wondering what this extra connector is for on this LCD display (HDM128GS24 w/ T6963 controller)

[Dan1256]

https://www.mpja.com/LCD-Display-240-X-128-Graphic-with-Backlight/productinfo/31003+OP/

I just purchased this LCD display and was wondering what the extra red/black wire is for. You can download the datasheet from the above link. I'm also wondering what the data sheet means by "# Has built-in inverter for negative power supply" on page 23.

 

[ronsimpson]

I think it is for the back light.
LED 900mA 4.5V

 

[AnalogKid]

Liquid Crystal Displays require a negative voltage (at very low current) to operate, but the world likes things with single, positive voltage requirements. To handle this, some displays have a charge pump built into the device to generate the negative voltage. The Amazon description says the display needs -12 V, which contradicts the manual.

ak

 

[ronsimpson]

From what I got from the manual is that there are several different options for back light.

The Amazon description says the display needs -12 V, which contradicts the manual.

Pin 3 is -12.5V

The two wires are labeled K, A for the LED.
Note you need to add resistors.

 

[Dan1256]

From what I got from the manual is that there are several different options for back light.

Pin 3 is -12.5V

The two wires are labeled K, A for the LED.
Note you need to add resistors.

That's what I was thinking, but there's 2 traces on the board labeled 'A' and 'K' and they don't have any connection to the black/red wires.

 

[Ian Rogers]

I don't use that particular screen but!! The negative voltage generator is optional... Yours has one!

There will be a Vee output usually after the databus on pin 17 ... This will give about -17v.. place a pot between this voltage and the 5v rail, feed the center tap to VL... Adjust brightness.

The external backlight is a new one on me... Usually they are connected to A and K but you would need to wire them yourself... I suspect that the LED's take a bit of power ( hence the size of the wiring ) I should imagine the traces on the board won't carry the load... Going off the datasheet the LED's are looking for up to 2.25A... WOW!! I would run them a lot lower than that!!!

 

[Dan1256]

Thanks Ian. I'll try that.

 

[Dan1256]

OK I did that and I think I just fried my board. The led on the 3v3 <-> 5v power supply won't go on. Is there any way to tell if its fried. It seemed to be working as far as my code running on the board and getting a status code back but there was no image on the screen whatsoever. The code I'm using is at **broken link removed**
[Edit: no I think I'm OK - I may have shorted something out temporarily]

 

[ronsimpson]

Can you shine a flash light on the display? Front? Back?
Is there a "contrast" pot?

 

[Dan1256]

I just tried the flashlight to no avail and there is no pot on the board anywhere. I'm looking at some diagrams for other LCD's and I'm wondering if the pot is supposed to go from gnd to Vee with the center tap on Vl.

 

[Dan1256]

I tried connecting one side of the pot to ground and then to Vcc and after adjusting it both times at some point I get a bunch of lines across the screen. Must be doing something wrong in my code. I'll have to read the data sheets over real good.