Using the address- and dataregister approach you can have 8*8= output lines
without address decoder. (So not 2^8=256 like I wrote in a previous
posting.) But with an address decoder you can have 2^8*8=2048 output lines.

To outline the electronic part of the project I'll start with the component
choice. The old 74LSxx serie will do but the 74HCTxx is slightly newer but
consumes much less energy.

Connecting a lot of components to the parallel port you'd better first
buffer its output lines. A couple of HCT245 bus transceivers will do. One
HCT245 and a HCT14 will be some cents cheaper.

The address register may be a HCT374 like I mentioned before. Use pin 17
(Select printer, this is the EPP Address Strobe) of the LPT interface to
clock this register.

You initially required four dataregisters. Adding 3*6=18 seven segment
displays will add another eighteen. Add two for various purposes and you
will end up with twentyfour dataregisters. Clock this registers with pin 14
(Auto Linefeed/Data Strobe) of the LPT interface anded with the the
appropriate address selection line.

An addressdecoder is easily build with four HCT138. You can use two bits of
the address register to select one of the HCT138s and three bits to select a
line of the selected 138. This way you can create the twentyfour address
selection lines, one for every dataregister. Keep in mind that the outputs
of the HCT138 are active low.

It is possible of course to put all this logic on one board and hope you get
it to work. A far better approach is building units that can be build and
tested separately.

pieter

"Ryan Kremser" schreef in bericht
s.com...
is there an easy way to add maybe 136 more address easily, previously i
was
looking into using a led counter to accept a pulse to incriment the value
but now that i'm looking it seems to be a bit more expensive than i was
hoping. I need to be able to drive 6 - 3 digit (7 segment) displays.
plus
an extra 10 could make another aspect a bit easier. Would it actully be a
good idea to use these outputs to control the led's or even with the
difference in price would the counters be a better solution?

"petrus bitbyter" wrote in message
. ..
Ryan,

A very thorough treatment of the parallel port interface you will find :
http://www.beyondlogic.org/

If you read the EPP part you will find out that for output only, you can
use
the method of address- and data register also with a standard parallel
printer port. So with five (LS)374 (*not 473*) you can have 32 outputs.
Some
Googling and you'll find the datasheet.

For low voltages (15V) and low currents (0.5A) a solid state relay
will
be
overkill. A small (reed) relay will do. Farnell sells HE221A0590 from
Breed/Hamlin priced about 3 euro. FAIK it's one of the cheapest. This
relay
will need only a 15mA at 5V so with all outputs on, you still require
only
about 0.5A. You'd better not use this relay to switch the mains unless
you
want to start fireworks.

The outputs of the 374 cannot source the 15mA required so you have to
use
a
transistor or an open collector/drain buffer p.e. a HC07. Keep in mind
that
a transistor will invert the logic. Always place a diode parallel to the
relay coil.

pieter

"Ryan Kremser" schreef in bericht
s.com...
actually solid state would probably be a better solution for me, for
the
most part all i'll be switching is 5 or 12 volt lines. If you could
point me to some more information with the printer port it would help
me
out a lot, so far this seems to be the best option. I was actually
planning on running this through dos, complied used c++ as there will
be
no monitor on the system and it will require fast boot and response
times. Any better alternatives to dos or will i still be able to
access
the parallel port in the same way. again thanks in advance

petrus bitbyter wrote:
Ryan,

You can use an EPP (printer) port. This way you can use a separate
address-
and databyte. Using a 374 type of address register you can enable or
disable
up to eight 473 type data registers without address decoding. That
gives
you
256 output pins which sure will be enough.

Do you really need relays to switch your equipment? They tend to be
pretty
expensive and need a good amount of current. So for twentynine
relays
you
may end up to need some 3A of current. If you want to switch the
mains,
solid state relais are a better choice. (Although they are not cheap
either.) You can also use triacs and optocouplers but you will need
some
extra parts so you're building your own solid state relais this way.

Except from the hardware you'll also need some software. Newer (NT
based)
Windows versions will not allow you to write directly to the output
ports.
One of the methods to circumvent these problem is using a special
driver.
For instance:
http://www.paraport.net/

pieter



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