preventative maintenance.
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Nice idea. I’m not likely to spend $300 on a Victron Cerbo GX just to get GPS into HA, unfortunately. But hey, if it helps anyone (including traffic to your site) it’s a good thing!
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@CaptTom It should also be possible without the Cerbo, too, I just wasn’t smart enough to figure out how to convert the serial data 
but if I figure it out, I’ll post an update!
@KevinE Thank you! I haven’t done anything with engine data yet, but planning to. I think it requires an extra YachtDevices chip to be able to get the data out / be able to read it properly
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@CaptTom I pull in GPS data into the HA in my RV using a $15 USB GPS receiver from Amazon. I installed gpsd and I’m using the HA gpsd integration. It was relatively easy and has been working great.
@KevinE I’m currently pulling in RV-C CANBUS data into my HA implementation. I’m planning on pulling chassis info into the HA system via a connection to the chassis J1939 port. I haven’t yet decided whether to connect a cable from the J1939 port to the HA system or use a ESP development board with a J1939 or ODB connector to read the data and forward the data to HA via MQTT.
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