neon tube memories

[Tony Duell]

> 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