I'm not sure if I used the symbols correctly, but in this schematic, assume all the ground symbols are connected by wires and all the +5v symbols are as well. I wasn't sure about the use of the +5v symbol and whether I should attach both symbols to their sources. (Negative battery terminal and 5v pin on Arduino)
Also, the Arduino in question is the 5v Pro Mini. Fritzing didn't have a model specifically for it.
Sorry it won't work. You have no current drivers for the rows. The arduino should only be asked to suppl;y 20 to 30mA and you have all 8 LEDs supplied off the same pins.
You also have your current limiting resistors in the row, they should be in line with the pull down, so that only one LEDs current is going through each resistor.
Are you going to multiplex them backwards, if so you might get away with it. By that I mean a walking one on the pull down drivers.
When you say the arduino should only be asked to supply 20 to 30mA, you mean per pin, right?
I think you're assuming I intend to turn on all the leds in one row at a time, which would draw current for all 8 leds from one pin.
But what I actually intend to do here is turn on all the leds in one column at a time. I've simply turned the matrix on its side, because I wanted 1,1 to be in the lower left corner.
If my walking one on the pull down drivers you mean pull down one of the pins on the pulldown driver at a time, yes, that is what I plan to do.
The spec sheet just says COM for that pin. Are you sure I need to connect something to that? And what should I connect, +5v?
It seems odd to me that I should need to connect +5v to it, since with a darlington pair, you still have only three pins to connect things to, and I've got input, output and ground connected here. Can you explain what the +5v does?
individual transistors to drive each column might be better
When you say drive, do you mean source? And do you mean instead of the ULN2803? The ULN2803 is being used to sink current here.
If you mean I should put transistors on the rows, (PNP I presume) why would that be better, or rather, why would that be neccessary?
I have to solder this circuit by hand, so I am trying to avoid lots of discreet transistors because I'll end up with a mess.
That should be pin 9, and no you don't need anything here. That is only needed if you are controlling inductive loads and then they act as fly wheel diodes.
So, now that you know I intend to light 8 leds in one column at a time, this'll work right?
I sure hope so. I just put on my parts order with mouser since they're really low on stock on those IC's. I ordered some NPN transistors just in case too, and about a thousand resistors.
