HELP - Circuits for HD44780 controller based LCDs

Garfield · Post by **Garfield** » August 2nd, 2005, 1:40 pm

Hi!

I bought a LCD with a controller based on HD44780 but i don't know which circuit i must use to interfacing with the parallel port.

I ask for that they indicate me a circuit that functions with a LCD 4x20 HD44780 controller based and where I can control the BackLigth.

Thanks for the help.

Garfield

Post by **IFR** » August 2nd, 2005, 5:12 pm

Hi Garfield

Welcome to LCD Smartie forums! For informations about the circuit go to this page http://lcdsmartie.sourceforge.net/circuits.htm. Another guide that I like is at http://www.moddershq.net/guides.asp?guideid=13

There are two ways to control the backlight. Either you install a potentiometer or you follow the set up that can be found on this page http://www.lansley.co.uk/forum/phpBB2/v ... .php?t=187
(I haven't tested it though)

Garfield · Post by **Garfield** » August 3rd, 2005, 8:58 am

Hi!

Thanks for the tips. I will try the solution related in this link http://www.lansley.co.uk/forum/phpBB2/v ... .php?t=187. I only wait not to burn the LCD.

Another question is about to use an external 5V power supply to feeding the LCD. If I use the external 5V power supply, as it would be the scheme to connect it to the LCD (which bolts that would bind to the LCD)?

Another one: Can I use an USB Port power to feed the LCD?

Garfield.

Post by **IFR** » August 3rd, 2005, 7:20 pm

Im not sure what you are asking but basically, you want to connect the 5v to pins 2 and 15.

Apparently, you may use a usb port to power your lcd (since usb delivers ~5V) but I haven't tested it so try it at your own risk. You should check with a multimeter before proceeding.

_X7JAY7X_ · Post by **_X7JAY7X_** » August 4th, 2005, 4:44 am

For a HD44780 the pins are as follows:

Pin 1 - GND
Pin 2 - +5v
Pin 3 - Contrast (using a 10k pot)
Pin 3 - R/S
Pin 4 - R/W (Read/Write)
Pin 5 - Enable

Pin 6 - 14 -- Data

When using 4 bit interface, only pins 10 - 14 are connected.

To connect a 5v external power supply you would need to connect to pin 1 , 2, and 3.

J

Garfield · Post by **Garfield** » August 5th, 2005, 8:18 am

If the LCD have a BackLight the pins 15 and 16 I must to connect to the 5v external power supply if I use it? Or if I connect the pin 16 (BackLight) to the pin 17 of Parallel Port with a transistor, the pin 15 (BackLight) is connected to 5v external power supply?

Thanks for the help.

(Excuse my bad English)

Garfield

_X7JAY7X_ · Post by **_X7JAY7X_** » August 5th, 2005, 1:40 pm

You will need to connect an external power supply for the backlight, however, you can use USB or power from a connector in your computer. You need to connect a limiting resistor to the backlight, otherwise you will burn it out. I think I am using a 10 ohm with no problems.

J

Post by **IFR** » August 6th, 2005, 3:52 am

Garfield wrote:If the LCD have a BackLight the pins 15 and 16 I must to connect to the 5v external power supply if I use it?

true if you want to leave the backlight always on

Garfield wrote:Or if I connect the pin 16 (BackLight) to the pin 17 of Parallel Port with a transistor, the pin 15 (BackLight) is connected to 5v external power supply?

true if you want to be able to use the backlight feature.