Thanks for the feedback everyone - doesn't look as if it's as cut and dry as I was hoping. Looks like a longer prototyping phase is in order
leave some processor time for your atmega to actually perform some calculations yeah?
Nah, there's nothing intensive I've got to do CPU side - everything else needs updating by the minute or by the day.
Bit more power hungry this way
Yeah, just a little. I didn't mention (I'm awful at requirements analysis) that this project is hopefully going to be battery driven, but I don't think that's going to be realistic - at 20mA I'm only going to get 25 days runtime off of alkaline D-cells.
A long time ago I wrote some code that did 5bit software PWM with such a matrix. It took 50% of the cpu load.
I guess I'll start at 1bit resolution and work my way up - see how far I can get.
Following all your posts, I did start going down one of those horrific mental tangents. "Hmm, could I make a PWM pulse train generator in 74' logic... Latching shift register, feeds DAC, Sawtooth wave generator and DAC output feed into schmit trigger/comparator and use that to drive the MOSFET switch." Then i realised I'd have to to all of that for each one of my 192 output channels
. Lets not go that way.
Thinking about it some more I can add some design constraints that will give me the flexability of limiting the number of LEDS that are on at one time to a handful( <5 with error states ), so all of a sudden I'm in a different territory.
I need to think about this one... (Posting out loud here and without really thinking things through - I'll probably have a facepalm moment as soon as I've pressed post, but here goes)
2 x 74138 driving 16 MOSFET switches that act as row and column selectors deliverying V(led) (pre-LED common anode) to then simply have 3 MOSFETS switches to which all the cathodes of each colour type are linked to and then the PWM train is driven direct from the mega.
How does that sound? We can get the 8-bit resolution cycling through the lights and the limit will come as we keep adding more lights on at the same time as we may drop below 100Hz refresh rate and have some flickering come in.