25 May
2005
25 May
'05
7:38 p.m.
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