74LS90 replacement

[Ian Fritz]

Paul --

You brought this up before. Here is what the spec sheet says:

"When in the dot mode, there is a small amount of overlap or "fade"
(about 1 mV) between segments. This assures that at no time will all
LEDs be "OFF", and thus any ambiguous display is avoided."

So if your input steps are 1 V, then the overlap is 0.1%. Note there is
no mention of "the eye is led to think the dot is moving smoothly".

Another way of looking at it is that for a 1 kHz driving wave, the
transition times are 100 nsec.

I've used the outputs to trigger monostables driving a bank of S/H's. No
problem at all getting this to work. The transitions are actually very
crisp. They even look clean with the driving waveform running well over
20 kHZ. 

  Ian


Paul Perry wrote:
> 
> Has anyone actually done this?
> Because I think the stages do not go on and off exactly sharply, so that
> the eye is led to think the dot is moving smoothly across.
> It might still be a good thing, but you might not be getting what you
> would from a more 'precision' setup.
> Still, would be a great mod for the MadMouse!
> 
> paul perry melb aust