MAX7219 Ghost!

Archiver

I am running two digits with the MAX7219 and constangly get gohsting
on the second digit even if I send it a "blank" instruction (15).
Even with the blank, the second digit shows the same character as on
the first digit but much fainter (about 10%) brightness. The only
way I can eliminate the gohsting is to set the scanning to 0 (one
digit)and in that case the gohsting disappear but of course loose
control over the second digit.

Anyone has encountered this? Is there a solution? I am sure there
is...

PS. I followed the circuit and program that exist in Scott Edward's
book to the letter.

Many thanks...

Al

Archiver

At 07:38 PM 6/10/02 +0000, brownstamp wrote:
>I am running two digits with the MAX7219 and constangly get gohsting
>on the second digit even if I send it a "blank" instruction (15).
>Even with the blank, the second digit shows the same character as on
>the first digit but much fainter (about 10%) brightness. The only
>way I can eliminate the gohsting is to set the scanning to 0 (one
>digit)and in that case the gohsting disappear but of course loose
>control over the second digit.

It sounds as if your scanning frequency is too high or your LEDs have too
much capacitance. Does the MAX chip have anything to control inter-digit
blank time? If it does, try increasing that.

The problem you are having is caused by stored charge in the output drivers
of the MAX chip and the LEDs themselves. The cure is to reduce the scan
frequency and to increase the dead time between each digit as it is scanned
(inter-digit blank time).

dwayne



--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax

Celebrating 18 years of Engineering Innovation (1984 - 2002)
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Archiver

This sounds logical. But how do I reduce the scanning frequence of
the MAX?

Al


--- In basicstamps@y..., Dwayne Reid <dwayner@p...> wrote:
> At 07:38 PM 6/10/02 +0000, brownstamp wrote:
> >I am running two digits with the MAX7219 and constangly get
gohsting
> >on the second digit even if I send it a "blank" instruction (15).
> >Even with the blank, the second digit shows the same character as
on
> >the first digit but much fainter (about 10%) brightness. The only
> >way I can eliminate the gohsting is to set the scanning to 0 (one
> >digit)and in that case the gohsting disappear but of course loose
> >control over the second digit.
>
> It sounds as if your scanning frequency is too high or your LEDs
have too
> much capacitance. Does the MAX chip have anything to control
inter-digit
> blank time? If it does, try increasing that.
>
> The problem you are having is caused by stored charge in the
output drivers
> of the MAX chip and the LEDs themselves. The cure is to reduce
the scan
> frequency and to increase the dead time between each digit as it
is scanned
> (inter-digit blank time).
>
> dwayne
>
>
>
> --
> Dwayne Reid <dwayner@p...>
> Trinity Electronics Systems Ltd Edmonton, AB, CANADA
> (780) 489-3199 voice (780) 487-6397 fax
>
> Celebrating 18 years of Engineering Innovation (1984 - 2002)
> .-. .-. .-. .-. .-. .-. .-. .-. .-. .-
> `-' `-' `-' `-' `-' `-' `-' `-' `-'
> Do NOT send unsolicited commercial email to this email address.
> This message neither grants consent to receive unsolicited
> commercial email nor is intended to solicit commercial email.