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Dim Backlight for Graphical LCD to 16F877

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tiwari.sachin

New Member
Hello

I have interfaced a graphical LCD to PIC16F877. This graphical LCD operates on 3.3 V. Because of this i have a voltage divider on all the I/O pins that go to the LCD through PIC. I have attached the connection details.

My doubts are

firstly, Is it the right way to connect. I know we can use level converters but i dont really have them with me now

Second, the LCD is working fine but the LCD back light is very dim. ie to LED+ i am connecting 3V through a voltage divider. before connecting to LED+, the voltage reading is 3V but once i connect to LED+, the voltage drops to 2.6 V and because of this the backlight is very dim. This, i am sure is due to internal resistance. How can i rectify this problem? The display part seems to work fine. The problem is with the backlight.

Regards
SACHIN
 

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ericgibbs

Well-Known Member
Most Helpful Member
Hello

I have interfaced a graphical LCD to PIC16F877. This graphical LCD operates on 3.3 V. Because of this i have a voltage divider on all the I/O pins that go to the LCD through PIC. I have attached the connection details.

My doubts are

firstly, Is it the right way to connect. I know we can use level converters but i dont really have them with me now

Second, the LCD is working fine but the LCD back light is very dim. ie to LED+ i am connecting 3V through a voltage divider. before connecting to LED+, the voltage reading is 3V but once i connect to LED+, the voltage drops to 2.6 V and because of this the backlight is very dim. This, i am sure is due to internal resistance. How can i rectify this problem? The display part seems to work fine. The problem is with the backlight.

Regards
SACHIN

hi,
What value is the resistor that you have in series with backlight LEDs.???
 

tiwari.sachin

New Member
Dim Backlight for LCD

100 Ohms is what i am using for LED

As of now i am thinking of changing the power supply.

Instead of the voltage divider for Powering LCD, i will use zener ckt.


How about just having a current limiting resistor of about 100ohm from zener and connecting it to the LED+
 

Pommie

Well-Known Member
Most Helpful Member
You just need a current limiting resistor from 5V to the LED. It should drop 2V at the required current, this assumes the LED has a series resistor so it works on 3V. So, for a current of 20mA the resistor should be 2/0.02 = 100Ω. If the LED current should be 50mA then the resistor should be 40Ω.

If you don't know the required current then remove the resistor from LED to Gnd and reduce the top resistor until it is bright enough. Do you have a link to the data sheet?

Mike.
 
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