25 May
2005
25 May
'05
5:14 p.m.
Subject: Re: neon tube memories
From: ard at p850ug1.demon.co.uk (Tony Duell)
Date: Thu, 26 May 2005 00:38:52 +0100 (BST)
To: cctalk at classiccmp.org
Only takes 4bits to count to 10. Though it could be a switch tail
ring counter.
Unless someone has som ehard data on them being
used "digitally"
I'd assume the HP counter use was simply as generic, non-switching
circuit elements.
The HP5245 counter certainly used neons as memory elements -- I have the
instrument and the service manual which has a section on the operation of
the counter module.
Each counter module contains 8 transistors wired as 4 bistables. Diode
steering is added to make it count either in 1242 BCD code or 1248 (the
latter being one of the options available for the instrument).
The collectors of the transistors go to the neons via resistor (and
diode?) networks. By varying the voltage on one of the lines you can
transfer the state of the counter to the 8 neons and latch it there.
The neons are mounted in a plastic block with a thick-film circuit on
top. The thich film elements are CdS photoresistors arranged in a decoder
tree which directly drives a nizie tube.
Quite a hack to get a counter, latch and display driver in just 8
transistors! A write-only
neon memory would still make a nice addressable
display!
Somewhere I have a neon display which seems to be a dot-matix unit (7 dots
high by perhaps 100 long) with transfer electrodes like a Dekatron tube.
You apply 7 'bits' to the right hand column, then toggle the transfer
electrodes appropriately and all the dots move left one column. Repeat to
built up the pattern you want in the display.
-tony