The Graphic LCD interfacing with AVR

Those who are reading this post might have already worked on character LCD. Well this is Graphic LCD. In this one can control every pixel on the screen. These come in various sizes like 128x64,320x240, 800x640 etc. if you have not worked on a character LCD before you are going to find this very easy and those who have worked on character LCD they are going to find this very very easy.

In short interface of graphic LCD is a simple process.

Here is what I had in beginning.

1)      A development board for avr microcontroller suitable for 40 pin controllers like atmega16, atmega32 etc.

2)      128x64 glcd module jhd12864e.

3)      Various size connectors.(8 pin, 3pin and 2 pin)

4)      And of course 3-dot connected general purpose PCB.

Here is the specification a nice detail one for the LCD. Download.

This one is LG’s LG128643-SMLYH6V.

This one has 3 very good thing that other don’t mention.

1)      Detail of LCD Numbering System

2)      Electro optical characterstics

3)      Ideal connection with 8051 family

Image Taken from robokits.co.in

Here is the datasheet for JHD1284E.Download.

There are few things in GLCD’s datasheet that first timers will be curious to understand.

Pin number	Function	Description
15(cs1), 16(cs2)	Chip selection for controller IC1 and 2.	As the size of LCD goes on increasing the number of controller goes on increasing. This one has 2 ks0108 dividing LCD into 2 64x64 parts. If you are thinking you would require a driver file or driver header file to drive this baby then you are thinking right. Most of the lcd comes with company made driver header files for various controllers to which it can be interfaced. Or one can find countless open source projects dealing with various controllers and using glcd so one can take their display file.
19(led +), 20(led-)	These are for the backlight that every lcd has.  By controlling voltage across these pins one can change the brightness of display.	As the size of lcd increases the current capacity of these 2 pins increases. So it is recommended that these pins have their separate line from lcd’s power and ground pin.(as lcd’s power and ground pin works on very low value of current) To vary brightness one can either connect a 10-100k pot with it or can put into DAC for digital brightness control or if you wanto further compress your pcb you can directly connect it to 5v supply.(this should be done where size is key, power management doesn’t matter, need to light constantly and you have power reset on/off options)
17(rst)	Reset pin. Its active low.	It is connected to supply. It can also be fed into controller if your application requires digital control of the lcd. I honestly never uses peripherals reset pin. In every periphery I use I keep reset pin unconnected. It works just fine as I never take application where digital reset/control is required. For manual reset purpose I use NC push button switches connected to power of the LCD. So in short its not necessary to connect reset pin in order for lcd to work. But still I have given schematic below.
3(Vo), 18(Vee)	Vo is lcd contrast arrangement and Vee is negative driving voltage.	One can connect Vo with a pot(the value of pot depends on amount of variation one needs. Usually I use pot of 1k or 10k) or it can also be fed into DAC for digital contrast control. I on the other hand left it unconnected as I wanted to reduce size as much as possible and I didn’t have to care for power management. Vee is driving control negative voltage. On based on my experience I think its used for digital control when lcd is to be made to go to sleep without reseting it. Usually people connect it with pot  along with Vo. I on the other hand follow my universal rule of seduction (size reduction), the pin that is not required and is active high leave it unconnected.

There are many schematic one can use from the internet. As I am too lazy to draw my own schematic here is a block diagram cum schematic for you.

Block Diagram GLCD

Here is the image of my hardware.

AVR Development Board

USB Programmer

Serial PC-MCU Link

My GLCD BOard Connection

Here is the top layout of my board. 

AVR DEvelopment Board TOP Layout

The board is bought from robokits.co.in.  Meaning it’s a local made board that has JTAG PORT connector for debugging. One can use any local made development board but the manufacturer needs to provide proper programmer for its board. Development boards are freely available over the internet or in a local electronics/embedded shop at various price range (this one is the cheapest). To know more about my development board download the pdf or visit robokits.co.in.