On 23 May 2015 at 16:35, Chris Osborn <fozzt...@fozztexx.com> wrote: > > Are you on the CoCo mailing list? Have you seen the RGB2VGA by Luis Antoniosi > (CoCoDemus)? I know at one point he had been tinkering with making it support > composite from the Apple II. It’s semi open-source, I think there are 2 > versions and the latest version is currently all closed source. > > https://sites.google.com/site/tandycocoloco/rgb2vga
Is it me or was there a trick missed in the ADC section? > To measure a voltage signal you need to perform successive comparisons > against different > voltage levels until you find which voltage is higher. For 3-bit ADC we need > to perform 8 > comparisons. We start with the DAC in 000 (the lowest voltage) and this will > return 0 or 1 > according to the signal voltage. We concatenate all the subsequent tests to > create a > thermometer for the signal. > [...] > This will gives us the voltage of the signal, but there are errors due to > noise and voltage > fluctuation. We will never be free of them though one way to reduce the > problem is to perform > more tests, adding more bits to the DAC. Unfortunately we are on the limit of > the FPGA > clock speed. If you have 8 comparisons to spend I wonder if a modified binary chop would have been more efficient? A standard binary chop would take three comparisons, but I would have thought if you repeated each stage twice (and a third time for up to two of them if they differed), that would give you a more robust output...
