Tuesday, March 20, 2018

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!

Actuation

Use a solenoid valve:
DIGITEN DC 12V 1/4" Inlet Feed Water Solenoid Valve Quick Connect N/C normally Closed no Water Pressure

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:

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:
Image result for intel movidius
Plus the fact that I can get this to trigger only on cats is really neat.


No comments:

Post a Comment