Backlight failure in 2*20 LCD with 16 pins

• Oct 2, 2003

• #1

Z

ZeleC

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lcd backlight

hello i used to work on a 2*20 lcd with 14pin with no backlight
now i purcahsed a 2*20 lcd with 16pin and the last two pins are used for backlight , but it is not working wth me .
what is the problem ?
as it lokes in the datasheets that for different V we will have differnet backcolor but nothing changing .
i noticed that r two other pins on the side of the screen ,one wth the sign +
so does these two pins have something to do wht the backlight ???
can anybody give me some help here...
thx in advance

 

• Oct 2, 2003

• #2

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tonyfic

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Re: lcd backlight

I don't know if they changed since I last used them but. they used a ring of LED's for the backlight and you had to use an appropriate series, current limiting resistor or it would be ruined...They used to run from a +5v source.

 

• Oct 3, 2003

• #3

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mr_ghz

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Re: lcd backlight

Hi ZeleC

The 16-pin connector is more or less standardized for such LCD's. Mostly the backlight (LED-Backlight with or without resistor) uses 5V and about 50mA. If these 2 pins are not connected (as in your case) there are two other pins on the board marked with '+' and '-'. These pins are for backlight. Connect them (for security reasons over a resistor) to a 5V supply.

Bye

 

• Oct 5, 2003

• #4

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Aoxomox

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Re: lcd backlight

As far as I remember my module needs 4.3V for the LED. So you NEED!! a resistor to limit the current drawn from 5V.

50mA is OK. so calculation should not be to difficult.

AoXoMoX

 

• Oct 6, 2003

• #5

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Sebi

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Re: lcd backlight

Most of cases You can find on PCB two zero ohm (jumper) appeared as 1206 SMD resistor or only pads. Follow the layout and determine the right position of jumpers. I've measured the backlight current, and it suck 300mA(!) at 4.3V.

 

• Oct 6, 2003

• #6

Fragrance

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Re: lcd backlight

hi

sebi is right some time a zero ohm resistor added for the safety of back light may be this is faulty try to checked the back light applying direct voltage to the treminal where back light is installed to vaify it if its glow
then the zero ohm series resistor is faulty. or back light is faulty

 

• Oct 9, 2003

• #7

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ZeleC

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well guys i did tried to aplly a voltage to the on the backlight leds but it didnt worked and i tried to connect a voltage to the other two pins but same thing ... nothing
well i noticed that some smd resistors on the pcb are not found .....???
im using a 162e lcd if anybody heard of..
thx guys for ur help

 

• Oct 9, 2003

• #8

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mr_ghz

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Re: lcd backlight

Hi ZeleC

Can you give more information about your display? Is written more than 162e on the board? Do you have a manufacturer? Or you can also upload a photograph of the board.

Bye

 

• Oct 22, 2003

• #9

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ZeleC

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well its from displaytech ...

 

• Oct 23, 2003

• #10

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mr_ghz

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Re: lcd backlight

Hi ZeleC

I tried to download the datasheet from **broken link removed** but the sheet is not available...
Do you have it??

Bye

 

• Oct 23, 2003

• #11

M!k

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Re: lcd backlight

This is the correct link to the PDF (seems that they forgot to update their page):
**broken link removed**

Concerning the different colours:
depending on the order code (-3LP / -4LP/...) this LCD is available with different backlight colours (see page 3). Correspongly different currents are drawn @ different voltages. But you can't adjust the colour by varying the voltage!
It also seems that it's available without backlight or with EL backlight. Compare the size: is it 80x36x11 (It's not 100% clear: without backlight or EL ?) or 80x36x14 (with LED backlight; see page 2). If it's with EL backlight you've to apply 100Vac @ ~400Hz (see page 3).


Mik

 

• Oct 23, 2003

• #12

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preethi_das

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Re: lcd backlight

directly u cannot connect the back light use a calculated resistor for specified current in the data sheet

 

• Dec 8, 2003

• #13

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phongwiroon

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lcd backlight is a normal led , u can use the circuit that u light up the LED. anyway the neon lamp can use for a lcd backkight

 

• Jan 23, 2004

• #14

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fuzcub

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Re: lcd backlight

I've got an LCD display in which the backlight is a single series string of LED's , meaning that the backlight requires 14.5 volts at 25 ma ( 7 x 2 volt leds).
At 12volts the backlight *just* lights up, at 14 volts it's about right, so I use a 16 volt supply with a current limiting resistor.
So all up the LCD requires +5v,-7v and +16v, but it's big, bright and very easy to read at a distance.

Cheers, fuzcub