I revised this project. Here are the changes.



I don't think I've ever used so much super glue so many ways to build a project before. I glued the parts to the back of the Sonalert and point to point wired it with small pieces of wire. I then super glued the Sonalert to the box, lining up a hole in the box I drilled with the hold in the Sonalert. I glued the LED and wires in their respective holes to keep them from wiggling.



Parts List
2 Leads - one red, one black, with alligator leads already attached.
Medium Project Box
AAx2 Battery Holder w/ Batteries
Small NO Push Button
Sonalert
IC - 7555 CMOS
Q1 - 2N2222A
Q2 - PN2907A
C1,2 - 470μF 6.3VDC Electrolytic
R1,3 - 1MΩ
R2 - 1.5KΩ
R4 - 10MΩ
R5 - 470Ω

It works as predicted, I used picture hanger wire for the electrodes and clipped to the wires. The wire I used for the probes was fairly rusty after 5 months of use, but was still functional.

When the pet water dish is empty it will sound the sonalert for 1/2 seconds every 6 minutes. The idea is to be a gentle reminder, not scare the pets. I have repurposed the LED as a battery test, as I needed that function and the sound was what I am keying from after using it for several months. The LED only draws 1ma when lit.



I used a combination of Dead Bug Prototyping and Manhattan Style Prototyping. I used the description on pages 9-11 of the Manhattan Style document to make the circular pads for the sensor contacts.



I used Velcro to attach the finished box to the top of the water jug as shown.



The pictures are from my new smart phone. I can get used to these features, but still have some learning to perform on it.

 

This is the project before I revised it, kept for archive purposes.

I finished the project I described here.


I don't think I've ever used so much super glue so many ways to build a project before. I glued the parts to the back of the Sonalert and point to point wired it with small pieces of wire. I then super glued the Sonalert to the box, lining up a hole in the box I drilled with the hold in the Sonalert. I glued the LED and wires in their respective holes to keep them from wiggling.

There is no on/off switch, I place current draw under 10μA. If I get energetic I may add a simple push button / LED circuit as a battery tester later, it is hard to tell what the state of the batteries are otherwise.

Parts List
2 Leads - one red, one black, with alligator leads already attached.
Medium Project Box
AAx2 Battery Holder w/ Batteries
Sonalert
IC - 7555 CMOS
Q1 - 2N2222A
Q2 - PN2907A
C1,2 - 470μF 6.3VDC Electrolytic
R1,3 - 1MΩ
R2 - 1.5KΩ
R4 - 10MΩ
R5 - 10Ω







It works as predicted, I used picture hanger wire for the electrodes and clipped to the wires.

When the pet water dish is empty it will flash the LED and sound the sonalert for 1/2 seconds every 6 minutes. The idea is to be a gentle reminder, not scare the pets.

I used a combination of Dead Bug Prototyping and Manhattan Style Prototyping. I used the description on pages 9-11 of the Manhattan Style document to make the circular pads for the sensor contacts.

I used Velcro to attach the finished box to the top of the water jug.

 

Neat. I'd like to see one more photo - the entire operation, dish and all.

It'll be interesting to see how it holds up. When I clean the cat's water fountain I often find a kind of bioslime, primarily on the replaceable filter but also in slow-moving areas. I'd guess the slime will be a bigger issue than any corrosion from the small current.

Consider the metallurgy of whatever touches the water. I don't know what paperclips are made of. Obviously, if they were made of lead or mercury, you wouldn't want to use them. Chrome sounds bad, too. We all drink from copper pipes, so I'd be tempted to go with copper even though it's more likely to corrode.

 

The "electrodes" will disappear in days because they are biased with DC. You need to excite them with <1Vpp AC, and use an AC Ohmmeter circuit...

 

Any electrode, or were you referring specifically to my comment about copper?

 

The "electrodes" will disappear in days because they are biased with DC. You need to excite them with <1Vpp AC, and use an AC Ohmmeter circuit...

At less than 3uA I kinda doubt I'll see much action for a while. You have to keep things in perspective, this is a very low power low current system.

I may see something in a week or two, but I doubt it.

 

At less than 3uA I kinda doubt I'll see much action for a while. You have to keep things in perspective, this is a very low power low current system.

I may see something in a week or two, but I doubt it.

At 3 uA, that is 0.25 coulombs per day.

Faradays constant = 95000 coulombs per mole electrons (round to 100k for easy math)

400,000 days per mole of electrons.

2 electrons per copper atom to oxidize brings it up to 800k days per mole (63 g) copper.

Or about 13000 days (35 years) per gram of copper.

So, you will loose about 30 mg per year.


In summary, it's a DIY watering dish, not a passenger aircraft.
Cost (severity) of failure is minimal, probability of failure is minimal.

 

I put probe current at 2.5uA, so it is less than that. Thanks for the math, I didn't have the math tools or brains. I just knew if I kept the current as small as possible it would slow things down a lot, not to mention making the batteries last. The first electrodes are kludges, I'll tweak the shapes later. I'll also post any developments as I see them.

I have a technicians view of the world, this is an example.

 

I put probe current at 2.5uA, so it is less than that. Thanks for the math, I didn't have the math tools or brains. I just knew if I kept the current as small as possible it would slow things down a lot, not to mention making the batteries last. The first electrodes are kludges, I'll tweak the shapes later. I'll also post any developments as I see them.

I have a technicians view of the world, this is an example.

I did some work with a plating company and I knew hundreds of amps were used there to get appreciable rates of metal transfer. When I saw your 10M ohm resistor, I knew the world would be essentially standing still at micro-ohm currents and it was a pretty good design. I only did the math to humor myself.

 

... When I saw your 10M ohm resistor, I knew the world would be essentially standing still at micro-ohm currents and it was a pretty good design. I only did the math to humor myself.

Thanks for doing the math. I learned something from it...

 

Well documented project!
If you did another one I wonder if you would use a perf board or glue it again.

 

Not for this kind of project. It was very quick and simple. I did have one minor problem where a solder joint wasn't made, but it was easy to troubleshoot. Basically it was a one of a kind project, good for an evening or two..

What took me so long is punching out the printed circuit board pads I used for the sensors. I had to repair my Harbor Freight deep throat punch by buying some new metric screws. I now have a pill bottle with 10 or so similar pads ready to use.

 

Learnt so many thing from your post, thank you so much for sharing your thoughts and invention.

 

Hi Wendy,
I think the 7555 is a popular 555 timer. Why you mentioned as CMOS, cannot I use ordanary one. The CMOS version not available around here.

 

@Wendy

Shall I make you a Pet Water Dish Alarm System using PIC12F1840, BC337, 3.3V Buzzer ?

https://www.fairchildsemi.com/products/discretes/bipolar-transistors/small-signal-bjts/BC337.html
http://www.tandyonline.co.uk/miniature-3-3v-pcb-buzzer.html
http://www.microchip.com/wwwproducts/en/PIC12F1840

PIC12LF1840 can run from 1.8V

WDT will be used. The device wakes up reads the adc and then if needed turns on the buzzer for 3 seconds and then goes to sleep and repeats this once every 20 sec.

 

You can use the smaller eTape

http://milonetech.com/products/standard-etape-assembly

with a PIC12LF1840 and a 3.3V Buzzer mentioned in the previous post. This will give the reading of the water level in the pet water dish. When water level is low then you can fill it with a small pump controlled by PIC.


Your project is nice. It is simple and cheaper. Here I am attaching PIC12F1840 based project (not using eTape but using INT pin). SPST switch in circuit is replaced by alligator clips. When water becomes low INT pin is triggered and it plays a melody 3 times and then starts a timer and when timer. A counter is used in the timer interrupt and when this counter expires (approx 20 sec) then it plays the melody 3 times again and this process repeats till water is filled or battery dies.

See video in attached file. It contains audio.

 

I designed a PCB layout for your ICN7555 based circuit. It is a two layer board. If you want one layer board then I will design a new layout.
See if you can use this layout.

Cadsoft Eagle 7.6.0 format Schematic and Layout files are attached and also the PDF showing the actual size of the PCB.

 

Why use a programmable chip that requires special toolind just to pprogram when a simplle20 cent part wil work?This project was very simple and cheap Why build a lath toreinvent a wheel?555s are very available everywhere.Programmable is OK, not for baginners.

 

Hi Wendy,
I think the 7555 is a popular 555 timer. Why you mentioned as CMOS, cannot I use ordanary one. The CMOS version not available around here.

They allover mailoerder houses. I am flat on my backparalyzed with a stroke. Icould find one in seconds with Google.

 

Instead of an Alarm once can use a relay with a small pump like ones used in indoor fountains to pump water from reservoir to pet water dish or more easier is to fix a solenoid valve to the reservoir and turn it ON when water level goes low in the pet water dish. Two small float switches are needed and have to be fixed to the water dish.