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Gents thank you for your comments.
You all have a valid point in your own way.
One thing you all overlooked that this is a chaser.
Think of a very compact 4017 counter with 24 outputs and it all makes sense.
If you have another application for this circuit in mind state your application and let's talk about it. i.e.: Light up all 24 LEDs at one time.
Now you're talking about lighting 3 LEDs at a time, one in each group of eight, with a 1/8th duty cycle. No transistors required. That's a viable design. I like it. You might get about 2.5-ma "average" current per LED which is surprisingly bright.As it is the circuit does 3/24=1/8 with 25ma LEDs, no sink transistors.
Now you're talking about lighting up to 12 LEDs at a time, up to four in each group of eight, at 50% duty cycle. No transistors required. You might get about 2.5-ma "average" current per LED which is surprisingly bright. You may perceive a difference in brightness depending on the number of LEDs lighted at one time in each group.Decrease the series resistors, and use lower mA LEDs (SMD) and you can light up all at the same time if you electrically supply it well.(LEDs of 5-7mA)
You lost me. I know about LED "pulse" or "peak" current specs'. Why are you mentioning it for this direct I/O design?Most LEDs (check your specs) can drive high current pulses for a short time. (I have 5mm LEDs that can pulse 120mA for a short duration-ms).
Your post seemed incoherent (to me). You said to consider the design as a pseudo 4017 with 24 outputs (1 LED at a time) then you talk about lighting all the LEDs. I guess I assumed this was a type of "learning exercise" better suited for a blog.The rest of the brightness issues (so minor after above changes) can be made in software to compensate.
Why are you (and Mike) saying this is not charlieplexed? It is clearly three 1x4 charlieplexed matrices.
I am not going to waste my time answering any more details on this merry-go-round.