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Topic: LCD Backlight issue (Read 1 time) previous topic - next topic

econjack

The backlight on my TC1602A-09T sucks a lot of power and I'd really like to turn it off when the system's not being used. I've read almost everything posted here about backlighting but can't turn it off. The display does display my data correctly, cursor move and clear work fine. Pin 15 is the backlight power (+) and pin 16 is GND.

Now the caveats: I have over 30 years of C code experience, so I'm okay with the software. The hardware...not so much. I'm a newbie at the hardware stuff, although I do have it talking to the ATmega328 (Arduino), reading a DS1307 RTC and displaying its data, and taking input from a 4x3 keypad...all working great. (I've stood on a lot of shoulders getting this far...thanks to all!) But I'd really like to turn off the backlight when not in use. You can almost read a newspaper at midnight just using the backlight...that's got to be using a lot of power. I'd like to be able to run it for a few days on a battery if possible.

If I'm stomping on an earlier post, I'm sorry, but I really have looked around a lot. Any help would really be appreciated.

pluggy

You'll probably find the backlight uses less power than the arduino, but if it worries you, and you have a digital pin spare, you could use that to turn it off when you don't want it.  I measured mine which does a fair job of illuminating the room in the middle of the night and I found it used about 20mA at 5 volts.  

pwillard

It will ALWAYS be on if you supplied voltage to pins 15 and 16.  You cannot control brightness from the data pins... it's a totally isolated module... heck, it's just a bunch of LED's.

The way most people do it... is they insert a transistor... like maybe 2N7000 NFET  or 2N2222 NPN and control the cathode (K or the one you have to GND) pin on the back light and control that with a spare data pin on the Arduino.  

econjack

I'll give that a try. Thanks!

Jack

econjack

Pluggy:

Actually, that's a little less current than I expected, given the light it throws out, but I'm going to try that before I try Willard's suggestion.

Thanks!

liudr

Jacking the post along a different direction, has anyone used PWM pins to light up back light at different lumination? I heard that it is what lcd screens do to adjust brightness.

pwillard

since it is just a cluster of LEDs... PWM should not be a problem.

I also disagree about it not being much of a load on a pin... you need to ISOLATE it drive it with a higher current device... unless you don't mind having fewer pins on your arduino.

floresta

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You'll probably find the backlight uses less power than the arduino...


Quote
Actually, that's a little less current than I expected, given the light it throws out...


I hope you measure the current that your backlight draws before you try driving it directly with an Arduino pin.  I looked at a random data sheet and saw a typical backlight current of 180 mA.  That's almost 5 times the current rating of an Arduino pin.

Don

econjack

Yep...all is well.

BTW, when I upload a sketch to the Arduino, the LCD cycles in sync with the upload LED on the board. What is the Arduino IDE doing during the upload to cause this? Does it have a meaning, or is it just a byproduct of the IDE? Just curious.

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