I am trying to figure out how to drive 64 LEDS with 16 microprocessor
I/Os.

I understand I can tie all the cathodes tied together for each row and
then drive each seperate column with transistor. The transistors
can be turned on and off by the microprocessor I/O pins sourcing (20ma max).

But an I/O pin can sink only 20 ma max and only 30ma max for each group of
8. Since 8 LEDS may be on at any one time that can be 160+ ma.

What would I use to supply the ground for the common cathode row lines?

Software guy trying to do hardware.

Thanks for any help.
Jerry Donaldson

 

You never drive devices directly with a uC I/O pin. Anything that fails means the uC gets fried, too. Use some device on the other side of a resistor like a logic level FET or a Darlington transistor to handle the current.

How are the LED's to be arranged? And are multiple ones going to be on?

 

2N7000 are N-channel MOSFETs that can work at logic level. They're available in a TO-92 case, just like transistors. You can drive the gates from your uC using 220 Ohm resistors, ground the source, and use the drain to sink current from the LEDs.

You might also investigate Charlieplexing.

 

you dont have to have all the LED's running at the same time - make each one flash fast enough so you cant see them flashing.

 

Hello,

Maxim has chips that can drive an 8 X 8 led matrix.
The data is send to the chip using serial data.
http://datasheets.maxim-ic.com/en/ds/MAX7219-MAX7221.pdf

Greetings,
Bertus