Date   : Mon, 17 Jun 1996 17:25:51 +0100
From   : "steve" <steve@...>
Subject: Hornby Zero-1 again

As no-one replied to my previous query, I assume no-one is familiar with
the device.  I am sure that if I explain a little about it, someone is
sure to be able to help :-)

I have a few technical docs from Hornby, and they suggest that the easiest
way to interface to a computer would be simply to put reed relays in
parallel with the switches on the controller.  The switches consist of:

1. A keypad consisting of 17 non-latching push-to-make switches
2. A SPST switch to control forward/reverse
3. A slider switch for the speed control - it has one 'input' and four
'outputs' .  It uses 'Gray' code to generate 15 speed values from the 4
outputs (all 'off' is not used).

So, it seems to me that one approach is to get 22 reed relays, and arrange
for the first 18 (1 and 2 above) to be activated momentarily so simulate
key presses, and the remaining 4 for the slider, one or more of which will
be closed at any one time.

Does all this sound sensible, and if so what other hardware would I need
to interface it all to the Beeb?  One thought that does occur to me is -
is it OK for reed relays to be closed for long periods of time?

Any suggestions gratefully received.
-- 
Steve Loft, Doncaster, UK.