Dual Head Rainbow Video

Tapley, Mark mtapley at swri.edu
Tue Jun 28 11:46:04 CDT 2016

On Jun 27, 2016, at 4:23 PM, Rob Jarratt <robert.jarratt at ntlworld.com> wrote:

> The machine came to me with a handmade split cable. I will work out the pin
> out and post it. You need a BCC17 cable for the VR241 (BCC03 doesn't work in
> this configuration).

	Here is a repeat of a somewhat old post from this mailing list. I think applicable here, though. Hope this is useful. Not my work, I use my Rainbow with one monitor at a time, but this is on my to-do list at some point.
	Thanks to Tony Duell for the original.

Date: Wed, 1 Dec 1999 22:29:53 +0000 (GMT)
From: ard at p850ug1.demon.co.uk (Tony Duell)
To: classiccmp at u.washington.edu
Subject: Rainbow Monitor Cable
Message-ID: <m11tIG5-000IyPC at p850ug1>
Content-Type: text

I seem to remember some old posts here about using 2 monitors with the 
DEC Rainbow, or using a non-standard monitor, etc. I've just made up a 
cable which seems to allow just about every possible combination -- I'll 
stick the wiring diagrams and instructions at the end of this message. 
I've not tested it fully yet, but it certainly seems to work for all the 
combinations that I've tried.

A universal DEC Rainbow video cable

This cable allows almost all possible monitor combinations to be used 
with the Rainbow (see below).

Connections : 

Rainbow end (DA15-S)

  1 >----------+---------+-- Blue Gnd
     9 >-------O---------O-- Blue
  2 >----------+---------+-- Green Gnd
    10 >-------O---------O-- Green
  3 >----------+---------+-- Red Gnd
    11 >-------O---------O-- Red
  4 >----------+---------+-- Mono Gnd
    12 >-------O---------O-- Mono
  5 >----+
    13 >-+     +------------ Power Gnd
  6 >----------+------------ Key Gnd
    14 >-------------------- From Key
  7 >----------------------- Power 12V
    15 >-------------------- To Key
  8 >----------------------- Key 12V

  Box-mounted connectors :

  VR201 (DA15-P)

  1 o
     9 o
  2 o
    10 o
  3 o
    11 o
  4 o-----------+--------+--- Mono Gnd
    12 o--------O--------O--- Mono
  5 o-------+---------------- Power Gnd
    13 o    |
  6 o-------+---------------- Key Gnd
    14 o--------------------- From Key
  7 o------------------------ Power 12V
    15 o--------------------- To Key
  8 o------------------------ Key 12V

  Monitor BNCs : 

  ( o )--------- Red Gnd
    +----------- Red 

  ( o )--------- Green Gnd
    +----------- Green

  ( o )--------- Blue Gnd
    +----------- Blue 

  ( o )--------- Mono Gnd
    +----------- Mono 

   LK201 keyboard (RJ11-- front face view)

                |     |
          -----        -----
          |                |
          |                |
          |                |
           --  ^  ^  ^  ^--
               |  |  |  | 
 From Key -----+  |  |  +----- To Key
 Key 12V----------+  +-------- Key Gnd

Components :

DA15S socket + hood (to fit Rainbow video connector)

DA15P plug + jackposts (for VR201 connection)

4 off 75 Ohm BNC sockets (for monitor connections). You could use other 
connectors, like RCA phono, but BNC are standard.

RJ11 socket, chassis mounting (for LK201 keyboard). Chassis mounting 
sockets of this type are very hard to find. I ended up making a bracket 
to clamp a PCB-mounting one to the panel

Metal box of a suitable size to hold the above connectors (apart from the 

1m cable. At least 4 75 Ohm screened cores and 6 single wires. I used a 
'unversal SCART cable' which has 6 75 ohm screened cores (I simply 
ignored 2 of them), a 4 way screened cable (I used this for the 4 
keyboard connections) and 4 other wires (2 in parallel for each of Power 
12V and Power Gnd).

Possible monitor combinations : 
1) VR201 only
This is pretty useless, but you can connect a VR201 mono monitor using 
the DEC lead to the DA15P on the box. Connect the LK201 keyboard to 
either the VR201 or the RJ11 on the box.

2) Standard composite mono monitor
Connect monitor input to 'mono' BNC on the box. Connect LK201 to the RJ11 
on the box. This works just like a VR201, but you can use any monitor

3) VR201 and separate mono graphics monitor
Connect VR201 to DA15P. Connect LK201to either RJ11 on the box or to
VR201. Connect second (composite) monitor to the 'green' BNC. You can use
the dual monitor driver for GSX and have text on the VR201 and graphics on
the second monitor

4) Two composite mono monitors
Connect one to 'mono' BNC, other to 'green' BNC. Connect LK201 to RJ11 on 
box. Using the dual monitor driver, you get text on the first monitor and 
graphics on the second monitor

5) RGB (sync-on-green) colour monitor (e.g. VR241)
Connect monitor inputs to BNCs as follows : 
Red - Red
Green - Mono
Blue - Blue.
Connect LK201 to RJ11 on box. This gives the standard DEC color monitor 
connections giving green text and colour graphics using the colour 
monitor driver

6) RGB monitor and VR201
Connect VR201 to DA15P on box. Connect LK201 to RJ11 on box. Connect 
color monitor as follows
Red - Red
Green - Green
Blue - Blue
This gives separate text and colour graphics displays when used with the 
dual monitor driver

7) RGB monitor and composite mono monitor
Connect mono monitor input to 'mono' BNC. Connect LK201 to RJ11. Connect 
colour monitor as follows
Red - Red
Green - Green
Blue - Blue
This gives separate text and colour graphics displays when used with the 
dual monitor driver

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