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LCD Backlight Control : Some questions

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Urahara

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Hi

Am trying to control the backlight of a 20x2 LCD character module with a PIC pin. The main purpose behind it is to conserve battery power, with the PIC switching the backlight off before going to sleep after a period of inactivity.

Have googled and found something like this as attached. My questions :

1) Is this how this works :
- During normal activity, I will output a "1" to pin C2 to turn on the LCD backlight.
- I don't have to output a "0" to pin C2 to turn off the backlight since the PIC will effectively not output anything to the pin (hence a "0") when it goes to sleep. When it wakes up, it goes back to the earlier state (ie a "1") and turns on the backlight. Is this correct?

2) Researching on the net led me to believe a MOSFET would be a better choice? Why? And what would be the (cheaper?) equivalent of the 2N2222 if so?

Your comments appreciated. Thks!
 

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  • LCD Backlight.jpg
    LCD Backlight.jpg
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Hi

Am trying to control the backlight of a 20x2 LCD character module with a PIC pin. The main purpose behind it is to conserve battery power, with the PIC switching the backlight off before going to sleep after a period of inactivity.

Have googled and found something like this as attached. My questions :

1) Is this how this works :
- During normal activity, I will output a "1" to pin C2 to turn on the LCD backlight.
- I don't have to output a "0" to pin C2 to turn off the backlight since the PIC will effectively not output anything to the pin (hence a "0") when it goes to sleep. When it wakes up, it goes back to the earlier state (ie a "1") and turns on the backlight. Is this correct?

2) Researching on the net led me to believe a MOSFET would be a better choice? Why? And what would be the (cheaper?) equivalent of the 2N2222 if so?

Your comments appreciated. Thks!
You cold well use 2n2222 and i fear N Chl MOSFETs like 2N7000 or BS170 would be costly. You may see Digikey prices. The scheme appears correct
that you have to output a '1' for backlit to be ON
 
thks Sarma! Will check them out.

A near Idea from EDN Nov2000 is appended here. It would of course control the entire supply to the controller. It might help guide your design.
 

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  • Ideas Nov2000.pdf
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