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Author Topic: To use LCD backlight or not use?  (Read 2075 times)
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Hi guys,

I am using an Arduino UNO R3, connected to a 20 x 4 LCD display.
The arduino is powered by a 7.5V battery source.
And the battery would only last for around 1 day.
Currently I am using the backlight of the LCD display on.
So I am wondering, if I do not use the backlight, would I be able to extend the battery life significantly? If so, by how much?

Thanks.
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LED backlights typically take between 40mA and 120mA. The Arduino itself takes around 50mA. Suggestions for reducing current consumption:

- Connect a resistor in series with the LCD backlight (or PWM the backlight) to reduce its current consumption. if you turn the backlight off completely, the LCD will probably be hard to read.

- If the LCD doesn't need to be displaying data all the time, turn off the backlight when there is nothing to report and the user hasn't pressed a button for some time.

- Use a reflective LCD instead of a transmissive one so that you don't need a backlight.

- Use a standalone atmega328p chip instead of the Uno, to avoid the current draw of the USB-to-serial converter. Run it at a lower clock frequency to save power.

- Put the processor in sleep mode as much as possible. See Nick Gammon's page http://gammon.com.au/power.
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LED backlights typically take between 40mA and 120mA. The Arduino itself takes around 50mA.

And the LCD controller and display together typically take a lot less than either of these, sometimes only about 2 mA, so the answer to your question "would I be able to extend the battery life significantly" is yes.

All of the above suggestions are good ones.  You don't even need to build up your own standalone device as there are several software compatible devices available without the overhead of the on-board programming hardware.  The Modern Device RBBB and the Adafruit Boarduino are two examples.


Don
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So I am wondering, if I do not use the backlight, would I be able to extend the battery life significantly? If so, by how much?

Yes, and a lot. There may be no need to get smarty farty about controlling the backlight. Most 20x4 LCDs are I2C and it is common to have a jumper on the adapter which removes power from the backlight.  In the one I have it is at the end of the board and is labelled LED . It has nothing to do with the LED that is immediately adjacent.  In normal room light, the display is fine with no back-light at all.


* 20x4.JPG (74.71 KB, 573x449 - viewed 52 times.)
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Most 20x4 LCDs are I2C ....

I guess you mean most of your 20x4 LCDs.

Don
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No. I guess six sentences can be a bit hard for those with limited reading skills to digest but, hidden deep down in there, I did say:
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In the one I have it is at the en
What I did not say is, the bleeding obvious, that the one I have appears to be typical of what is on the market these days, but I guess the picture was evidence of that.
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Let me see if I have figured this out correctly.  Remember that I have limited reading skills, but my IQ is greater than my age so maybe I can get it right.

Here is what we have to work with:

Quote
Yes, and a lot. There may be no need to get smarty farty about controlling the backlight. Most 20x4 LCDs are I2C and it is common to have a jumper on the adapter which removes power from the backlight.  In the one I have it is at the end of the board and is labelled LED . It has nothing to do with the LED that is immediately adjacent.  In normal room light, the display is fine with no back-light at all.

So, you have one LCD module with a serial interface and you have proven that fact by furnishing a picture of it.  I see no other reason to furnish the picture since it does not show the either the jumper or the LED that you mention.

I have carefully sounded out all of the syllables in all the words in your post and I can still not figure out how, from the information in your post, you can justify the statement that "Most 20x4 LCDs are I2C".

Now remember that my intellectual ability is limited but it seems to me that if a lot of people buy parallel LCDs from reputable sources and have little trouble getting them running you won't see many posts about them.  On the other hand if a lot of people buy serial LCDs from sources that do not properly support their products you will see many posts about them.   The fact that you see more posts about serial LCDs than about parallel LCDs does not lead to the conclusion that there are more of them in use.


Don
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Guys, I have measured my LCD current drawn( only at the Vcc pin). And it is ard 1mA.. Is this in the normal range? And when I measured the backlight alone, it is ard 6mA.. Normal?
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I have found it difficult to sensibly measure the current in a display, hence it didn't take much to persuade me to abandon the backlight altogether, but I would be very suss about such a low figure. I understand the standard current for yer typical 3mm round LED is 20mA.  And that's just for one of them, and the 20x4 is so damned bright... So dc42 suggesting 120mA doesn't surprise me.

It could be that your backlight is already pulsed, and leaning a frequency meter against it could be revealing but not necessarily indicative. The 6mA you see may reflect the characteristics of the meter more than the power consumed.  Nonetheless, it is a hell of a lot less than 120mA and any pulsed supply has to be good! On the other hand you already have the problem and 6mA is a hell of a lot more than 1mA.  In the (ahem!) light of that, no backlight looks pretty good and, if it is like mine, you will probably find it OK. They best way to go is probably to suck it and see by flattening the battery. The situation may be quite different if you have one of those white on blue displays. I know nothing about them but I suspect they are a bad idea.   
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Guys, I have measured my LCD current drawn( only at the Vcc pin). And it is ard 1mA.. Is this in the normal range? And when I measured the backlight alone, it is ard 6mA.. Normal?
You really haven't provided us with enough information to give you a definitive answer.  All we can do at this point is make some guesses based upon some assumptions.

Without a datasheet for your specific LCD module it is hard to tell if your values are normal but as far as the LCD current of 1 mA is concerned that seems possible. 

Without knowing how your backlight is powered and what type of meter you are using we really can't evaluate your 6 mA reading except to speculate on why it is so low.  Nick could be on the right track with the observation that the 6 mA reading "may reflect the characteristics of the meter more than the power consumed" (when you substitute the term 'current' for 'power').  This isn't much of a problem when measuring non pulsating DC or pure sinusoidal AC but can be a big problem when measuring anything else.

Also - many of the forum members do not have English as their native language and may therefore have problems with texting type abbreviations.  I was able to figure out that you meant 'around' when you used the term 'ard' but others may not have done so. 

On the other hand I still haven't figured out what these sentences mean:

    "Nonetheless, it is a hell of a lot less than 120mA and any pulsed supply has to be good!"
    "They best way to go is probably to suck it and see by flattening the battery."


Don

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Guys, I have measured my LCD current drawn( only at the Vcc pin). And it is ard 1mA.. Is this in the normal range? And when I measured the backlight alone, it is ard 6mA.. Normal?
You really haven't provided us with enough information to give you a definitive answer.  All we can do at this point is make some guesses based upon some assumptions.

Without a datasheet for your specific LCD module it is hard to tell if your values are normal but as far as the LCD current of 1 mA is concerned that seems possible. 

Without knowing how your backlight is powered and what type of meter you are using we really can't evaluate your 6 mA reading except to speculate on why it is so low.  Nick could be on the right track with the observation that the 6 mA reading "may reflect the characteristics of the meter more than the power consumed" (when you substitute the term 'current' for 'power').  This isn't much of a problem when measuring non pulsating DC or pure sinusoidal AC but can be a big problem when measuring anything else.

Also - many of the forum members do not have English as their native language and may therefore have problems with texting type abbreviations.  I was able to figure out that you meant 'around' when you used the term 'ard' but others may not have done so. 

On the other hand I still haven't figured out what these sentences mean:

    "Nonetheless, it is a hell of a lot less than 120mA and any pulsed supply has to be good!"
    "They best way to go is probably to suck it and see by flattening the battery."


Don



I have attached the Datasheet.

And the LCD is powered by the Arduino which is powered by a 7.5V battery source..

And the multimeter I am using is similar to this: http://www.myflukestore.com/p1348/fluke_73-iii.php

Is there something wrong in the way I measure the current using the multimeter?
I connected the probes in series to the Vcc(the power pin) pin of the LCD display. And the other ends of the probes were connected to the ground and 300mA slots in the multimeter...

* LCD GDM2004D datasheet.pdf (737.32 KB - downloaded 36 times.)
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1mA is in the normal range for a text LCD display. 6mA sounds rather low for the backlight - perhaps you are using a series resistor that is higher than the manufacturer intended?
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Is there something wrong in the way I measure the current using the multimeter?
I connected the probes in series to the Vcc(the power pin) pin of the LCD display. And the other ends of the probes were connected to the ground and 300mA slots in the multimeter...

It could be the wrong meter.  I was merely speculating that such a low reading could be due to the supply being pulsed but, in that event, your meter may not be capable of properly reading it. If it is pulsed, not only does the power go off, but it is also likely to be off longer than it is on, and the meter is likely to have a hard time with that.

All that aside, the data sheet says the backlight current is minimum 150mA and I don't see any clear refrence to that supply being pulsed.
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Here are the original questions:  "So I am wondering, if I do not use the backlight, would I be able to extend the battery life significantly? If so, by how much?"

And now that we have the datasheet (specifically page 3/9) we can give better answers.  The LCD typically draws 1.5 mA while the backlight requires at least 150 mA.  That's a ratio of 100:1 so it appears that the answers are 'yes' and '100x'.

The reason for the 6mA reading is still a mystery.


Don
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Guys, a little off topic:

I have a confusion with a voltage divider rule, hope you guys could help.
It is over here: http://arduino.cc/forum/index.php/topic,161659.0.html
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