Tuesday, January 3, 2012

Droid Razr Touch Screen Noise

Last month I got a new cell phone to replace my first generation Motorola Droid.  I decided to get the Droid Razr, another Motorola product, and I've been generally happy with it.  Some of the features just seem nuts to have in a cell phone, like HDMI output, and yet I've used it to watch a movie on a hotel TV.

One interesting sensitivity that I noticed today was that the touch screen keyboard became almost unusable while I had the Razr plugged into a wall charger.  I have been using the "Swype" mode, which allows you to enter entire words as a smooth sweeping gesture around the keyboard.  This time, though, it was detecting finger-lifts when I was still touching the screen, and the path it showed as where I was moving my finger looked like I'd had way too much caffeine.

Now admittedly, I was not using the charger that came with the phone, but it was the Motorola charger from my first Droid.  That's the charger that I usually have in my backpack, and I have actually had occasion to look at the 5V coming out of it with an oscilloscope.  It very clean and well regulated, even under load, especially compared to many other third-party chargers.  On a hunch, though, I unplugged the charger, and suddenly the keyboard worked fine again.  This may merit some further laboratory investigation, and it might provide good justification for building a controllable noise injection circuit...

1 comment:

Blues said...

I actually had the same problem on my old Motorola Droid. I didn't have the Razr though. Mine was either first or second generation. That phone recently went boom so I replaced it with the Droid Bionic, still Motorola. No more super sensitivity while charging. I have used a variety of chargers on both phones. The sensitivity was constant while charging on the old phone no matter what charger was used. It was quite a pain. I hope you solve it.