Hey! So, I'm looking for a food safe water sensor.
Ideally, it would be mounted outside of the water container facing down into it and tell me when the water passes a certain level (maybe ultrasonically?) This would be best because I'd have no concern at all for food safety (because it wouldn't be in direct contact with the water) and I also wouldn't have to clean it nearly as often.
If that's not doable, I'd need something I can mount outside of the container (specifically a dog water bowl) that would be suspended down into it, perhaps a right angle float switch. The reason I'd prefer that it be outside of the bowl is for ease of cleaning - I regularly need to remove the bowl and wash it, so I'd rather not have electrical components connected directly to the bowl.
The project is an auto-filling water bowl. Eventually, it will (hopefully) include an auto cleaning system, where once every few hours the bowl auto-empties and then refills. This is necessary because as a dog boarder I care for many dogs, and a communal water bowl carries certain risks.
You are looking at auto refill every few hours so why bother with level? Surely the dogs will survive if the bowl is emptied within this time.
Why not simply empty the water and refill for a fixed time? Or have a short top up flow at half the time if the few hours is too long.
This will remove the need to monitor every bowl and hence simplify the design. All bowls would be same size and initially filled to say half then top up to 3/4 at half time.
Auto clean would require mechanical arrangement to brush the bowl so the design is up to you.
weedpharma:
You are looking at auto refill every few hours so why bother with level? Surely the dogs will survive if the bowl is emptied within this time.
Why not simply empty the water and refill for a fixed time? Or have a short top up flow at half the time if the few hours is too long.
So this is a really interesting idea. I took a few hours to think about it...
There are a couple issues with this approach:
I specialize in "special needs" dogs, ie dogs with kidney problems, diabetic dogs, etc. Not having access to water could be quite distressing, and potentially (though unlikely) even dangerous to their health. The obvious solution would be more frequent emptyings... but that would waste a lot of water. I'm trying to find a sweet spot between wasting water and maintaining hygiene.
Another issue is water pressure, which changes regularly. I'd need a well calibrated flow sensor... luckily, I've already ordered one as part of a fail safe... if the water level sensor is damaged or what-have-you, the flow of water will shut off after 30 seconds (maybe less... we'll see) and an alarm buzzer will go off to notify. I guess I could add careful calibration to account for water pressure...
Also, the number of dogs changes substantially - holidays, summer vacation, winter lulls... Not to mention, some dogs drink a LOOOOT more (such as those with kidney or thyroid issues) and some are just big. I've had days where I had 10 tiny dogs- and days when I've had 10 large ones AND 5 tiny ones. I don't feel that having a dozen settings would work.
So anyway, while your idea was really interesting, I don't think it's right for my use case. But thanks! Your proposal really made me think through the whole system.
Peter_n:
Radar or capacitive or ultrasonic can 'see' through the walls of a container.
This is a good idea, except for a couple things...
First, that sensor needs to be glued to the outside of the container (unless I'm mistaken), which makes it impossible to properly wash. Also, I'm not sure how I could waterproof the sensor (dogs are... messy drinkers) without interfering with its function.
Second, plastic containers can't be used due to porousness (microscopically), which leads to bacterial growth which is resistant to all but the most intense washing. So I'm limited to glass (no way), ceramic (maybe) or stainless steel (the industry standard). Glass is just too dangerous. Ceramic seems fine and is within the margin of safety I find acceptable (less shards, less fragile) but that doesn't solve the mounting issue or the waterproofing (not resistance... waterPROOF).
Still interesting idea. I'll continue brainstorming.
Right now I'm thinking a pressure sensor hooked up to a food safe tube that's suspended into the bowl. As water enters the tube from below, the water pressure rises. The biggest advantage is that I'd be able to remove the tube for periodic cleaning or replacement. The disadvantage is spotty reliability (I've seen some that say that it works, some say it's troublesome). Also, I wonder if the extremely high humidity from the water at the bottom of the tube would damage the sensor.... it can't be good for it! I'd probably set up a U bend, but some would still drip over and steam up again...
When the bowl is always in the same place, you can use an ultrasonic or IR distance sensor. The sensor will be pointing downwards into the bowl from a distance of maybe 50cm. It is accurate enough and you can easily detect when a dogs head is in the way.
Or perhaps something very simple: something that floats with a stick pointing upward. At the top of that stick perhaps a magnet and a reed switch or hall sensor to detect it.
Is it possible to add something to the water against bacteria ? Perhaps a herb like hyssop, or some tea tree oil, or green tea ?
A number of pens.
Each pen can have a variable number of dogs.
The dogs can be of various sizes.
Water bowls would be stainless steel.
The water usage would vary depending on size of dogs in each pen.
Pressure of water supply is variable.
You want to empty the bowl before refilling.
Each bowl should have its own level sensor.
I assume the bowls will be mechanically fixed to avoid knocking over and mis-reading sensors. If this is so, you may be able to simply have a probe in the bowl and measure between the probe and bowl.
To empty the bowl, you will need a drain and solenoid valve. The valve will need to be a zero pressure to activate type. Most cheap valves require pressure to operate.
The refill solenoid can be a basic irrigation type. I assume you have mains power to supply 24vac.
Water supply pressure regulators are available.
Looks like an interesting project. There is however a lot more than simply needing the water sensor!
What about a pressure sensor under the bowl? I mean a scale.
Another idea can be an optical fiber where a light beam is reflected back if the fiber is outside water and it is not reflected when the fiber is inside water.
A number of pens.
Each pen can have a variable number of dogs.
The dogs can be of various sizes.
No pens - this is a communal setting. A kinda high class dog boarding service, where the dogs live with a person.
So yeah, I'd forgotten that not all valves can be gravity fed! d'oh! I'm pretty sure, though, that the exit valve I've ordered is already fine for gravity feeding. I've ordered the food safe version of the following in 1/2" 12v: http://www.aliexpress.com/snapshot/6312430233.html
Water pressure is not terribly variable. We actually have very stable water pressure, but I'd rather plan for a potential issue than ignore it and be unprepared when it comes up. You never know.
The bowls will be fixed in place.
I've already got a simple prototype in place. the water sensor is two electrodes (simple enough, and safe in the very short term). There's a cheap solenoid in place as well. When the water level drops, the valve opens. I haven't set up an exit valve yet.
I really like ZoomX's idea of a pressure sensor UNDER the bowl. I've been considering this idea. It seems like an ideal non-contact solution. The question is, how do I set that up? I have no idea....