Max 7219

Archiver

Hi,
Does anyone know how to control two cascaded max 7219
connected according to the original datasheet
Data => Din1 => Dout1 => Din2
Clk Parralell
Load parralell

they talk about sending a NO-OP command
but I can't get it to work
I get just the same info on both devices.



Ren

Archiver

Hi!

I have a few questions:

I don´t fully understand the concept of sourcing and sinking current. I
want to use a MAX 7219 led display driver to control 64 12V lamps. The
MAX 7219 IC has has eight legs for segments and eight legs for digits.
Now as I understand it, if I want to turn on a led segment, I need the
7219 to turn on the correct segment leg and its coresponding digit leg.
The segment leg sources current and the digit leg sinks current. But
what excactly does that mean? Is it correct to say that the segment leg
provides the current needed for the led to light up and that the digit
leg which sinks current, is just a switch latching the current towards
ground?

If that is true then my next question is; how can I step up the voltage
and current to supply my 12V/21W incadecent lamps? I have previously
used a recipy from Matt Gillilands Microcontrollers Cookbook in which
the Basic Stamp uses a 7406 IC coupled to an IRF511 to drive a 12 volt
lamp. And that works for me when I have a +5v from the Stamp to set
things in motion and I can probably use that setup to boost up the
voltage on the segment leg of the IC. But what happens on the other
side, the digit end of the 7219, where there is no high signal to
switch on the 7406 and IRF511? Or is it? What hardware setup can I use
on the digit side to sink more current?

And another question: Is it true to say that an N-channel MOSFET is
turned "on" when it receives a high signal at its gate, and that a
P-channel MOSFET is turned "on" when it receives a low signal?

Best regards Baard Toerdal

Archiver

"Sourcing" and "Sinking" current.

You first need to know that the PIC pin can
'source' current (provide a low-impedance
connection to a +5 volt line) OR 'Sink' current
(provide a low-impedance connection to Ground).

It does this with two transistors inside the chip.
When you want a 'high', the transistor to ground
is turned OFF, and the transistor to +5 is turned
'ON'. This is also called a 'push-pull' interface,
because it can 'push' a line to +5 volts, or 'pull'
a line to ground.

You can configure the PIC pin as an 'open-collector'
output, in which the PIC can 'sink' current to ground,
or let the pin 'float' high (with an external pull-up
transistor (1K Ohm or so)).

Now, the 7219 is a very useful chip for driving
LED displays. To do this it 'scans' the rows and
columns of its pins. For each row, it turns on
(sources current from +5) 8-bits of data, then sinks
(connects to ground) the column pin for that
row. I believe it has an internal current
limiter -- because if you directly connect an
LED to +5 and Ground it will burn out. You
need an additional resistor to limit the current.


I believe you can get more current (needed to
drive your 12 volt lamps) if you connect
external transistors (or a driver chip) to the
pins of the 7219. I believe there is an application
note for this -- see the MAXIM-IC website.

--- In basicstamps@yahoogroups.com, Baard Andreas Toerdal
<basic@t...> wrote:
> Hi!
>
> I have a few questions:
>
> I don´t fully understand the concept of sourcing and sinking
current. I
> want to use a MAX 7219 led display driver to control 64 12V lamps.
The
> MAX 7219 IC has has eight legs for segments and eight legs for
digits.
> Now as I understand it, if I want to turn on a led segment, I need
the
> 7219 to turn on the correct segment leg and its coresponding digit
leg.
> The segment leg sources current and the digit leg sinks current.
But
> what excactly does that mean? Is it correct to say that the segment
leg
> provides the current needed for the led to light up and that the
digit
> leg which sinks current, is just a switch latching the current
towards
> ground?
>
> If that is true then my next question is; how can I step up the
voltage
> and current to supply my 12V/21W incadecent lamps? I have
previously
> used a recipy from Matt Gillilands Microcontrollers Cookbook in
which
> the Basic Stamp uses a 7406 IC coupled to an IRF511 to drive a 12
volt
> lamp. And that works for me when I have a +5v from the Stamp to set
> things in motion and I can probably use that setup to boost up the
> voltage on the segment leg of the IC. But what happens on the other
> side, the digit end of the 7219, where there is no high signal to
> switch on the 7406 and IRF511? Or is it? What hardware setup can I
use
> on the digit side to sink more current?
>
> And another question: Is it true to say that an N-channel MOSFET is
> turned "on" when it receives a high signal at its gate, and that a
> P-channel MOSFET is turned "on" when it receives a low signal?
>
> Best regards Baard Toerdal

Archiver

--- In basicstamps@yahoogroups.com, Baard Andreas Toerdal
<basic@t...> wrote:
> Hi!
>
> I have a few questions:
>
> I don´t fully understand the concept of sourcing and sinking
current.


The simple way is to think of a battery and a light.

if you run a cable from the positive to the light, you are sourceing.

if connect the light to the battery and run a wire to ground you are
sinking.

Sinking devices, NPN's are more common and less expensive. bottom
line, for lights NPN's are usually the first choice.





<snip a paragraph>


> If that is true then my next question is; how can I step up the
voltage
> and current to supply my 12V/21W incadecent lamps?

Incandescent often means filiment lamps. that often means an
internal coil and if/when the coil breaks, you can get a surge of
power onto your chips.

Here the gamble is that if it breaks at the point furthest from the
MOSFET, the coil is still in the loop. if it breaks at a point
closes to the MOSFET, the coil is out of the loop. 50/50 chance.

If you use MOSFET's, use high amp ones as they will not be much more
in cost.


<snip>

Dave