LCD anode / cathode connections - Electronic Circuits Projects Diagrams Free

pc88 · 14th June 2007, 06:36 PM

Hi,

I have a lot of unknown LCD displays (intelligent, HD44780 based), and many of
them have anode (A) and cathode (K) connections. I was wondering generally
how to use them. Are they for a backlight? Do I need to supply a negative
voltage, and if so, what kind of negative power supply do I need?

I've attached a pic of the A and K connections for one of the lcds I have.
The A pad is close to a + supply pad and the K pad is close to a GND pad,
and it seems they are positioned for easy mounting of smd parts.

Thanks,
pc88

ericgibbs · 14th June 2007, 06:59 PM

hi pc,

Usually on the LCD, is a backmounted LED [Gn] that runs the full length of the display and it fits between the LCD and pcb.

From the pix you have posted, that one has no LED, just the pcb track, if it had one already fitted
two of the round holes would have been used.

The SMT pads are for series current limit resistors for the LED diode light when fitted.

Gayan Soyza · 15th June 2007, 11:55 AM

Hi pc88!

Some most character LCD panels the last two pins in the data line array (in your ribbon cable) goes to the LED back light. But it seems like bigger one than other character LCD’s or a different type.

Go following the two tracks A & K & see where it meets.

But LED back light is not the main feature. It’s an additional feature you can replace a backlight with normal 3mm LED’s with a separate 3V supply. Most important is the data lines, contrast adjustment & Vss, Vcc etc….

Most LCD panels can operate in 5V. Give supply through 7805 regulator.

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14th June 2007, 06:59 PM	(permalink)
ericgibbs	hi pc, Usually on the LCD, is a backmounted LED [Gn] that runs the full length of the display and it fits between the LCD and pcb. From the pix you have posted, that one has no LED, just the pcb track, if it had one already fitted two of the round holes would have been used. The SMT pads are for series current limit resistors for the LED diode light when fitted. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

15th June 2007, 11:55 AM	(permalink)
Gayan Soyza	Hi pc88! Some most character LCD panels the last two pins in the data line array (in your ribbon cable) goes to the LED back light. But it seems like bigger one than other character LCD’s or a different type. Go following the two tracks A & K & see where it meets. But LED back light is not the main feature. It’s an additional feature you can replace a backlight with normal 3mm LED’s with a separate 3V supply. Most important is the data lines, contrast adjustment & Vss, Vcc etc…. Most LCD panels can operate in 5V. Give supply through 7805 regulator. __________________ Gayan My Website http://gsmicro.blogspot.com/