On Wed, Mar 17, 2004 at 11:35:00PM +0200, Andre Miller wrote:
> Thanks Byron,
>
> I read your other post, very informative!

No problem.

>
> What I have done in the meantime is change the algorithm as you and others
> have suggested to get rid of 'ghosting'. It actually helped quite a bit to
> increase the contrast. I didn't even realise it was ghosting till I took a
> closer look at the 'off' segments.

It definitely happens.

>
> Unfortunately I had already built a proto/dev board without the display
> driver. But if I were to build a new one I will definitely look into using
> the method you suggested. Although I guess I could just put the driver
> between that board and my PIC.

Correct. That would be the right place for it to go.

>
> One question though (I guess I can just go read this in the 7445 Datasheet!)
> the driver presumably has a fixed number of 'shapes' it can display, say,
> 0-9, a-f. I wouldn't be able to make custom shapes, or use it to drive the
> decimal point, right?

You missed the point a bit. The 7445 is a 1 of 10 BCD decoder. So you put in
a 4 bit BCD number from 0-9 and the part drives one (and only one) of 10
outputs low with up to 80 ma of sink current.

So by connecting 8 of the outputs to the 8 cathodes of the display you can
select each one of the segments, but only one at a time.

So it isn't like a 7447 or 7448 which translates a 4 bit value into a 7 segment
translation. So to answer your questions:

1) No it doesn't have a fixed number of shapes.
2) It can display 0-9 and a-f
3) You can make custom shapes.
4) And you can drive the DP of any display.

In addition you'll have two loose outputs that you can repurpose say for
an individual LED or somesuch.

If it turns out you don't need those extra two outputs then you can get away
with 3 input pins into the 7445 and still drive all seven segments + DP.

BAJ

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