Introduction
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Lesson in LCD Basics... What is a GPO? This three letter acronym (yes another one!) stands for
General Purpose Output. These are basically outputs
which can be switched from 5v (max 20mA) to off, via the software controlling
the LCD, and some models even have 'high power GPO's', which can handle 12v and
750mA. What if I want to get more power out
of my GPO's Your in luck! Cheese @
Bit-Tech has come up
with a neat 'piggy-back' device that will allow each of your GPO's to
support 32W @ 12V. Click
here to check it out. Why did you go for a PCB based
approach? Simple. To keep the wiring
minimal and to create a tidy package, which could be applied to many LCD modules
(even VFD's!) and module locations.
The entire design of the keypad is based on the
LK204-25-WB-V manual, and may be applied to other models with slight
alterations, such as the LK204-25PC I.E. if you have a model that supplies 12v
(and a current over 30/50mA) you will need to connect a current limiting
resistor in line with the Led's
Introduction I recently purchased a Lian Li PC71-USB case and decided that I wanted to install an LCD module. After some researching I came across the LK204-25-WB-V by Matrix Orbital and based upon it's online manual I set about creating a custom keypad that will allow me to control a) Winamp, b) the LCD it's self, C) other miscellaneous functions and D) LEDs to notify me about temperature warnings detected by MotherBoard Monitor. The LCD Module - MatrixOrbital LK204-25-WB-V
For this task I decided to employ LCDC to control the LCD. LCDC supports most of the LCD modules by MatrixOrbital, and has keypad and GPO support and many more features such as complete plug-in support. When starting off, I wanted the wiring of the keypad to be minimal, and the components replaceable. The final location of the LCD wasn't a main factor as well, and this left me with one logical option...as I wanted to avoid this:
My initial *want* of a keypad started when I saw this little baby by CoolHand, but I wanted to take it one step further... The Printed Circuit Board and the Keypad Connector
The above PCB was designed in Cadsoft's EAGLE PCB design software, and sent off to CustomPCB.com based in Malaysia for manufacturing. The completed PCB:
This PCB cost £25 as I requested soldermasking, which cost an additional USD10.00! I decided to use header connectors in the design, as these plugs are easy to handle and can be salvaged off old PC's. Of course if you got an UV box and know how to etch your own PCB, you could make this easily, but the size of the tracks and track to track distance may cause some problems if you use my 'design' directly... ...Understanding the PCB The simplest way to understand how this circuit works is like this:
Look at the 10 pins above next to the serial port on the right. Pin1 on the left corresponds to R1 and the right most pin is C5. This is how they are divided:
You should be able to see that the 10pins can support a 25key keypad (5x5). A 'contact' between one of the pins on the left and one on the right will result in the closing of a 'switch'. Looking back at the PCB diagram, JPROW will connect to R1-R4 an JPCOL will connect to C2-C5. This leaves R5 and C1 unconnected for our purposes. This is why I decided to have the PCB interface the LCD to the keypad, because this will require the least amount of soldering of the switch terminals. |
