I normally don’t care that iPads don’t vibrate.  However, for a study at the VEMI Lab we’ve been looking at testing different types of vibration as a haptic interface for low vision users of mobile devices.  Unfortunately, most mobile devices that have vibration built in are phones, and phones have small screens–not ideal for some of the experiments we want to run.  The only larger mobile touchpad we have on hand is an iPad, but as I said…they can’t vibrate, at least not without some help.

Putting a motor on the outside of the case wasn’t very productive, either on the aluminum back or the glass: the little motor from Radio Shack just isn’t strong enough to provide a useful sensation on the outside.  So, the help has to be internal, which means breaking into the iPad.  As documented here, this isn’t for the faint of heart (though it is easier than it looks).

While putting a motor in is nice, we also need it to be driven by activity on the iPad.  There are a few ways to do this, but I took a bit of a Gordian Knot path and decided to just run the motor directly off an audio signal.  The iPad obviously has a headphone jack on it, but since we’re in a lab environment I also wanted to be able to power the motor off external audio sources for a bit more flexibility.  That led to this:

iPad with audio jack

 

Yes, we drilled a hole in the back of an iPad and stuck an ugly wire through it.  Yes, we’re going to Apple Hell.  But it works: the iPad now vibrates stronger than most phones, over its entire screen.

A few build notes:

Attaching the motor to the iPad’s case was a bit of a pain.  In the end it took some liquid weld epoxy to hold it in place.  In addition, it’s pretty cramped in there, so there wasn’t room to add a second motor as I had planned.  (Hey, audio is stereo, might as well run two motors, right?  Ah well.)

Inside mounting of the motor.

 

Breaking into the iPad is as annoying as advertised and I broke off most of the pins that hold the glass in place on one side.  Luckily, once it’s back in it’s case you’d never know I opened it.  A quick cut in the case protects and hides the wire coming out of the iPad.

Back of the iPad in it's case, with just the jack extension showing

 

The overall system is a bit more complicated than just running from the headphone jack to the new input.  Not only is there not enough power to run the motor, but it needs to be rectified.  Again, since this is a lab situation, I can afford to be a bit bulky with my solutions:

The complete setup, with amp and rectifier

 

The silver and black box is a headphone amp, which boosts the signal enough to turn the motor (and gives me the ability to adjust the vibration strength just by changing the volume).  Between the amp output and the iPad is a project box that just takes one audio jack, runs both channels through a pair of rectifier diodes, and sends it back to an output audio jack.  I probably could/should have thrown in a smoothing capacitor, but it wasn’t necessary.