OK, strobe it, -- got it...I didn't realize you had to do that
or even that you could with LED's....at any rate, I don't think
my 4mhz 16f84  is going to do too much heavy lifting here.....

Thanks very much, I'll check back in a while, after I get going
a little better.....



----- Original Message -----
From: "Jinx" <joecolquitt@CLEAR.NET.NZ>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, August 23, 2001 6:05 PM
Subject: Re: [ot]: dot matrix display question


> > what easy trick am I missing here....
>
> I should clarify - unless you have control over each of the
> 40 LEDs in the matrix individually (ie each LED has its
> own personal switch), it is not possible to display all possible
> patterns statically. Shift registers are used to significantly
> reduce the hardware but the downside is that s/w has to
> be more complex (well, perhaps not necessarily) because
> the display now has to be strobed
>
> What you need to do is start at the top row and strobe
> downwards. But you can have the display anyway around
> you want - rows/columns, columns/rows, tomato/tomato -
> you can strobe top to bottom, bottom to top, left to right,
> right to left. Just pick one
>
> Using my schematic as an example, say you've got a shift
> register controlling the Row Select Darlingtons on the left and
> a shift register to control the column transistors at the bottom
>
> You load the Row shift register with 0000 0001 to enable
> Row1 and Row1 only. Then you load the Column shift register
> with the pattern for Row1, say 0100 0011. LEDs 2,7 & 8 will
> light. You hold that for as long as you want (depending on
> taste/LEDs/electrical stresses etc). Then load the Row SR
> with 0000 0010 to enable Row2 and Row2 only. Send the
> Row2 pattern data to the Column SR and hold. Note, that
> in the instant the selected row pattern is showing, all other
> lines are actually blank, although to our eyes, because of
> persistence of vision, they may not appear so. It's just like a
> TV scan, which is where the timing becomes important.
>
> Depending on the installation site, there may be advantages to
> using other than red. Our eyes are more sensitive to green
> (which is why night-vision equipment is green). Although things
> like fire engines are traditionally red (perhaps to incite a sense
> of urgency), yellow is a more noticeable colour against most
> normal backgrounds and yellow is favoured for emergency
> vehicles (ambulances - white & yellow stripes). However, red
> LEDs are generally the cheapest and least power-hungry
>
> --
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