| DIY RGB-to-component conversion project [message #262692] |
Tue, 29 July 2014 00:19  |
scott
Messages: 4237
Registered: February 2012
Karma: 0
|
Senior Member |
|
|
This is something I've kept a lid on until now, until I had a chance to
build it and verify that it'd work:
https://dl.dropboxusercontent.com/u/75937384/IMG_20140728_20 1651970.jpg
It's a fairly straightforward adaptation of the Silicon Chip
RGB-to-component converter, for which you can find the schematic linked in
the comments here:
http://damntechnology.blogspot.com/2008/08/apple-iigs-rgb-vi deo-to-component.html
Since the IIGS's RGB video port provides +12V and -5V, I simplified the
power supply circuit by using -5V directly and getting +5V from the +12V
supply with a 78L05. A resistor and capacitor mix the composite-sync
and green signals into sync-on-green, as described here:
http://www.raphnet.net/electronique/sync-on-green/sync-on-gr een_en.php
Finally, I laid out the board with SMD components instead of through-hole.
This makes it quite a bit smaller, but it's still reasonably easy to
assemble. The resistors (all two dozen of them) and some of the capacitors
are 1206 instead of 0805. The only tricky parts to solder were the
electrolytic capacitors; tinning the pads on the board and the leads on the
parts helps somewhat.
I just did some quick testing with the IIGS I had been using in the garage
on my beer fridge; since it was running without a hard drive, the sample
image here is just something I knocked together at the BASIC prompt. It
shows 80-column text and the Lo-Res color palette...going from screen to
camera may have altered the colors somewhat, but color rendition appeared
good to me:
https://dl.dropboxusercontent.com/u/75937384/IMG_20140728_20 1530904.jpg
One thing I noticed was that not every display on hand worked optimally. I
tried first with a Samsung SyncMaster 215TW, as that's the monitor my other
computers are currently using. I'd swear I had my stealth GS (ROM 01
motherboard in a IIe case) connected from its composite input to the
monitor's component Y input previously with good results, but with the other
IIGS (a ROM 3) and my new adapter, the first line was cut off at the top. I
next tried a 30" "Element" TV (what EEVBlog's Dave Jones might call a "one
hung low" brand) I had picked up cheap at the last Black Friday. It
wouldn't display anything at all...said "Not Support" [sic]. It said the
same when I drove the Y input with composite video, so maybe it doesn't like
480i video or it's extra fussy about timing. The screenshot above was taken
in the living room from a Toshiba 55G300U; the usable screen area was
approximately centered on the screen. I suspect this would work best with a
CRT TV with component input that you might already have on hand or can maybe
pick up cheap at a thrift shop, but you might get acceptable quality from an
LCD as well...the merits and demerits of Apple II video on LCDs have long
since been debated here at length.
Now for the "DIY" part of "DIY RGB-to-component conversion project:" this is
an open-hardware project. :-) Schematic capture and board layout were done
with Upverter:
https://upverter.com/salfter/365dcb155a88fcf1/rgb2component/
I sent the appropriate files to OSH Park to have some boards made. You can
order three from them for about $30, shipped:
https://oshpark.com/shared_projects/zc9OFKTW
I also have two bare boards left that I could let go for maybe $11 each,
shipped within the US, or $10 plus actual shipping to send elsewhere
(shouldn't be too much).
An orderable BOM is up at Digi-Key:
https://www.digikey.com/classic/registereduser/bombillofmate rials.aspx?path=1&exist=1&id=1817906
With shipping, parts cost me a little under $16.
I don't think I'd want to offer an assembly service until I get a
toaster-oven reflow setup in place...have the toaster oven, but need a
controller. I hand-soldered this board, and it took maybe 60-90 minutes.
A service such as Small Batch Assembly might be feasible for getting a few
boards made, but I think I'd need to tweak the design a bit before sending
it to them; while this layout includes fiducials, they're in the wrong place
and are probably too small. If you're willing to do your own assembly,
though, you could get one of these up and running at a fairly low cost.
_/_
/ v \ Scott Alfter (remove the obvious to send mail)
(IIGS( http://alfter.us/ Top-posting!
\_^_/ >What's the most annoying thing on Usenet?
|
|
|
|
|
|
Members
Search
Help
Register
Login
Home
