CAP - Water Fountain: Engineering

Intro

My cat only drinks from the tap. He doesn't know how to turn the water on or off. So I need a system to get him water when he wants it.

Requirements

• Need
• Clean install
• Provide water when cat goes to the sink
• Don't trigger on humans
• Turn water off when cat is done
• Run for a month between charges
• Want
• Tweet/ notify when cat gets water for peace of mind
• Notify on low battery
• Easily integrated and removed

Engineering

Clean install

I picked a sink I can easily modify to include a spout, and he's used to drinking from. There is no outlet nearby that I can wire to cleanly. So I'll have to use a battery.

A clean install means no visible wires or tubes running through the sink. 

Provide water: turn off/on when cat comes around

Control

ESP 8266 Thing from Sparkfun promises low-current draw and WiFi, nice!

Sparkfun Thing board

Actuation

Use a solenoid valve:

Sensing

Sensor selection/ design will be a trade off between accuracy and visibility.

IR sensor

• Pros
• Pretty standard way of doing automatic sinks
• Cheap sensors
• Cons
• Wires
• Very visible sensor
• Compact or clean looking versions are hard to find ($$)
• Might trigger when I'm using the sink (not desired)

Capacitive something...

• Pros
• Clever sensor placement/ design could exclude everything but the cat
• Minimal
• Cons
• Might be visible
• Not really straightforward

Piezo loadcell

• Pros
• Minimal, very clean, invisible
• Cons
• Difficult to design against non-cat triggers (extra weight in the sink will cause it to fire)

Machine vision

• Pros
• Fun to make
• Could become very good at cat-only triggering
• Cons
• Overkill
• Visible sensor/ camera

Run for a month between charges

Add up all the current consumers and estimate Oppie's drinking habits. Pretty simple.

• ESP8266
• Awake: ~200mA
• Standby: ~0.9mA
• Solenoid valve ~ 400mA

Oppie drinks water for ~ 10 minutes a day. 31 days in a month = 310 minutes.

I picked this thing:

Battery Pack

The ESP may actually consume less current while running, but assuming some leakages here and there keeps things conservative.

Conclusions

• Control and actuation is pretty straightforward. No decisions.
• Battery pack looks like it should be sufficient
• I'll use machine vision to detect the cat. Especially considering how cool/easy this thing looks:

Plus the fact that I can get this to trigger only on cats is really neat.