aduncan@rhea.trl.oz.au (Allan Duncan) (01/15/90)
I have had a request for details of a circuit that I built to run
multiple monitors at a demo (it is nice to see what is on the video
projector at the same time as you face the audience - essential for
games!). Since the recipient didn't have a fax I spent an hour or two
making an ASCII version of it, and decided that the rest of the world
might benefit from it, so here it comes!
Video Buffer for Amiga range of computers
(C) Allan Duncan, freely distributable.
(23) +5V ------------------------------------
| | | |
< < 100n = |
> > | |
3K9 < 680R < # |
> > |/
| | |c
| |-----------v^v^v^--| 2N2369A
| |/ | 47R |e
| |e | |\ r (9)
|---------| 2N3640 -->to others |--v^v^v^--- out g (8)
AAZ15 V |c --------| 75R b (7)
r - |\ | <
in g -----| | | >
b < < < 150R <
> > > >
2K2 < 47R < 1K5 < |
> > > #
| | |
(21) -5V ---------------------------
|
|
(16-20) gnd --- 100n =
| |
# #
Notes:
1. Bypass capacitors are ceramic style.
2. The AAZ15 is a gold bonded germanium I have got a heap of - better small
current characteristics than Schottky - any small signal Schottky will
do, or ordinary Ge.
3. The PN3640 is a PNP, the 2N2369A NPN, small signal high speed switch or
general purpose sort of thing, NOT high beta audio
4. This will work with both A1000 and B2000 video outputs
(they're different). If ypu are only using B2000 and A500, you can
delete the input level shifting (3K9, 2K2 & AAZ15) and connect direct
to the base, and the output bias, the 1K5 on each output.
5. Two or three output stages are alright (three will need extra 4049's over
what is shown for the sync buffers - partition parallel gates as you
see fit).
6. This all fits (snuggly) into an aluminium box (4x2x1) with mounted DB23
for connecting the original DB23 going to the 1081/4, flying lead DB23
to computer, and a DB9 for the extra output, which mates with a set of
mini-coax leads to the Barco or whatever. I built two of these for our
club, along with a switch-box that selects both audio and video to the
Barco projector for a public display, so that there was continuous
action, even if a machine was loading.
Sync buffers - whether you need all three will depend on the CRTs you are
driving. The 1081/4 need only S, multisyncs usually want H & V, as do
Barco projection units (the reason for this in the first place).
+5V
|----- |\
| | | \
_ 1|100n = ----| >o---
(12) V |\| | | 11 | / 12 |
_ 4049 | \ # | |/ |
(11) H ---------------| >o------v-----< >--v^v^v^-- Local CRT
_ | 9| / 10 | | |\ | 220R (ttl load)
(10) S < |/| | | | \ |
> 8| | ----| >o---
10K < # | 14 | / 15
> | |/
| |
# | |\
| | \
>----------| >o---v--v^v^v^-- Remote CRT
| 7 | / 6 | 220R (75R load)
| |/ |
| |
| |\ |
| | \ |
>----------| >o---<
| 5 | / 4 |
| |/ |
| |
| |\ |
| | \ |
----------| >o---
3 | / 2
|/
Allan Duncan ACSnet aduncan@rhea.trl.oz
ARPA aduncan%rhea.trl.oz.au@uunet.uu.net
UUCP {uunet,hplabs,ukc}!munnari!rhea.trl.oz.au!aduncan
Telecom Research Labs, PO Box 249, Clayton, Victoria, 3168, Australia.