> This will be so fast that the leds won't even visibly light up
> before data has passed them.  I have tested this with a
> 32x8 array and 4 pinwheels rotating on the display.  Updates
> then took 1.28 us and the led's were lidt for almost 125 ms
> giving 8 fps.  (For this I used the image stored in ram, and
> just fed the display a new block every 125'th ms.  (To test
> 25 MHz shift frequency)
> Looked kinda cool :)

Sounds kinda cool too !!

Your point about the refresh rate is what I was a alluding to
about timing headroom. Give the micro everything to do
and the LED off/on ration will suffer, causing flicker. One
point about drivng LEDs with pulses though - most have
best output efficiency at a particular current. Too little and
they won't be their brightest, too much and you're wasting
power or unnecessarily stressing components. Some fore-
thought is needed to get the best out of the whole display.
Even the choice of switching transistors will affect the light
level, for example high-current Zetex ZTX types will switch
pulses far better than the ubiquitous BC548 and yet they
are smaller and not much more expensive (ZTX are my
choice for IR transmission too, vastly superior)

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu