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'[ot]: dot matrix display question'
2001\08\22@182137 by rad0

picon face
Hello,

thanks for all the ideas before and the help today...

for the moment I have settled on using two 8 bit shift registers cascaded to
make
a 16 bit word...to drive a 5 x 8 dot matrix display

my question today is about the dot matrix display, I am not getting the
proper
dot to light up when I bring the pins high, that I am expecting to

so either I'm not turning on the correct pins or something is not hooked up
correctly

first, how is the dot matrix supposed to work?
(I don't have the exact data sheet, but they all ought to be the same
shouldn't they?)
(I have one for another brand 5 x 8 matrix)

do you bring the pin high on the anode,
and the corresponding pin on the cathode low? this doesn't seem to work, I
have tried
doing this and then bringing the adjacent pins on the cathode high to turn
them off
and this didn't work either,  so what am I not doing or doing wrong here?

at the moment I have the matix connected directly to the output from the
shift registers, no resister, do I need on here as if I were connecting
individual
LEDs?


thanks

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2001\08\22@204937 by rad0

picon face
well, nevermind, my data sheet is incorrect/wrong

now, I just need to leran how to program....

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2001\08\22@234626 by Jinx

face picon face
> now, I just need to leran how to program....

and how to spell "leran" ;-))) Sorry

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2001\08\23@004723 by rad0

picon face
hey buddy,

so, I've figured out how to turn on the dots now,

is there a way to gain control over the dots completely?

as in 1 dot on in different rows and columns?


thanks,

no typos this time...



{Original Message removed}

2001\08\23@065321 by Jinx

face picon face
> so, I've figured out how to turn on the dots now,
>
> is there a way to gain control over the dots completely?
>
> as in 1 dot on in different rows and columns?

Here's what I'm thinking of for mine - each dot is addressable
and the rows can be extended to the the right. How you drive
the LED crosspoints is up to you. I'm considering a 74HC164
for each group of 8 columns and either a single 74HC164 for
all the rows or a 74HC164 for each 8 columns (thereby making
it possible to break the display down into 8x8 characters that
can be manipulated individually)

I've chosen Zetex transistors as they will switch high current
quickly and also have a low saturation voltage. Another
reason is that a feature I'd like to add is fading. With greater
control over the pulse width (and its integrity), fading should
be quite feasible

http://home.clear.net.nz/pages/joecolquitt/8x8led.html


> thanks,
>
> no typos this time...

Thanks for plyaing ;-))

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2001\08\23@151259 by rad0

picon face
nice schematic, Jinx....

I am using two 74hc595 , cascaded -- 8 bit shift registers, using the bottom
14 bits,
my dot matrix is a 5x 8, it has 14 pins...this works OK, but I think I am
going to use
individual transistors to juice it up also, should be inexpensive...

I have found that each individual dot can be controlled, by itself, but that
certain
pairs on the matrix cannot be turned on....is this true or am I missing
something?

I guess it is not possible to use one of these matrices the way you would
use an
8 segment display, or for individual character...this true right?

I had the notion that I would be able to find the bit pattern for a
particular dot
and then AND it with another bit pattern to turn them both on....LOL


I'm looking into other ways to power this thing, let me know your
progress...

thanks
rad0



{Quote hidden}

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2001\08\23@175922 by Jinx

face picon face
> nice schematic, Jinx....

http://home.clear.net.nz/pages/joecolquitt/0symbols.html

> I have found that each individual dot can be controlled, by itself,
> but that certain pairs on the matrix cannot be turned on....is this
> true or am I missing something?

If you have a row enabled, then any LED in a column that intersects
with that row should light if told to. Is it that when you have two LEDs
on the brightness dips so low you think they're off ? I presume the
5 x 8 matrix you have has 13 pins for rows and columns and an NC,
ie a plain LED array with no smarts. If so, then the above applies.
Any LED or combination will light if the appropriate rows and
columns are enabled

> I guess it is not possible to use one of these matrices the way
> you would use an 8 segment display, or for individual character
> ...this true right?

You should be able to display any pattern you wish to if you have
control over each individual LED

> I'm looking into other ways to power this thing, let me know your
> progress...

I'm still considering my options. I've a list of features that I want
to use (fade, wipe, scroll, dissolve etc) which can all be done
in software if I choose the right hardware. It ain't over just yet,
but the fat lady is on stage

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2001\08\23@182956 by rad0

picon face
on this 5x8

pins
9 -- 3 -- 4,11 -- 12 -- 6

for the columns

for the rows
13
8
14
10
5
1
7
2

to light up the lower left dot only,  you need to power
2 -- the row and (just 2, lights up the entire row)
to get the bottom left most dot you need to power 3, 4 or 11,
12, and 6.....OK?


now lets say you want the lower left dot and the dot that is
up one row and over one column....???  how do you get only these
two dots, without others ??

this is what I haven't yet been able to do...

when you enable the row above the bottom, the dot directly above the lower
left comes on, only this one...the rest are disabled to isolate the lower
left dot,
and when you try to enable a dot one column over and a row up, you also
get a dot on the bottom row....do you see what I mean??

what easy trick am I missing here....

thanks


> If you have a row enabled, then any LED in a column that intersects
> with that row should light if told to. Is it that when you have two LEDs
> on the brightness dips so low you think they're off ? I presume the
> 5 x 8 matrix you have has 13 pins for rows and columns and an NC,
> ie a plain LED array with no smarts. If so, then the above applies.
> Any LED or combination will light if the appropriate rows and
> columns are enabled

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2001\08\23@190627 by Jinx

face picon face
> 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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2001\08\23@194105 by rad0

picon face
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 removed}

2001\08\23@202152 by Jinx

face picon face
> OK, strobe it, -- got it...I didn't realize you had to do that

Yup, you're on to it. Didn't realise the source of your frustration.
As you've found out, trying to do it statically results in a whole
row and a whole column lighting. Which isn't much use unless
you're trying to scare vampires

You'll see the strobing in commercial units if either they're
scanned reasonable slowly (the result will be tilted characters
as the LEDs in successive rows appear to lag behind - the
fewer the number of LEDs you assign to a block, the smoother
the result) or you flit your eyes while looking. Same flashing you
see in a LED lit by AC

> or even that you could with LED's

LEDs can be pulsed extremely quickly (eg IR remote controls,
wireless data transmitters or lasers such as the ones in tag
games)

> I don't think my 4mhz 16f84 is going to do too much heavy
> lifting here.....

Nah. Apart from sending data to the shift registers and timing
the display delays it's not got much to do

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2001\08\23@204108 by rad0

picon face
> You'll see the strobing in commercial units if either they're
> scanned reasonable slowly (the result will be tilted characters
> as the LEDs in successive rows appear to lag behind - the
> fewer the number of LEDs you assign to a block, the smoother
> the result) or you flit your eyes while looking. Same flashing you
> see in a LED lit by AC

perhaps it is possible to have some LED's on completely, while strobing
only the ones needed to fill out the character or pattern......?


> > I don't think my 4mhz 16f84 is going to do too much heavy
> > lifting here.....

here I actually was wondering if a 4mhz 16F84 is fast/powerful enough to
present a good display.....now that my little experimenter set up is working
,
I have it sitting here counting up through 65K and shifting it out to
the register, to the matrix....and without the transistors it kinda dim,
in a dim room....but I also have a row of 16 single led's to check the
register pin too, I'm on led overkill here.........so maybe without this
drain...

could a darlington transistor array be used in this application?  I was
looking at
a ULQ2003A, and was wondering if that could be connected somehow...I get
the idea of how the individual transistors make the circuit, but this array
isn't
obvious to me how to hook it up....

anyway, off to tinker,
thanks for you help...


>
> Nah. Apart from sending data to the shift registers and timing
> the display delays it's not got much to do
>
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2001\08\23@213913 by Jinx

face picon face
> perhaps it is possible to have some LED's on completely,
> while strobing only the ones needed to fill out the character
> or pattern......?

Yes it is. Any LED that's on is part of a pattern

You'll see in my circuit that the 75R is lower than what you'd
expect for an LED running on 5V. This is because the LED
does not see a constant 5V, but pulses. Which is why I mentioned
the current/time/efficiency relationship the other day. When you
say "on completely" then you'll have to consider the series
resistance

(btw, the 56R/220p on the row control inputs is just a simple
noise filter and has nothing to do with brightness)

> here I actually was wondering if a 4mhz 16F84 is fast/powerful
> enough to present a good display.....now that my little
> experimenter set up is working

What will ultimately affect the quality of the display is how long
the refresh cycle is, which depends on how many shift registers
you need to get data to and how fast an effect like scrolling is
performed. A fast scroll needs faster updating (hence the tilted
characters seen when the updating is not fast enough). You
could drop in an F84A-20 if you wanted to

> could a darlington transistor array be used in this application?
> I was looking at a ULQ2003A, and was wondering if that could
> be connected somehow...

Those drivers are quite common in displays. However, I have
repaired displays in which the driver chips got too hot (the
individual transistors can handle a reasonable amount of power,
but you have to watch the dissipation for the whole chip) and have
either died or scorched the board and caused dry joints, which
can get nasty. With individual transistors you have the opportunity
for better cooling. Also, the faster the transistor switches, the less
time it will spend between on and off and so run cooler

> I get the idea of how the individual transistors make the circuit,
> but this array isn't obvious to me how to hook it up....

How do you mean ?

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