24-10-2019, 12:58 PM
(This post was last modified: 24-10-2019, 12:59 PM by ppppenguin.)
Frank, while I congratulate you for getting a modest PIC device to generate a testcard waveform I still think it's a hard way to do it. With modern mass storage such as SD cards so big and cheap the easy aproach is to store the whole picture as literal data and read it out with counters. The counters would typically be implemented in programmable logic but it might be possible to do them on a PIC.
Several people have taken this approach, even before the days of cheap flash. Richard Russell stored the whole PAL 8 field sequence in ordinary UV EPROMs for his test card generator.
The main advantage of this approach is that you can store any picture. It can also be 100% accurate for things like sine wave frequency gratings. Not possible with the PIC approach. Even if you store the data oversampled at 54MHz (for 625/525 systems) and are very wasteful by using conveninet binary boundaries it's still only 4M samples for a frame. (actually 2.16M, rounded up to nearest binary power). If you want 10 bit resolution then double than to 8MBytes. A very ordinary 4GB SD card will hold 512 separate frames. That's enough for over 20 seconds of animated video if you choose to use it that way.
The main job is to write some software that takes an image an prepares the data for putting on the SD card. It has to put on syncs, do PAL/NTSC encoding if needed etc. I know Karen Orton has done this. As has Grahm Davies. Probably best done by using existing image manipulation tools as far as possible.
Graham has done me a very nice 625 line Test Card C a few years back. Active picture only, no sync, 13.5MHz sampling. 601 levels. Supplied to me as a CSV file. It sits in my experimental 625 to 405 and 405 to 625 converters. It's part of the data put into a 27C040 EPROM (antique in its own right) which is then uploaded by an x51 class MPU into SDRAM. Done this way because that was the hardware I had to hand.
Several people have taken this approach, even before the days of cheap flash. Richard Russell stored the whole PAL 8 field sequence in ordinary UV EPROMs for his test card generator.
The main advantage of this approach is that you can store any picture. It can also be 100% accurate for things like sine wave frequency gratings. Not possible with the PIC approach. Even if you store the data oversampled at 54MHz (for 625/525 systems) and are very wasteful by using conveninet binary boundaries it's still only 4M samples for a frame. (actually 2.16M, rounded up to nearest binary power). If you want 10 bit resolution then double than to 8MBytes. A very ordinary 4GB SD card will hold 512 separate frames. That's enough for over 20 seconds of animated video if you choose to use it that way.
The main job is to write some software that takes an image an prepares the data for putting on the SD card. It has to put on syncs, do PAL/NTSC encoding if needed etc. I know Karen Orton has done this. As has Grahm Davies. Probably best done by using existing image manipulation tools as far as possible.
Graham has done me a very nice 625 line Test Card C a few years back. Active picture only, no sync, 13.5MHz sampling. 601 levels. Supplied to me as a CSV file. It sits in my experimental 625 to 405 and 405 to 625 converters. It's part of the data put into a 27C040 EPROM (antique in its own right) which is then uploaded by an x51 class MPU into SDRAM. Done this way because that was the hardware I had to hand.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
