8x8 bi colour display with 74HC595N

Hi there guys.
I have an 8x8 bi colour display that i was hoping to play with, but using just one colour used EVERY pin on the 'duino (as im sure you already know)
its this one:
http://www.oomlout.co.uk/-p-233.html

the datasheet i got with the unit suggests "use a shift register, like one of these"

so for a couple of quid i bought a pack of 74HC595N shift registers.

http://www.oomlout.co.uk/shift-registers-74hc595-x5-p-191.html
these specifically.

Now...
My theory is to use three SRs. One for the common cathode, one for green and one for red.

but the interwebs suggests (in places) that I could burn out the chips if I run all the LEDs on one row at the same time for example. In other places people report doing it with no issues.
can I? or a more productive question, how do i work it out?#

thanks! Me

OllyR:
but the interwebs suggests (in places) that I could burn out the chips if I run all the LEDs on one row at the same time for example. In other places people report doing it with no issues.
can I? or a more productive question, how do i work it out?#

The 595 can take about 20mA per pin, but only about 70mA for the entire chip.

ie. You can do 20mA on three pins, 10mA on seven pins, etc., so long as the sum of all pins is less than 70mA.

If you to run 8 LEDs simultaneously you have to limit them to 8.75mA each (or less).

If you want more current you'll have to add external transistors to drive them or use a different chip. LEDs are tricky beasts to light up properly so your best bet is to get chips which are designed to drive them, eg. TLC5916, TLC5925, etc. The other massive advantage of using driver chips for displays is that you have a much better chance of getting all the LEDs to be the same brightness than if you're using current-limiting resistors.

There's one other possibility but it's a bit horrible: Stack one 595 on top of another and solder all the legs together. You'll get a 'chip' which can handle twice the current. You can run your LEDs at 16mA and stay within the limits.

that’s great fungus.

really well explained. I get it now. thank you.

I actually have 6 SRs, is it fair to presume wiring them up in parallel, rather than physically piggy backing will have the same effect?

I have not decided for sure what i want to do with this display to be honest, so if i write into my sketch that no more than three* LEDs a row/column can be lit up, it effectively protects the hardware? This wouldn’t be a problem if I were to write a pong sketch (with a paddle of 3 pixels max)

*i will look up the data sheet for the display

OllyR:
that’s great fungus.

really well explained. I get it now. thank you.

I actually have 6 SRs, is it fair to presume wiring them up in parallel, rather than physically piggy backing will have the same effect?

So long as the wiring is equivalent, yes.

OllyR:
I have not decided for sure what i want to do with this display to be honest, so if i write into my sketch that no more than three* LEDs a row/column can be lit up, it effectively protects the hardware? This wouldn’t be a problem if I were to write a pong sketch (with a paddle of 3 pixels max)

*i will look up the data sheet for the display

Without knowing more about the display it's hard to say. The first thing you need to know is how is the LED current controlled?

You might find this page helpful in explaining the fundamentals of driving a matrix.
http://www.thebox.myzen.co.uk/Workshop/LED_Matrix.html