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Topic: Why connect A and K on LCD display (Read 797 times) previous topic - next topic


I have found several different pin-outs for LCD displays such as the one attached, which matches my display pin set (16 pins x 1 row).  ESUMIC LCD Module Display for Arduino (Blue2004) link

In some, the K and A are connected, and in some they are not.  K is GND (LED-) for back-light, and A is Vcc (LED+)  for back-light. 

One other observed difference is some have a 220 ohms between Vcc and A (LED+).

Is there any documentation on the correct connection showing why (why not) connect these and why (why not) add resistance to +5V?



The LCD itself has a 14-pin interface with a more or less standard interface originally introduced by Hitachi.

A lot of the early LCD modules had no backlight but most of those that did required a high voltage (more than 100v as I recall) to operate that backlight.  The connections were at the end of the display.  

Most modern LCD modules do incorporate an LED backlight and two pins are now typically added to the pc board design to provide an interface to that backlight.  If a particular display does not have a backlight the same pc board can be used but those pins will be unused.

The pc board typically has provisions for a current limiting resistor but the display manufacturer may install a zero ohm resistor in which case the final circuit will require an external current limiting resistor.

So - there is no 'universal' documentation that will give you the answers to your questions.  You need to use the documentation that matches your particular hardware.  In the absence of such documentation you can usually follow the traces on your pc board to determine the answers.


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