Help with connection of JM402A LCD's background light?

[mikkokh]

Hi.

Is there any possibly to connect backlight power of this LCD module (JM402A) using that blue connector on left side of it? All 16pins are connected, but Led backlighting does not get any power with pins 15 and 16. Led backlight is undamaged - I' sure about it, because connecting power to "points" K and A in right side of module gets background light on.

In Specifications PDF is written that pins 15 and 16 should deliver power needed for backlighting, but I think that "unconnected" J1-J3 and unplaced resistors R2-R3 can be cause this it problem. So, should this display backlight even to get working with those pins (15 and 16) or is using of those "points" (K and A) only way to get backlight working? If I should use those "points" K and A, should I use those smaller or larger holes near of those marks to connect power to backlight right way? I think that larger holes are right choises, but I want to be sure of it...

Thanks!

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Specifications PDF on URL: http://mikkokh.wippiespace.com/public/d ... 045d01.pdf



Larger Image on URL: http://mikkokh.wippiespace.com/public/i ... e/img1.jpg



Larger Image on URL: http://mikkokh.wippiespace.com/public/i ... e/img2.jpg

[caesar]

Planting the corresponding resistor and enabling one of the jumpers should allow you to use pins 15-16 for backlight.
If you can't follow the PCB traces to be 100% sure then just wire to A and K but remember to use a resistor!

[mikkokh]

Planting the corresponding resistor and enabling one of the jumpers should allow you to use pins 15-16 for backlight.
If you can't follow the PCB traces to be 100% sure then just wire to A and K but remember to use a resistor!

Thank's about answer, caesar!

I think that I should connect "jumper" J1 and put correct resistor to place R2 to enable ground, and then I should connect "jumper" J2 to enable input if background light current. Still... I don't even know why there is need of this resistor R2, because I use external resistor to control current of background Led... Because of this, I think that I can connect pins of R2 together without any resistor. What you think about this??

By the way - There is already resistor R1 connected to serial by that empty place of R2, but I don't know sure why it is there... And one of those smaller holes on right side of screen (near by mark A) is also connected to Led background light through that resistor. How much power output those PCB resistors can handle? Can those even handle whole power of Led backlight?

Because this PCB is build to two sides, I don't be 100% sure about this all... I mean that I don't know if that power goes also some other place after all these modifications. It would be really stupid, but how be sure about it. I think that I should, test it, test it more and test it even more to be sure about it.

[caesar]

To be 100% sure connect +5V and ground through your already used resistor directly to A and K points. Why risk damaging it?

[mikkokh]

Thanks about answer, caesar.

My reason for this is than I would want to do this job with so few cables than I can to do so... I want to prevent broken (with stress) cables before I can even get this screen to work and found/do for it some suitable external case. That's also one of reason why I have soldered that blue ribbon cable connector to LCD module... Ribbon cables are usualy easy to change and them tolerate quite much of external stress.

[caesar]

Well, I'd wire A and K with the resistor directly to pins 15 and 16. Using also some hot glue or tape to make it stick to the PCB.
You could also try with some attention and a multimeter to find the correct PCB paths and it will also look better.

[mattcro]

Most LCDs I've come across have 2 or more resistor places on the PCB, so that the backlight can be wired to the connector either way round, with or without resistors. As caesar suggests, you are probably safest wiring the A and K pads direct to the connector and using an external resistor. You'll need to calculate a value for this resistor based on the specs for the backlight (voltage and current). Usually it's only a few ohms or 10's of ohms for a 5V supply.