At 10:00 PM 8/15/02 +0100, you wrote:
>Already burnt my first PIC (am I official now?).. hooked up +13V to pin 2
>rather than 1 by mistake..won't be doing THAT again.
>Anyway, I have a 2-digit 7-segment LED thing lying around, but it's common
>cathode (assuming cathode is +ve!).. anyway, I can't figure out how I can
>use it with a PIC - you can't set a pin to groun can you? :(

Sounds like "common anode".

Yes, it's easy to use with a PIC. You can drive it easily with 10 port pins
and a couple of BJTs, and somewhat less easily with fewer port pins. I don't
recommend trying to drive it without the BJTs, not enough current, but
I've seen it done (with poor results).

Like this will work (assuming it is CA) - that's Common Anode, not California,
Canada or Chromel-Alumel  ;-)


                    +5
                 |/ E
D0----[470R]----|       PNP eg. 2N4403, 2SA1015 etc.
                 |\
                   -----> Digit 0

(duplicate for Digit 1) 2 total

S0-----[150R]------> segment A

(duplicate for B..G, and decimal point) 8 total (you can use network(s))

Here's a data sheets for 3/4 digit displays we have:

http://www.trexon.com/leds/trexon_led_display.pdf

This kind needs less current, but same idea.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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