LCD displays are fast becoming
the newest must have item for PC heads the
world over. Their ability to reduce the clutter
of a computer desktop and their porno appearance
are winning more and more people over every
day. There are essentially two types of display
to choose from; serial and parallel, referring
to how they connect and communicate with the
PC itself. I wont go fully into the pros and
cons of each here as its not the aim of the
article, what I will say however is that fundamentally
the decision comes down to a cost versus ease
of use issue. Serial displays are easier to
get up and running and are marginally better
supported with software as well as having
some extra features, parallel displays on
the other hand need wiring up yourself but
are much cheaper and for the most part can
still display the same information. Check
out Cheese's
LCD FAQ for some more general LCD info.
In this article I'll be looking
at what is necessary to get a parallel LCD
hooked up and how to actually go about connecting
it. Most parallel displays are very similar
using industry standard interface chips (HD44780
or HD44100) so the pin assignments are often
identical. Here I'll be specifically be looking
at a 4x20 Orient Displays module bought from
Maplins a few months ago which has been used
daily since with no major issues. Similarly
appropriate displays are also available from
Farnell, JPR and RS among other places (often
costing less too). One thing to be aware of
though is that not all LCDs come with a backlight
which would reduce visibility so be sure you
know what your getting when there are many
displays available (in particular Farnell
whose range is unrivalled). Anyway on to the
necessaries then ...
Now you've sorted what you'll
need lets take a look at the baby..... the
thing to note here are the 16 pins at the
top left which we'll be soldering too later.

And the rear ...

A minimum of 16-way wire is
needed to hook the display up however I decided
to use a shielded multicore cable instead
of a ribbon type simply because it looks nicer.
The closest match in terms of independent
cores was 25-way hence the choice in the materials
above. The individual wires are thin ... very
thin, so if you also choose this type you
will need to be careful although the end result
is a lot more aesthetically pleasing in my
opinion ... its purely down to personal choice
of course. The colour coding is also a godsend
when figuring out what goes where!!

A sharp knife is always handy
when stripping back wires especially when
they are quite thin.

Also somewhat essential is a
soldering iron of some type. A fine tip and/or
thin solder would be an advantage as well
given the relatively small size of the wires
and the contacts you'll be soldering too.
Even more important is a steady hand though
:o)

Although parallel LCDs nearly
always have the same connectivity in terms
of pin ordering and their function it is still
worth checking the datasheet for you specific
display to be sure this is the case. Below
is the one that came with the display I got,
if you don't actually get one then pdf versions
are often available on the manufacturers/distributors
website.

Once you know what the contacts
on the display itself are for the next stage
is knowing which pins of the parallel or power
plug to attach them to, handily summarised
below ...
LCD Pin Number
|
Symbol
|
Function
|
Parallel/Power Connection
|
1
|
Vss
|
Display power ground
|
Molex ground (either
black wire)
|
2
|
Vdd
|
Display power +5V
|
Molex +5v (red wire)
|
3
|
Vo
|
Contrast Adjust.
Altered by adjusting the voltage to
this pin, grounding it sets it to maximum
contrast. *
|
Molex ground (either
black wire)
|
4
|
RS
|
Register select
|
Parallel pin 16
|
5
|
R/W
|
Data read/write selector.
Its possible to read information from
a display however there's no need for
it here so grounding it sets it permanently
write.
|
Molex ground (either
black wire)
|
6
|
E
|
Enable strobe
|
Parallel pin 1
|
7
|
DB0
|
Data Bus 0
|
Parallel pin 2
|
8
|
DB1
|
Data Bus 1
|
Parallel pin 3
|
9
|
DB2
|
Data Bus 2
|
Parallel pin 4
|
10
|
DB3
|
Data Bus 3
|
Parallel pin 5
|
11
|
DB4
|
Data Bus 4
|
Parallel pin 6
|
12
|
DB5
|
Data Bus 5
|
Parallel pin 7
|
13
|
DB6
|
Data Bus 6
|
Parallel pin 8
|
14
|
DB7
|
Data Bus 7
|
Parallel pin 9
|
15
|
A
|
LED backlight power
+5v
|
Molex +5v (red wire)
|
16
|
K
|
LED backlight power
ground
|
Molex ground (either
black wire)
|
* You can connect
this to a potentiometer to have a variable
contrast but in both Cheeseman's and my experience
its not necessary.
A word of warning on the above
though, not all displays have a backlight
that runs off 5V, its not uncommon to find
some that require a lower voltage in which
case an appropriate resistor would be needed.
As proof of how generic parallel displays
are you can see that all the other display
sizes on the datasheet have EXACTLY the same
pin functions.

Work in progress ... wiring
it on my knee certainly wasn't ideal ... made
it easier to picture though so be grateful
!!! :o)

The above table can be a bit
on the overwhelming side so I made a circuit
schematic to (hopefully) clear it up a bit.
Both the LCD and the parallel plug themselves
should be numbered making it somewhat easier
(the diagram is looking at the back of the
plug if yours isn't numbered). Its worth pointing
out that the +5V lines can be joined together
as can the grounds so only a single molex
connection is needed.

Here you can see the diagram
again but this time referenced to my actual
display and plug so you can compare theory
and reality (the colourings are the same).

The full sized picture used
above.

A close-up view of the back
of the parallel plug. The contacts are similar
to small "cups", I found it useful
to fill these with solder first then to simply
reheat it with the wire in place ... otherwise
you might find yourself short of hands !!!

A final shot of the back of
the display, given how thin the wires are
it might be a good idea to somehow fix the
main cable to avoid any undue direct pressure
on the display contacts.

All that's left is to tidy up
and hook up the power. A parallel shell (below)
can help make the connection to the PC a bit
more sturdy and attractive. How you connect
the display will largely depend on how you
choose to mount it (externally or internally)
but will likely involve either the parallel
wire being passed out or the power line into
the case. I personally made an external stand
for my display which basically left me with
a couple of options for connecting the power.
Either somehow feeding the bare molex into
the case to be connected inside or to make
an external connection. The former is easier
but I chose the later to make the display
totally detachable and independant, plus it
looks better !!

Here you can see the finished
display mounted with the parallel and power
plugs ready to be connected (I'll cover the
stand in an article soon)

I handled the power by mounting
some sockets in a spare PCI blanking plate.
I connected a male molex to two 2.1mm power
sockets (JK09K @ £0.99), one for +12V
and the other for the LCD's +5V (which I also
put a switch on FH97F @ £1.09). I also
put a connector straight through so I could
power things inside the case from an external
source. All I then had to do was stick a 2.1mm
plug (HH60Q @ £0.49) on the end of the
LCD power cables and it was ready to go. If
you also choose to do this make sure you keep
the polarities consistent eg. centre channel
of the plug/socket as +ve and the outer as
ground.

The mounted plate made things
neater and easier for me in the long run.

The diplay ready to go ...

When you first boot up your
LCD you should have alternating lines of totally
filled characters and empty ones - this is
the test signal and a good sign ... it means
that the wiring part was a success.
... and just to prove that
it does actually work !!!! (good tune too).

I'll be brutally honest - if
you don't know which end of a soldering iron
to hold then I'd forget you ever read this
and head over to Matrix Orbital's website
ASAP. However I would also say that with very
minimal experience and skill you could still
wire up a parallel LCD pretty easily. Once
you get into it its actually quite simple
and nowhere near as daunting as I imagined
when I first read about the possibility of
doing it. While most LCD's aren't cheap there
isn't all that much chance of it not working
as long as you're careful so the potential
saving is well worth giving it a go in my
opinion, just getting the confidence up is
half the battle :o).
Its often commented that parallel
displays aren't as well supported with software
as their serial partners ... I urge those
doubters to look specifically at ...
LCD
Center &
LCD
Smartie
... both of which I've used
and work flawlessly. There is very little
that you cant do with these two as they both
feature full Motherboard Monitor and winamp
integration as well as much much more (such
as game stats or site news updates). Both
will need a port initialisation program to
be installed (available here)
but apart from that they are incredibly simple
to use.
I hope this guide has in someway
helped those of you in two minds or those
confused about carrying this out ... all the
best and good luck.