On Thursday 14 June 2007 01:55, Forrest W Christian wrote:
> PicDude wrote:
> > Is there any clever way to check for opens?  Is
> >there any clever way to check if the LED's actually light up (by checking
> >their voltage drop), but keeping in mind that I don't have any spare
> > I/O's.
>
> Depends on how they are wired, but remember that some of the ports on
> the PIC have weak pullups which could be used to determine if they are
> connected to ground, by switching the port to input with weak pullup and
> see which of the pins are low (connected to ground).   (Think wired-or).
>
> -forrest


The LEDs are multiplexed -- 3 RA lines go to transistors/fets to switch (to 
ground) the cathodes of the LEDs as 3 columns.  All RC lines and some RB 
lines go to the anodes of the LEDs (the rows).

Because of the transistors, I can't see a way to switch the rows and detect 
from the columns.

Because all rows are connected to the anodes, trying to switch a row and read 
from any other row will go thru 2 LEDs -- one in the forward direction and 
one in the reverse direction, so there'll be no current flow.

If I switch a column, it will affect all rows, so I can't gather much info 
from that.

But that's all in-the-box thinking.  Anyone have an out-of-the-box idea?
And btw, I really don't care much for the over-used phrase "out of the 
box". :-(

Cheers,
-Neil.
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