I have an idea for a sensor

[Homer]

Hey

Wasn't sure where to put this...

I want to make a sensor that will tell me when the level of my pool drops. I was thinking about running two wires into the pool in a discrete location and wire it up to the Arduino so that when there is no connection it trips. Would this work?

[zboblamont]

@homer Float switch/es would be a simpler to incorporate for a set-point, ultrasonic for range detection...

[skywatch]

@Homer Unless your pool is very sheltered there is always the problem of surface movement caused by wind or people in the pool.

Therefore you can only take reading when the pool is not in use and use a long average of readings to even out wave motion.

I guess you could insert a vertical tube into the pool and take readings from inside of it as it would protect against wave motion to some extent, but not all.

Even a float switch would oscillate on/off due to water motion, but is probably the best solution I can think of that would be cost effective.

[zboblamont]

@skywatch Didn't consider surface ripples when the pool is in use, good point..
A stilling tube would indeed help, and/or seek X repeat readings a minute apart to resolve variations to identify a consistent low.
Due to the unavoidable deadband an ultrasonic would however make for a less compact arrangement at pool level. Perhaps under a diving board or some other projection over the pool surface?

[Pieter]

@zboblamont If you are talking about a swimming pool, the chlorine/salt and other chemicals make for a very corrosive environment. so anything mechanical and electrical will not last long!

I want to make something similar (including, salinity, PH value etc) and have found the following from Adafruit: https://www.adafruit.com/product/3827 (not cheap) but if you want to measure the actual level instead of a max or min level as with floats. it might be of interest.

I have not tried it myself,as my pool automation is way down the list of things to do

[Homer]

Thanks for everyone's replies! You have all given me much to think about.

[PeteKnight]

I was watching something on TV the other day where someone was running a guest house in France and they had to have an audible alarm that sounds whenever someone falls in the pool. I guess it's intended for child safety.
The off-the shelf system that they added used an air pressure switch as the sensor and a key-pad to disarm the alarm. It re-arms after a certain time if there's been no activity.
Most washing machines (at least the front-loading variety) use an air pressure switch to sense water level and this acts as an interlock to prevent the door being opened when there's still water inside. These switches have a plastic tube and n internal diaphragm. When the end of the tube is below the water it creates a positive pressure in the tube, which distorts the diaphragm and operates a microswitch. Sounds a bit clunky, but they are very reliable. A switch of this type could be used to detect when the water level falls below a certain point.

The other thing is that most pools have an auto-fill system that operates like a toilet cistern. The problem with these is that if you have an undetected leak you can end-up with a large water bill before you know that anything is wrong. I'd add a flow-rate sensor on the inlet to the auto fill supply to see how much water is being used. It would keep the pool topped-up and record how much water has been used, and alert me if that exceeded certain limits - maybe with an electrically operated valve to shut-off the supply in those situations.

Pete.

[zboblamont]

@pieter My pool doesn't exist, so it's even further down my list of things to do

Plenty of waterproof and immersable float switches on the market to avoid corrosion issues and satisfy the OP's requirement to detect low level, but requires installation in the pool, even at the periphery this may be intrusive.
If an overhang is available, a $10 waterproof ultrasonic with a waterproofed radio node should provide highly accurate readings, ironing out the ripples @skywatch highlighted is possible in the sketch, but the advantage is no physical intrusion to the pool.

Likewise your own chemical analysis requirements could be solved remotely if you can run some tube unobtrusively, a small $10 persistaltic pump presenting a fresh sample to the analyser. Only direct temperature would be left to figure.

[bjacobse]

You can also use airbubbles pressure sensor to determine your water level
https://playground.arduino.cc/Main/Waterlevel/
https://automationforum.in/t/what-is-a-bubbler-level-gauge/2503

[wallyllama]

How about a sealed tube with 2 copper strips down the inside, then measure capacitance?

Kind of like this:
https://www.instructables.com/id/Capacitive-Fluid-Level-Sensor/

[zboblamont]

@bjacobse Ditto for submerged pressure transducers, but if the target range is say 20mm H2O, sourcing a sensor with 2mBar or better sensitivity could prove challenging, before considering energy used by the compressor.

[kimot]

https://www.aliexpress.com/item/4-20MA-level-transmitter-Level-Controller-input-type-level-sensor-fire-water-tank-level-indicator-rang/32803093892.html?spm=2114.10010108.1000014.7.tneAib&traffic_analysisId=recommend_3035_null_null_null&scm=1007.13338.84782.000000000000000&pvid=806a62d9-21a3-4a55-95c3-7d5b2c45793b&tpp=1