[sdiy] Driving LEDs

[Colin Hinz]

On Mon, 22 Dec 2003, John Blacet wrote:

> OK, here's the problem:
>
> I need to drive 20 LEDs from a PIC type uC. The LEDs are on a separate
> board so I want to keep the number of interconnects small. I only need
> one LED at a time to be on. So, I seem to need a decoder with 5 lines in
> to 20 out. Most of the stuff I see is 3 to 8. Any ideas?

If you use I2C expanders you need only two lines! And there are also
dedicated I2C chips for driving LEDs (programmable blink rates --
whoohooo!!) as well.

from Philips:

PCA9552 - 16-bit I2C LED driver with programmable blink rates
PCA9551 -  8-bit I2C LED driver with programmable blink rates
PCA9532 - 16-bit I2C LED dimmer
PCA9554 -  8-bit I2C I/O port
PCA9555 - 16-bit I2C I/O port

I2C isn't unmanageable to bit-bang, even with a little PIC.

http://www.semiconductors.philips.com/buses/i2c/

- Colin Hinz
  Toronto, Canada