|Written by AnubisTTP on 2008-01-05
While at a hamfest several years ago, I bought a badly crushed camcorder from someone's scrap box for a dollar. The camera used a minuscule round CRT in its viewfinder, the viewing surface only a half inch in diameter. As soon as I saw that CRT, I knew I had to build something out of it. The question was, what?
After some experimentation, I discovered that one of the input pins on the CRT's driver board would accept standard NTSC video signals. In researching the pinouts I found Jon's Electonics Projects, a site on which the author gave a brief description of how he hooked an old camera viewfinder CRT up to a PIC chip programmed with some readily available Tetris code that would generate an NTSC signal as the output. I decided this was a fine idea, and that I would have to build one of my own.
The Tetris device that Jon built uses a transparent plastic case that completely encloses and protects the tube. I decided to go with a wooden case instead of a plastic one for my own device; I figured that there was no way in hell anyone but an eye doctor was actually going to play the thing, with its silly, tiny screen, so I might as well put form ahead of function. Moreso, I wanted to show off the minuscule CRT, so I left the tube completely exposed on the outside of the case. The tube's socket is mounted in a flexible rubber boot, which provides some modest amount of protection from rough handling.
There are no controls on the device to move or rotate the Tetris pieces. Control is provided by a standard DB-9 Atari joystick connector, as recommended by the original programmer of the Tetris software. In retrospect, I should have added some controls to the case to move the pieces, as it is quite awkward to have to dig out that joystick every time someone wants to play a game. The device should be compatible with the Sega Genesis controller as well, but has not been tested yet.
Inside there are two PCB's buried in the snarl of wires. One contains the original CRT driver circuitry (not visible in the picture, is it is attached to the lid). The other is a custom PCB that contains the PIC chip and support circuitry for the Tetris hardware. The circuit for the Tetris hardware can be found on Rickard Gunee's site, so I will not duplicate it here. Rickard sells PCB's for his PIC chip game platform, but they are too large for this application due to the inclusion of board mount connections for two players and other such features that are necessary for the full PIC chip game experience. I made a custom stripped-down board and had it fabricated by BatchPCB, a low volume PCB supply house. The rest of the device's interior is taken up by a 9V battery for power. A barrel jack is also installed for attachment of an external power supply.
The custom printed circuit board was designed in Eagle, a popular CAD program targeted at PCB layout.