[Soekris] LED controller

[Bernd Walter]

On Sun, Aug 08, 2010 at 05:09:26PM +0800, Pete Kay wrote:
> Hi
> 
> Thank you for your suggestion.  I have got a few 74HC595 ICs and I
> would like to try to use GPIO to drive this IC which will then in
> light up the LED.
> 
> Does anyone know how to use GPIO to generate the CLK signal?  I know
> 74HC595 needs CLK, Latch, and Data-in.   Where can I find any tutorial
> on how to use 3 GPIO pins to drive this IC?   How do I synchronize
> these three signals?   Please forgive my newbie questions as I am just
> beginning to learn about gpio.

This signal is named clock because when used in e.g. a state machine
you connect it to the system clock, but if you see the device alone you
just need a signal change for data takeover and not a periodic clock.
Setup data and latch signals, then toggle clock down and up again and
you are done.

You can also consider using an I2C chip, such as a PCA9555 or MCP23016,
which are happy with 3.3V - the MCP is also available in DIP housing.
NXP also has some I2C 16x 20mA LED driver with and without bright control,
but for signal LEDs you rarely need 20mA.

Another option might be to connect a microcontroller.
There are many with I2C or USB, but unlike the last option they need
programming first which may or may not be within your skills.

> Any help or hint or pointer will be greatly appreciated.
> 
> Thanks,
> P
> 
> On Sat, Aug 7, 2010 at 3:27 PM, Alvar Kusma <alvar at raamat.polva.ee> wrote:
> > Pete Kay kirjutas:
> >
> >> I am trying to have my Soekris board to somehow control a set of 16
> >> LEDs,
> >> What are the components that I can purchase
> >> off-the-shelf for this kind of thing?
> >
> > Net5501 has 12 general purpose IO pins on JP5, which are accessible from
> > userspace. But if you need more than that, then use PIPO register like two
> > 74573-s latches, connected to GPIO pins (if i remember correctly, then
> > PC87366 is 5V tolerant). Software then is a bit more complicated, but not
> > much.
> >
> > Another way is to use SIPO registers. For realization example see
> >
> > http://www.arduino.cc/en/Tutorial/ShiftOut
> >
> > Simplest way of course is to try directly with existing GPIO-s, but this
> > limits LED count to 12.

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.