The Tiny 80x25 PC Display and Others


Small CRT's (3" or less) are aplenty if you know where to look.  The most common is an old camcorder viewfinder, another is the classic sony watchman.




The resolution of these small CRT's are nearly the same as larger TVs.  They have good pixel density/ dot resolution for their size. But can they deal with an 80x24 terminal, 640x240, or 640x480 image?  
An 80 column terminal is important as it is the default for most DOS and Linux console text applications, as well as the BIOS.   

Viewfinder Hack

Before I tested the terminal console, I was skeptical as images from other viewfinder projects on the web were very blurry.  The screen is literally the size of a postage stamp, so I thought the dot size would be too large for any detail.   But the results were surprisingly clear.  The limiting factor was mostly my eye's inability to see the detail of the micron sized fonts.   But the screen could be easily enlarged with a magnifying glass lens, as the native image was not noisy or distorted.   Another factor was my digital camera did not agree with the tiny screen, a lot of trial and error with manual focus and shutter speed was required.

These images are from a JVC VF-1900U I picked up on ebay for $17 shipped, made in 1982.  There were no specs/schematics for it, but the pinouts were not that hard to figure out.  The composite video input was easy to find (it was the only wire shielded) and there were markings for the 12v on the PCB.   The video input was generated directly from the VGA card and converted to composite mono video via just a few resistors.  See my Linux on Obsolete Display's Project Page for more info about this.

         


         


         
 
The image is inverted horizontally on the CRT, but can be corrected by reversing the horizontal deflection yoke wires.   I left it alone as I will probably use the viewfinder case and builtin mirror later on.

Watchman Screen

It's an FD-20A, made in 1984. This one has composite video input, so no hacking was needed. Just a wire.

         


         


It doesnt look that way, but the fonts are more clear on the watchman. However the geometry is slightly off (the yoke needs to be adjusted a little to correct the tilt). These CRT's are unique in that they have a significant curve to them, which makes the image appear to bend instead of just tilt.

CRT TV Car Stereo?

Such a thing existed. They show up on ebay from time to time. All the same model but different brand names. Pretty rare still. TV looks about the same as a viewfinder CRT.



LCD High Res and Small Size

For an LCD display, the words high resolution, small size, and low cost are almost mutually exclusive.  Only recently did samsung invent a three inch LCD capable of 640x480 color.
http://hardware.slashdot.org/article.pl?sid=06/08/12/2017229

However, there's plenty of small surplus low res color lcd's out there for cheap.  One way to boost the resolution of an LCD (at the expense of color) is subpixel rendering, in which each color subpixel is treated as a monochrome pixel.  This effectively multiplies the horizontal resolution by 3.  Here's an 80 column console on a gameboy advance screen using 3x8 subpixel fonts:
(via http://dynastab.drunkencoders.com/Projects/DSSubPixelClass/dssubpixel.jpg)



http://en.wikipedia.org/wiki/Subpixel_rendering

Other Links

http://www.penders.cwc.net/otmonotube.html - the monochrome tube
http://www.electronixandmore.com/project/pongman/  - stuffing a pong game into a classic watchman
http://www.tubehobby.com - russian made small crt's for sale

http://www.flickr.com/photos/ironleg/tags/tinycrt/ - viewfinder CRT mod for DVD

http://www.users.qwest.net/~ptaylor/Electronics/TinyCRT1.jpg
http://www.users.qwest.net/~ptaylor/Electronics/TinyCRT2.jpg
http://www.users.qwest.net/~ptaylor/Electronics/TinyCRT3.jpg

Q: How about building a small crt projector?
A: It might work, however viewfinder CRT's are not that bright.
   A very small screen projector, say 5" or less, in a dark room
   would probably be all that you could do.



Bryan Chafy
bchafy@ccs.neu.edu
8/30/06