@PhiPi - looks like they have fixed that one then. Good news! I was thinking more of the 2006 demoboard http://elmicro.com/files/parallax/propdemod_schematic.pdf with a 3db cutoff of 1591hz. Since this has been fixed, just ignore my random muffled heavily filtered audio noise. Back to video..
I was wondering would it be possible to use something like an 8 bit r2r dac on vga/sound and if so would there be any improvement on images/color/capability?? I know this is probably a dumb question and the answer is no but I thought id ask, im still pretty newbish to electronics so sometimes I just gotta ask things even if I think there dumb just to verify and make sure im not missin out.
Yes I use a 64 grayscale variation of the VGA. It works beautifully with Kye's 160x120 byte-per-pixel driver. My latest variant of my (open source) und3rb3lly board has the "in between" resistors for all 8 vga output bits (P16..23). Depending on the links you can set up any kind of R2R dac, color VGA, 64 greyscale vga etc. But it can also be used to produce nice pure DDS sine waves.
For those of you with a Prop BOE, here's a workaround that will pull the RGB outputs down to acceptable levels:
I used 100-ohm 0603 resistors, as I did on the Demo Board. However, with a 75-ohm load, the peak voltage got pulled a bit too low (0.6V), which tells me that the buffer used on this board has a higher internal resistance than that of the Prop itself. Nonetheless, the image quality is much improved. Were I to do it again, I'd probably use 120-ohm resistors instead. Due to the close spacing of the through-hole pins of the rather odd DB15 connector, this turned out to be a tricky solder job. If you attempt it, be sure you have a fine-tipped iron and plenty of solder wick handy to deal with solder bridges. Also, since the board is lead-free, you should tin the affected joints first with leaded solder, then remove the excess with the wick. That will help the solder to flow more readily once you attach the resistors. And be sure to clean your work afterwards with a toothbrush dipped in isopropyl alcohol.
When testing vga driver on different monitors I realized that bad colors problem exists only with LCD monitors. On CRT all 64 colors was displayed with a good contrast between "10" and "11"
It seems these "dac" was projected in CRT times and then standards was changed.
Just a quick check-in to let you know that one of our boards (the new Propeller Proto Board) has been revised by Kevin Cook, so one of three (Propeller BOE, PPDB, and Prop Demo Board) is now done. Jessica will get to the others in due course.
Just a quick check-in to let you know that one of our boards (the new Propeller Proto Board) has been revised by Kevin Cook, so one of three (Propeller BOE, PPDB, and Prop Demo Board) is now done. Jessica will get to the others in due course.
Ken Gracey
What else is different about the "new Propeller Proto board"?
Thanks, Ken. Kevin called me yesterday to verify some resistor values, and I think he's on the right track. I'm really happy with Parallax's response so far!
Here are a couple of calculations for using ResNets to minimise the space required...
VGA: 1 @ 4 x 240R, 1 @ 4 x 510R, 1 @ 4 x 130R. I think the VS will run fine with a series 510R but to be sure I am going to provide an extra 0805 in parallel just in case.
TV: 1 @ 4 x 180R, 1 @ 4 x 390R. My alternative preferred values are not readily available.
Comments
I think Browser would regard that as entirely inadequate. Can't cats hear up to 100kHz or thereabouts?
Good on you for raising the VGA resistor issues. But compressing 64 colors will be harder than 27
regards
tubular
Yes I use a 64 grayscale variation of the VGA. It works beautifully with Kye's 160x120 byte-per-pixel driver. My latest variant of my (open source) und3rb3lly board has the "in between" resistors for all 8 vga output bits (P16..23). Depending on the links you can set up any kind of R2R dac, color VGA, 64 greyscale vga etc. But it can also be used to produce nice pure DDS sine waves.
I used 100-ohm 0603 resistors, as I did on the Demo Board. However, with a 75-ohm load, the peak voltage got pulled a bit too low (0.6V), which tells me that the buffer used on this board has a higher internal resistance than that of the Prop itself. Nonetheless, the image quality is much improved. Were I to do it again, I'd probably use 120-ohm resistors instead. Due to the close spacing of the through-hole pins of the rather odd DB15 connector, this turned out to be a tricky solder job. If you attempt it, be sure you have a fine-tipped iron and plenty of solder wick handy to deal with solder bridges. Also, since the board is lead-free, you should tin the affected joints first with leaded solder, then remove the excess with the wick. That will help the solder to flow more readily once you attach the resistors. And be sure to clean your work afterwards with a toothbrush dipped in isopropyl alcohol.
-Phil
It seems these "dac" was projected in CRT times and then standards was changed.
Ken Gracey
-Phil
VGA: 1 @ 4 x 240R, 1 @ 4 x 510R, 1 @ 4 x 130R. I think the VS will run fine with a series 510R but to be sure I am going to provide an extra 0805 in parallel just in case.
TV: 1 @ 4 x 180R, 1 @ 4 x 390R. My alternative preferred values are not readily available.
Here are the calculations....