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[Moved] 20x4 lcd on and off problem

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Ofcource my concept is to save power. but juat powering off the backlight does not work, because the contents and the characters in LCd are still visible.
 

gauravkothari23 said:
...juat powering off the backlight does not work, because the contents and the characters in LCd are still visible.
Click to expand...
You know that most of lcd modules need only 1mA to work (like CrystalClearTec) and some use only 100nA or even below?
 

gauravkothari23 said:
Ofcource my concept is to save power. but juat powering off the backlight does not work, because the contents and the characters in LCd are still visible.
Click to expand...

To make the display "disappear" you have to simply change the voltage on Pin3 (contrast)
 

@kripacharya.....its not possible to recommend someone to open the gadget and simply turn the pot to 0 to put ur lcd in off state. so am in search of simple circuit which can help me in doing so by pressing a single key.
 

gauravkothari23 said:
@kripacharya.....its not possible to recommend someone to open the gadget and simply turn the pot to 0...
Click to expand...
The pot is external. You do not open anything. You may not have one (potensiometer/trimmer) but it is recommended in lcd documentation so you can change the contrast value.

ps. I do not recommend to just turn down the contrast, because the HD processor will still need the power to work. It's unimportant to turn characters off without turning off the HD chips
 

Hi,

FDV304P, FDN360P, SI2333CDS read datasheet.

Klaus
 

The CPU datasheet indicates 20mA at 5V @ 12MHz about the same as a 20mA LED
This transmissive LCD is a charge storage crystal device that blocks light with proper bias and takes very little current. The LCD has very little dynamic power compared to the CPU.

So as in laptops. the LCD display consumes very little power while the backlight and CPU consume the most. ( unless driving high speed 3D rendering on GPU )
 

Hi all....
thanks all for your help.
As i stated before that my lcd is not properly working on port 3^5 and port 3^6.... but when i connect the same to port 2^5 and port 2^6 is working absolutely fine. even there is not backlight as well as text displayed on the screen and also the voltage shown on port 2 was 0v. can u please tell me why it does not work on port 3 then if it can work on port 2

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Now it works absolutely perfect on port 2..... but now the problem is when i press the key to on the lcd..... the lcd gets on and also characters are visible in it but after 5 seconds the backlight automatically goes off and the characters are been visible..... dont know whats wrong now....
 

20x4 lcd gets dim when on

Hi all...
I have made a small project using 89S52, 20x4 LCD and keypad. my concept is to keep the lcd off at initial stage and when ON button is pressed from keypad..... the lcd should get ON.
I have used a transistor as a switch to on and off the lcd.
Lcd is connected to port 1 and supplied direct power to lcd(pin 2 and 15).
Ground pin(pin 1 and 16) is connected to collector and being forwarded using emitter of bc547 and pin P3^5 of 89S52 is connected to base of Bc547.
code is somewhat like
at initial stage port 3=0xff
when key is pressed
port 3=0x00...
it works absolutely perfect..... but the problem is when the lcd gets on..... its very dim.....
can anybody plz help me.....
 
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Re: 20x4 lcd gets dim when on

LCD's require 5V to display an image, if the supply is only 4.5V the display will be off or very faint. If you are switching the 5V with a transistor it may be dropping say .2V or .3V this would account for the dim display, measure the supply voltage with a volt meter to the display. A solution maybe to turn up the 5V by a small amount.
 

Re: 20x4 lcd gets dim when on

But it is recomanded to use MOSFET to switch the supply for the display as it switches faster and has low on resistance, making the voltage drop very small than using BJT transistor.

Or there is a function to turn off the display with command. you may use that function. Then no transistor is needed. But with this method, power consumption will be little bit higher than using an external transtor/MOSFET.
 

Re: 20x4 lcd gets dim when on

Alternatively, the LCD module may have a CONTRAST pin. This actually varies the drive bias to the segments and has the effect of also changing the viewing angle. The connection usually takes the form of a pot between the supply and ground - the datasheet for the display will usually give a suitable specimen circuit with values.
 

Re: 20x4 lcd gets dim when on

I'm assuming that your 20x4 LCD is a module complete with driver electronics and just a 4 or 8 bit data interface, rather than the pure LCD glass unit with all segments and backplane brought out? If you are trying to drive a pure glass unit, be aware that LCDs must be fed with an AC (biphase) drive - they must not be driven with DC alone or they become polarised. (Your question said that it GETS dim when on... Just a thought!)
 

Re: 20x4 lcd gets dim when on

yes... the lcd gets dim when i try to turn it on....
i am using 20x4 normal character LCD.
Mosfets basically works on high voltage so how can i use it to turn on and off the lcd at very low voltage.

- - - Updated - - -

the lcd is working on 4.2 to 5v...
but after using bc547....the lcd is getting only 2 2 v....
what should i do....

- - - Updated - - -

What MOSFETs can help me....
i mean the part no.
 

Re: 20x4 lcd gets dim when on

the lcd is working on 4.2 to 5v...
but after using bc547....the lcd is getting only 2 2 v....
what should i do....

- - - Updated - - -

What MOSFETs can help me....
i mean the part no.
Click to expand...

I notice that you are asking the same questions as in your previous "LCD on/off" threads, so this thread has been incorrectly started as a new one.

Despite of the various suggestions that have been made in the previous threads, you apparently haven't yet recognized the nature of the problem and corrected your circuit respectively. Due to lack of a complete problem description (schematic, measurement of all relevant circuit voltages) contributors to this thread are still guessing what's exactly going on.

To me it looks like you either have a unsuitable configuration of your power switch transistor, or are controlling the transistor with unsufficient base current. The latter can easily happen if you don't understand the specific properties of 8051 IO ports.
 

Re: 20x4 lcd gets dim when on

Hi,

I agree with FvM.

What MOSFETs can help me....
i mean the part no.
Click to expand...
Especially this I answered in the other thread. With part numbers and connection information.

It´s demotivating if we try to help and you don´t use it

Klaus
 

Re: 20x4 lcd gets dim when on

Yes u r right.
i have started this new thread with the same topic.... because in previous thread the concept was still not clear to me.... as i am new to Electronics and programming..... its bit difficult for me to recognized and understand the working of components....

- - - Updated - - -

sorry Klaus.....
My intention was not to demotivate you.... i have searched for the MOSFET in the market which you recommend me.... but thw datasheet i gone theough..... it did not made me understand anything.... so i started a new thread
 

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