Sometimes I just get bored and decide to tear cheap stuff apart to see if I can learn anything interesting from them. You would be surprised at the tricks you can pick up by ripping up a crappy little widget and dicking around with it. Here is today's Design Toolbox Trick O' The Day that caught me unaware (or if I did know this trick once I have forgotten it, which likely happens a lot).
I took a multifunction desk clock I got for free at a strip club, and decided to play with the LCD. I knew that you can strip some of the plasticky sheet materials off many LCDs and make them fairly transparent, something people have been exploiting lately to turn old 15" LCD panels and discarded overhead projectors into ghetto video projectors. I vaguely remember reading that you had to be careful what you pull off the LCD glass, because removal of one or more polarizers would render the LCD's display effectively invisible. I won't go into the physics of light, but suffice to say that the polarizers are absolutely essential for normal operation of typical LCDs (Google it if you wanna know more). I wasn't sure which layers of plasticky crap I needed on this multifunction calculator, so I just started peeling away and peering through the panel after each layer came off. The first layer was the most obvious; the thick, opaque reflector that allowed light to enter the front of the display and reflect off to "backlight" the characters in normal ambient light. Once that came off I had an LCD I could see through, although the adhesive used on the diffuser left some crud behind. I ended up removing both the front and back polarizers as well, and rediscovered the fact that this made a basically clear display with characters you couldn't see.
Now, for the cool part.
As I was reapplying polarizers, I found that just one polarizer was insufficient and it really does require both of them to polarize the light and show up the LCD characters. I put the front one on the way I thought it had come off, but when I put the back one on I got a surprise.
As you can see below the friggin' display INVERTED! TOO F'ING KEWL!
I'll break it down. Below we see the front polarizer attached, and I am holding the back polarizer in place in the original orientation. Looks normal, right?
Below you see me pull the back polarizer up a little, so you can see how the display is almost entirely transparent without it in place.
This alone is kinda cool, but the next discovery was cooler. If you take the back polarizer and turn it around 180 degrees you effectively invert the LCD! Below I show it partially lifted up to show the effect and necessity of the polarizer.
Here is a illustration of HOW I flipped the back polarizer, because the exact orientation of the polarizer is critical to the effect.
Obvious applications for this would be to turn an LCD into a light valve for rear illumination or projection, or just giving a tired old wall clock a l33t all-black look. If you do anything cool as a result of learning this trick please let me know!
