Empty water bottle detector

[rexxar]

My rabbits have two water bottles on the side of their cage, and it's kind of hard for us to tell when they're empty, so I wanted to set up a small project to detect when they're empty, and beep at us to remind us to refill them.

I can't put any holes into the bottles, that would break the vacuum and they'd leak everywhere, so I was thinking I could float a magnet in the water and have a reed switch at the bottom to detect it. Unless there's a better way of doing it?

I'm going to have a 555 beep piezo buzzer to alert us, but I'd like it to wait about 5 or 10 minutes between beeps. Is there a simple way to do that?

[NiHaoMike]

If the rate at which they empty is predictable, what about just use an alarm clock to remind you at a good time?

Another option is to add two strips of foil tape to the outside of the bottle, making a capacitor.

[JackOfVA]

I can think of complicated ways to detect level without penetrating the bottle wall - such as a pair of copper or aluminum strips in parallel applied to the outside bottle wall and looking for change in capacitance between the two strips with a trip point when capacitance/water level reaches some certain point.

But, if you are looking for a simple detector perhaps you could support the bottle(s) with springs so that when the bottle level drops below some particular level, the bottle will be pulled up by the spring such that a magnet operates a reed switch. Totally non-intrusive and relatively simple to implement the switch.

Or you might be able to use an LED and photo sensor - the water will refract the LED's light beam (as well as the bottle wall, of course) so that the LED spot will shift position depending on whether the path is bottle wall - water - bottle wall or bottle wall - air - bottle wall. This should also be relatively easy to implement with a self-contained light detector / switch.

[AndyC_772]

I think whatever technique you use to detect the liquid level, you'll want a real-time clock in the system somewhere. Otherwise you'll keep getting woken up at stupid o'clock in the morning by a bleeping rabbit hutch... the novelty will wear off quite quickly IMHO.

[rexxar]

I can think of complicated ways to detect level without penetrating the bottle wall - such as a pair of copper or aluminum strips in parallel applied to the outside bottle wall and looking for change in capacitance between the two strips with a trip point when capacitance/water level reaches some certain point.

That sounds interesting, there'd also be no wires near the floor for them to chew on. How would you implement this? Would it just be easiest to use an Arduino?

I think whatever technique you use to detect the liquid level, you'll want a real-time clock in the system somewhere. Otherwise you'll keep getting woken up at stupid o'clock in the morning by a bleeping rabbit hutch... the novelty will wear off quite quickly IMHO.

I was going to use a photoresistor to do this. I didn't want to get a micro controller involved, mostly because I don't know C 

[mariush]

Two wires inside the bottle, insulated almost up to the bottom... measure resistance every few minutes. If water, you get one resistance, if air (and uninsulated tips dry up) then you have another resistance.

Another idea would be to have some kind of material that reflects/refracts light differently when wet, then use infrared emitter and receiver and if infrared goes through you know there is (or isn't water at that point).

 Maybe use some of that material that's used in lcd filters ... tie something that floats in the corner of a square of that material, when bottle is full the material stays up, when you're low on water, it goes down over the other material making it opaque, blocking light.

[filip_cro]

If you are god at physic try using reflection from surface when water level is low. Maybe floating mirror would work better? Or barier which can float and block light in some moments?

[houdini]

Why do all that stuff just mount it with an small insulating spring separating the hook from another plate when it empty it will be light enough to push it up so either have this make or break a contact that triggers a whatever.

[deth502]

Why do all that stuff just mount it with an small insulating spring separating the hook from another plate when it empty it will be light enough to push it up so either have this make or break a contact that triggers a whatever.

wasmy first thought as well, but as i was pondering a reply whilst reading the others, i had time to think on it, and i believe that the mere act of the rabbits drinking from it would jostle it around enough to give enough false signals to make it unreliable.

[codeboy2k]

Why do all that stuff just mount it with an small insulating spring separating the hook from another plate when it empty it will be light enough to push it up so either have this make or break a contact that triggers a whatever.

wasmy first thought as well, but as i was pondering a reply whilst reading the others, i had time to think on it, and i believe that the mere act of the rabbits drinking from it would jostle it around enough to give enough false signals to make it unreliable.

Debounce it LOL  No really!

[Skimask]

Motion switch and a watchdog timer.  Motion switch resets the watchdog timer.  Watchdog timer triggers the alarm.

Rabbits drink water, move around, reset the watchdog timer.
Water runs out, eventually rabbits pass out from lack of water, watchdog timer runs out, alarm activates.
Simple eh? 

[JackOfVA]

I can think of complicated ways to detect level without penetrating the bottle wall - such as a pair of copper or aluminum strips in parallel applied to the outside bottle wall and looking for change in capacitance between the two strips with a trip point when capacitance/water level reaches some certain point.

That sounds interesting, there'd also be no wires near the floor for them to chew on. How would you implement this? Would it just be easiest to use an Arduino?

I think whatever technique you use to detect the liquid level, you'll want a real-time clock in the system somewhere. Otherwise you'll keep getting woken up at stupid o'clock in the morning by a bleeping rabbit hutch... the novelty will wear off quite quickly IMHO.

I was going to use a photoresistor to do this. I didn't want to get a micro controller involved, mostly because I don't know C 

A pair of foil traces (burglar alarm foil, or copper foil from the arts and craft shop) applied to the outside of the bottle and then taped or glued into place.  The electric field between the two foils will be both inside and outside the bottle.   And some of the field will be within the water.  Hence the capacitance will be a function of the water level.

There are LOTS of questions about the real life usability of this idea - such as whether the change in capacitance will be large enough to reliably measure.  With the right test gear, it would be simple enough to toss a prototype together and use a capacitance meter to measure the foil strip to foil strip capacitance with various water levels. Would also want to look at stability with temperature and a few other things before deciding it's the right way to go.  It's elegant but a simple solution has more going for it than an elegant but unreliable approach.

Another idea would be to use one of the robot ultrasonic distance sensors - since the speed of sound is much greater in water, if you measure the distance across the bottle diameter it will be much smaller when the sound path is in water than when the water level drops below the sensor.

https://www.bananarobotics.com/shop/US-100-Ultrasonic-Distance-Sensor-Module?gclid=CJ-b2LaQ8roCFcTm7Aod5G0AfQ

This sensor has both a digital and analog output - so you could use a microcontroller of whatever flavor you prefer or it could be done with a simple comparator and an RC filter network. 

Again, lots of details to pay attention to here, but it's probably a safer bet than measuring capacitance.

[rexxar]

I can think of complicated ways to detect level without penetrating the bottle wall - such as a pair of copper or aluminum strips in parallel applied to the outside bottle wall and looking for change in capacitance between the two strips with a trip point when capacitance/water level reaches some certain point.

That sounds interesting, there'd also be no wires near the floor for them to chew on. How would you implement this? Would it just be easiest to use an Arduino?

I think whatever technique you use to detect the liquid level, you'll want a real-time clock in the system somewhere. Otherwise you'll keep getting woken up at stupid o'clock in the morning by a bleeping rabbit hutch... the novelty will wear off quite quickly IMHO.

I was going to use a photoresistor to do this. I didn't want to get a micro controller involved, mostly because I don't know C 

Another idea would be to use one of the robot ultrasonic distance sensors - since the speed of sound is much greater in water, if you measure the distance across the bottle diameter it will be much smaller when the sound path is in water than when the water level drops below the sensor.

https://www.bananarobotics.com/shop/US-100-Ultrasonic-Distance-Sensor-Module?gclid=CJ-b2LaQ8roCFcTm7Aod5G0AfQ

This sensor has both a digital and analog output - so you could use a microcontroller of whatever flavor you prefer or it could be done with a simple comparator and an RC filter network. 

Again, lots of details to pay attention to here, but it's probably a safer bet than measuring capacitance.

That sounds like a good idea, but Google tells me that rabbits can hear up to 40-45kHz, so I'm afraid the noise would scare them away from their cage. I tried it on them, and a ~40kHz tone freaked them out, so that's not gonna work.

I was messing around with an IR LED and if I get the angle just right, I can get the light to bounce off the surface of the water. I think this will work for level detection, but that still leaves the issue of the long interval between alerts. Would a 555 work for such a long interval?

[jeremy]

Um, perhaps I'm crazy for suggesting this, but why not just weigh it? Buy one of these cheap chinese scales, hop inside and mod it a little with a Schmitt trigger.

I've done this before...I needed to see how much water was in a container....

[ElektroQuark]

Change water in a daily basis, they need fresh water.

[Tris20]

Two metal rods vertically inside the bottle. Both full insulated except one is exposed at the top(in air), the other exposed at the bottom( submerged). When resistance of bottom exposed rod is equal to the resistance of top exposed rod then the bottom is now exposed to air, therefore empty. Pretty sure this is along the same lines as other suggestions but this is how I would do it. But the device would also go off if you filled the bottle too much and submerged the top exposed rod.

Also, +1 for the timer. You don't want this going off at midnight

[deth502]

Change water in a daily basis, they need fresh water.

not playing the grammar police, but from your sig line i'm guessing your trying to learn. should be "on a daily basis" as in doing it on a schedule, or doing it on time.

[dannyf]

Empty water bottle detector

Two pages of sophisticated technological solutions to a problem that can be simply solved with love, care and responsibility.

[ddavidebor]

Change water in a daily basis, they need fresh water.

not playing the grammar police, but from your sig line i'm guessing your trying to learn. should be "on a daily basis" as in doing it on a schedule, or doing it on time.

Policeman, that's a international forum, not british language fan club...

[Alana]

Empty water bottle detector

Two pages of sophisticated technological solutions to a problem that can be simply solved with love, care and responsibility.

One hand - you are correct, other hand - this is interesting tech project anyway.
Btw when i had guinea pigs no sensors were needed, when hungry they made more noise than all my buzzers put together.

[AndyC_772]

Policeman, that's a international forum, not british language fan club...

You did see the signature right below the post in question, right?

I'm not an English native speaker, please correct me if I write something wrong

[ElektroQuark]

Change water in a daily basis, they need fresh water.

not playing the grammar police, but from your sig line i'm guessing your trying to learn. should be "on a daily basis" as in doing it on a schedule, or doing it on time.

Thank you VERY much.


On the subject:

A spring with a switch could do the job: water reservoir pending of the spring closing the switch under it. The spring should be strong enought to elevate the reservoir when it is empty releasing the switch.


Edit:

Sorry, I see now it was already suggested.

[BillyD]

Oops, just realised that rexxar had already thought of my suggestion about IR led and receiver.

[rexxar]

Those poor rabbits

As has been mentioned, show some love, take care of them properly. At the very least change their water once a day (every day) for fresh. Why have them if you don't want to have anything to do with them?

That's quite insulting, actually. I do take care of my rabbits, which is why I've paid hundreds of dollars to have them spayed/neutered and given them my entire living room. Their cage is where their food, water, and litter box is, it's always open. You don't know how I treat my rabbits, don't make assumptions. Besides, I see no reason to change the water in a sealed, shaded container every day, so long as I wash it between fillings. Ever bought bottled water? Did you empty and refill all the bottles daily so they're "fresh"?

I'm very busy with work and school so I sometimes don't notice the bottle is empty until the rabbits tell me, so I'd like to have a reminder. I thought this would be a fun project, and I'd learn some more about 555s, or micros, or whatever I decided to implement.

So, thanks for your input, but I'm pretty sure I know more about rabbit health than you do.

[fcb]

Two metal rods vertically inside the bottle. Both full insulated except one is exposed at the top(in air), the other exposed at the bottom( submerged). When resistance of bottom exposed rod is equal to the resistance of top exposed rod then the bottom is now exposed to air, therefore empty. Pretty sure this is along the same lines as other suggestions but this is how I would do it. But the device would also go off if you filled the bottle too much and submerged the top exposed rod.

Also, +1 for the timer. You don't want this going off at midnight

You will form a electrolysis cell, and likely strip metal ions from the electrodes, potentially poisoning your bunnies.  If you really must use electrodes, then only apply a small current on an infrequent basis (perhaps 0.1 seconds every hour, etc...) to make your measurement.

Depending on your level of expertise and/or motivation, and the assumption that you are looking at this as a challenge, here are some other ideas:
1. Optical, using the change in refractive index between air/water to alter the light path.
2. TDR - time domain reflectometry, wind a tight coil of wire on a hollow-former.  Send down a fast pulses and measure the time they take to return (easier than it sounds, and you can average it over perhaps 1E6 pulses).
3. Wind a coil round the outside of the bottle, use this in a colpitts oscillator and measure the frequency change.
4. Put a colored ball in the bottle, use a webcam with something like the roborealm/opencv machine vision.