Firstly, I'd like to thank all the people who've help me out so far that contributed to the "300 mA" thread.
I'm doing an embedded systems project for college, I'm a 3rd year doing Electronic Engineering. It's a Connect4 game consisting of 42 LEDs (6 rows, 7 columns). Each LED can be either Red, Green or Off.
At the end of this post, I have a link to a PDF of the current schematic, but please read my description before opening it.
I have two 8-Bit shift registers to decide which column is currently being lit. When flashing a column, I have to flash the reds, then flash the greens, because if I flash a column with both red and green at the same time then there'll be a path from 5 V to 0 V through the LED's and an entire row will light up -- this is why I've got two 8-Bit shift registers as opposed to one; the first one flashes the reds while the second one flashes greens.
You might think my shift register setup is a bit funky as regards the RC circuits but allow me to explain. The purpose of the RC circuit which feeds into the master reset of the shift registers is simply to ensure that the chip starts up will all zeros, and it will have a very fast charging time. The RC circuit that feeds into the OR gate will have a very long charging time though, about 50 ms maybe. The reason for this is as follows:
1: I apply power to the circuit, there's initially a 1 on the input to the first shift register 2: After 20 ms, the PIC will be operational, and it will clock the 1 onto the shift register 3: About 30 ms later, the RC will have charged and be dragged down to 0 V 4: The microcontroller waits about 20 ms and then begins to just clock the 1 along in an eternal loop through both shift registersWhat's the purpose of all this you might say? It's just to save me needing to take another pin from the microcontroller for the shift register input :-D I've twelve pins in all to play with in, and I have them all used up.
Anyway, my current boggle is which chip to use for the big cyan coloured square that says "Driver" in my diagram. Basically, I want to put 300 mA through each LED (with a duty cycle of one sixteenth). I don't mean to sound utterly clueless, but I really haven't picked up the knack yet for reading datasheets. A few of you kindly suggested chips to me, but when I went to read the datasheets for the chips I didn't really have a clue of whether I'd found the chip I wanted or not. Up until Thursday I didn't know what "source and sink" meant, and I was writing it as "source and sync" :-O But of course, I'm willing to learn.
My first problem to tackle though is which chip to use for the big cyan square :D
Here's the diagram:
Thanks for your time!