TV Magic! - an amazing NTSC composite video demo on the worst fucking PIC ever

   Copyright(c) 2008
   by Christopher Abad
   aempirei@gmail.com

software this requires:

   gpasm (gputils) - GNU PIC Microcontroller GP Tools
   picp - PICStart Programmer
   PICSTART Plus Programmer hardware

hardware you NEED:

   1 PIC12F675 8-bit microcontroller
   2 330 ohm resistor (R1)
   1 150 ohm resistor (R2)
   1 RCA jack
   1 7805 +5V fixed-voltage regulator
   1 12.00mhz crystal oscillator
   2 22pF capacitors (10-30pF works too) (C1)
   5-18VDC power supply

   the reason i choose to use the 7805 voltage regulator is that the I/O pins
   output a voltage relative to the Vss, and arent regulated in any way,
   which affects the voltage on the NTSC output, so regulating the input helps
   control the NTSC signal.

optional hardware for the 'im working' indicator

   1 LED (D1)
   1 1000 ohm resistor (or whatever you want) (R3)

the schematic is as follows:

         +------+              +---+
 Vss <---| 7805 |--------------|1 8|---| gnd
         +------+              |   |    (R3)   (D1)
             |   +-------------|2 7|---/\/\/\--->|---| gnd
             |   |    ___      |   |    (R1)
            ---  ++-||___||-+--|3 6|---/\/\/\--+
             -    |         |  |   |    (R2)   |
            gnd   +-)|-+-|(-+  |4 5|---/\/\/\--+---> + RCA - <---| gnd
                    C1 | C1    |   | 
                      ---      +---+
                       -
                      gnd

   pin 1 - 7805 voltage regulator output
   pin 2 - 16.00mhz crystal oscillator pin 1 and one of the C1
   pin 3 - 16.00mhz crystal oscillator pin 2 and one of the C1
   pin 5 - NTSC out LO-voltage
   pin 6 - NTSC out HI-voltage
   pin 7 - LED power indicator
   pin 8 - ground

just do:

   ./program-p12f675.sh

some debugging hints are as follows:

first and foremost, dealing with this kinda higher frequency singals, (at least
higher, relative to audio) a scope helps immensely. beyond that obvious hint.
ive noticed that newer TVs process the analog NTSC input digitally and try to do
its best to display the input, or not display it at all, so they can be
relatively picky.  if you are just getting a blue screen (or whatever color your
inputs are on your tv by default) then try replacing the R1 and R2 with some 10K
potentiometers set up as variable resistors or voltage dividers, either way
really, and then tune the nobs until you get a working TV signal. if you get a
black screen when your screen is normally blue, you are at least on the right
track. sometimes the TV is really picky about the ratios between sync voltage,
black (darkest visible) voltage, and white (brightest visible) voltage, esp.
around the VBLANK periods and the back porch of horizontal scanlines.

thanks,
aempirei