How to switch 8 lines

bytor95

Hi,

I've been building a tide calculator and plan on showing the present tide height and the next high/low height using a 8x8 LED matrix (see attached photo).

I'm using a MAX7219 controller so I'm only able to show either red LED's or green because the 8 lines go to the red (or green) lines and the 8 other lines out of the MAX7219 go to the common cathode lines.

Now to make the display more interesting, all I'm really looking for is:

Tide going high (Show all Green)
Tide going low (Show all Red)

Is there a chip (like a seperate CMOS chip) that would "switch" the 8 anode contacts between 8 green LED's and 8 red LED's? I was hoping the basic stamp can just use one more pin to achieve this:

"0" = Green
"1" = Red

I hope I explained it right.

Thanks in advance!

Engin

Post Edited (bytor95) : 3/19/2007 7:49:30 PM GMT

T Chap

You could use 8 addressable I2C 8 or 16 bit i/o expanders to get 8*16 or 8*8 LED sinking capability. PCF8574 or PCF8575 are some that are easy to use. Does the Stamp already have dedicated I2C pins? Otherwise you would need 2 pins SCL and SDA.

bytor95

Originator,

It seemed like you replied to my question before I hit the submit button, thanks!

I'm using the BS2SX so I don't think I have the dedicated I2C pins.

Engin

Mike Green

You could use 4 quad optocouplers, 2 for red and 2 for green, and wire the LEDs in series/parallel (2 in series, 2 series chains in parallel). This way, you could switch them with an I/O current of maybe 20-30ma total for a set of 8. This assumes that you're using 2 I/O pins, one for red and one for green. You could cut this down by using some additional transistors to turn on one or the other set.

bytor95

Thanks Mike,

I'll look into the optocoupler method right now. I can tolerate using two I/O pins so that may be a great solution. Thank you very much.

Engin

bytor95

Mike,

When you get a chance, can you recommend a particular quad optocoupler? I've never used them before.

Thanks again,

Engin

Mike Green

I just Googled "quad optocoupler" and got www.vishay.com/docs/83652/83652.pdf which looks reasonable. You could also check the on-line catalogs of dealers like Jameco, DigiKey, and Mouser and they would have links to datasheets. This is a pretty basic part these days.

bytor95

Mike,

I just read through the one you linked and now I understand. I think that would work very intuitively.

Thanks,

Engin