Why don't I see any examples or tutorials using a bunch of PNP transistors (differences to MOSFETS?) between the shift register and the LEDs to handle the current?
This will be a single color matrix with no dimming for clarification.
That's 8x20mA sourced on a single pin (the walking bit), and 20mA sinking on each column.
If those were connected straight to the arduino,
No it is the walking bit that needs the help in sourcing or sinking the current. So 20mA sinking is fine but 8X20mA sourcing needs extra help.
Technically, this design should be doing damage to something Im unclear on weather its the LEDs or microcontriller at risk, but I've been running them over a month, without failure, and no appreciable differences in brightness or color, or speed.
20mA on 8 pins is also too much.
Quote20mA on 8 pins is also too much.It isn't too much unless you are building for NASA.In that case, you can add a swich (npn/pnp, depending on your design) on the 595's output.
At 20ma/pin, it will outlast all of us, by a few multiples.
If that's true,
QuoteIf that's true,You can easily try it.
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