life2.mp4
Conway's Game of Life, for the Raspberry Pi Pico, with Composite Video output using an R2R resistor DAC. Resolution of the 'universe' is 512x384; the speed is approximately 30 generations/second. Wiki for Multum in Parvo
A modified version of pico-composite8.
Uses the same DAC as pico-composite8, but only the top four bits are required
The input impedance of the Composite Monitor is 75Ω; the output impedance of the R2R ladder is R. In order to get 1V across a 75Ω load with a 3.3V source, R needs to be 2.3 * 75 = 172.5Ω. Closest 'standard' values are 180Ω/360Ω.
Unfortunately using those values doesn't work for 8-bits. The values are low enough that the internal resistance on the Pico GPIO pins becomes important, and causes visible errors on the 7- and 8-bit. Measuring the voltage drop on the pins gives a calculated series resistance of about 40Ω, so you will need to reduce the 2R value by that much to compensate. I used two 160Ω resistors in series:
The R2R DAC will draw about 19mA total from the Pico when all the bits are '1', with a maximum of 6.5mA on any single pin. Here's the simulation: R2R DAC Simulation
Seed patterns can be downloaded from LifeWiki.
Save the plaintext pattern file to disk and run scripts/mkLife.pl name.cells. Include the resulting name.h file in cvideo.c (line 159) and rebuild the executable.
On some program starts, the Vertical Interlace is 'out of phase' with the monitor - the interlace lines offset in the wrong directions. Plugging/un-plugging the video cable several times clears it up. Don't know why it does that.
Any ideas, let me know...