3 minute read

Apple’s Magic Mouse: A Surprise An the power of convention

The Back-story

Something weird happened to me tonight.  My mouse ran out of batteries and after a few minutes of yelling and hoping to squeeze out another few minutes of work  I decided to actually stand up and replace them.

Easy enough.  I have a procedure for this and I can turn my brain to more important things.

  1. Open case
  2. Use portion of case to pry batteries out
  3. Locate a + sign
  4. Put + of battery facing the + sign
  5. Put next battery in the opposite way so that the + is facing the other direction
  6. Wedge case back on

I have used this procedure about 1,000,134 times and it has never failed me.  If there was anything in my life I could count on it was this.

But then, there was tonight.  After sitting back and my desk and trying to resume my work I realized my mouse wasn't working.  Fuck.  Did I break it?

Ugh, ok, maybe I mistook where the + is, sometimes I do that.  So, I open the case to find WTF?!?! both of the + terminals in the magic mouse face the same way!!

Why This is the Way It Is...A Guess

OK, now I think I'll discuss this for a moment.

Imagine you are designing an electronic component that runs on batteries.  You need enough voltage and current to run your device and you have determined that two AA batteries in series would be great (maybe I'll have some posts about voltage/current/and regulators at some point).   This is also assuming that Apple didn't get the Magic Mouse to run on 1.5V.

Now, what is the best configuration to have them?

rf-decisionFor most of you, you would choose the option to have both of the + signs facing the same direction.  This makes it obvious which way the batteries go and there is less of a change of confusion.

So, why are electronics always always the other way (my guess)?

To answer this let's take a look at home we would wire these configurations so that the batteries were in series (you can trace from + to -).

Facing Opposite Directions


In the first diagram we see how the wiring gets aligned when the batteries + and - are inverted.  During manufacturing, it is cheaper to align the batteries like this.  This is for a few reasons.  The first is that a simple metal connection can be made between the + and - contact on one end.  This means less soldering and human interaction.


For example, see this part from Radio Shack.  It is a little hard to see but you can see how simple this part is.  All there is to it is a plastic out casing and some metal parts.  No soldering at all is required (and sells for ~$1.50).

Both facing up


In the  next, you can see what happens when both batteries are facing up.  There needs to be some sort of connection between the positive of one battery and the other.  This could be accomplished with a wire or some sort of integrated metal component.  Either way this part is more difficult to manufacturer and almost certainly has a higher cost.

Should I be happy or sad?

It's pretty cool that Apple went through the trouble of correcting this in their mouse.  I found it funny that I am so used to it the other way I don't even bother to look.  Kudos for them to try and do it the 'right' way.magicmouse-small

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