Light pens?

[Bjørn]

On Fri, 18 Mar 2005 16:47:14 -0800 (PST), Eric Smith <eric at brouhaha.com>  
wrote:

> Tony wrote:
>> I can tell you that although the MDA card has a light pen connector, the
>> light pen certainly doesn't work on the 5151 monitor (far too long a
>> persistance).
>
> Long persistence phospor doesn't preclude the use of a light pen, it
> just introduces some limitations on the usage model.  The DEC Type 30
> and 340 displays as used on the PDP-1 through PDP-10 use a P7 phosphor
> which has very high persistence, yet light pens were commonly used with
> them.
>
There were some tricks with LP displays. One was to generate "sensitive"  
fields with a rather dark background which was set to black for every  
second frame. The decay was shorter for very dark areas to start with, and  
to make it work with a cheap pen you just halved the refresh frequency.

-- 
-bv