Open hardware AV to digital conversion

From: Marko Mäkelä <>
Date: Sat, 3 Jan 2015 23:17:16 +0200
Message-ID: <20150103211716.GC1361@x60s>
Hi all,

As the CRT screens with analog video input are being replaced with flat 
panels that take digital signals such as HDMI, it would seem to make 
sense to design a converter based on open hardware.

Before you exclaim that such converters exist or that some screens can 
accept analog video from the C64, here are two counterexamples.

First example: About a dozen years ago, I tried to be future-proof and 
bought a cheap Chinese converter that outputs analog VGA (which is now 
gone). The VGA output signal is so bad quality that my current flat 
panel screen refuses to display it. It only works with a CRT VGA 
monitor, and even then in a very noisy way. I would expect currently 
available analog-to-HDMI converters to be a hit-or-miss, it either 
works, does not work, or works badly. I would guess that HDMI is here to 
stay for a while, being based on DVI and DisplayPort, and the standard 
being updated constantly.

Second example: Some flat screens are picky and do not display anything.  
Here is an example of that:
Another example is my TV, which refuses to display a picture from my 
NTSC Vic-20 board, and refuses to support separated luma and chroma (Y/C 
aka S-video).

I see a few possible approaches to this problem. Maybe the trickiest one 
would be to adjust the signal in the analog domain, so that any 
equipment would accept it. This would be tricky, because most Commodore 
home computers do not output properly interlaced video. The NTSC VIC-I 
chip is the only known exception to me: an interlaced mode can be 
enabled on it.

The most future-proof way might be to use a generic A/D converter and a 
fast enough FPGA. A more practical way could be to use a special video 
A/D converter chip, such as this one:

This chip is used on the MilkyMist One:
It is open hardware, with FPGA and microcontroller code available at and the schematic diagrams etc. at 
the following locations:

Does anyone happen to have experience of such A/D converter chips, or 
connecting Commodore hardware to the video inputs of the MilkyMist One?

The ADV7181C claims to support almost anything: PAL, SECAM, NTSC, SCART 
Fast-blank RGB, and some stuff in the VBI, such as wide-screen 
signalling and teletext (Ceefax), and various versions of the 
MacroVision protection. The challenge would be to capture the output 
into a frame buffer and output it via HDMI. We would also require a 
separate A/D converter for the audio. A bonus would be to make it so 
low-power that it would work with the small power supply that is 
available on the HDMI jack.


       Message was sent through the cbm-hackers mailing list
Received on 2015-01-03 22:00:03

Archive generated by hypermail 2.2.0.