Did you feed the dog? (part 2: physical interaction)

What kind of physical interfaces am I inspired by?  Intuitive ones.  Ones that behave the way you expect them to.  Ones that have a few clear and simple operations.  Ones that have very few states to keep track of.

  1. Doors that need to be pushed should look pushable.
  2. Buttons that control lights need to be found in the dark.
  3. If I can’t tell if you’re open or closed, or on or off, you’re doing it wrong.
  4. If I can’t tell how to open or close you, or turn you on or off, you’re doing it wrong.

So, my dog food logger should be intuitive.  What’s important to keep track of?  When the dog was fed. What are the possible states?  Well, if you want to get very detailed, you can have a timestamp, and perhaps we’ll do that on the digital side of things, but the actual human meaning of the timestamp will be evaluated as “breakfast” or “dinner”.  Really only two states.  I like the idea of a rotary dial behind a faceplate with a cut-out window – the dial can spin to indicate the present state, and hide the other behind the faceplate.

images (1)

Kind of like a scale, only with two discrete portions instead of a number line.

Now that I’ve decided on a basic form let’s remember how we’re going to use this thing.  We’re going to look at it, and we’re going to toggle it.  That’s the extent of the physical interaction here.  Sounds pretty basic.  What does it mean for our physical design?  Well, it should probably be big (the easier to see) and have a simple handle/manipulator (the easier to toggle).  I can do that.

Let’s not forget that I want to be able to check the time of the last feeding from my phone.  Gotta be able to read the dial remotely.  There are a ton of ways I could read the position of the rotary dial – a real budget solution might be to just glue some contacts on the back and have some wires that drag against them, but that’s pretty finicky in terms of physical solution.  The rotary dial approach has an awesome advantage, though, because we have the axis that we can tie in to.  I have some rotary encoders, but those require constant attention to be able to determine position.  On the other hand, a potentiometer can tell me exactly where the dial is.  It won’t spin freely – a pot usually only gets 200 degrees of movement or so.  On the other hand with only two choices, free spinning is not a huge requirement.

So here’s the idea:


A faceplate with a semicircular cutout, and a spinner wheel which will be mounted behind on an axis.  Since the potentiometer which we’ll mount behind won’t be able to rotate freely, we’ll put a knob on the edge of the wheel, which will both function as a handle to rotate it and a stop to prevent it from rotating too far.

Next up: cutting and assembling the first draft.

What do you think?