Black on Green LCD

Su Jin

A tutorial about LCD https://learn.adafruit.com/character-lcds/using-a-character-lcd says that the nice thing of the black on green LCD is you can remove the backlight, sometimes they don't come with one.

If some one know such kind of LCD would you please tell me if it is true.

over 10 years ago

0 Dennis Eichmann over 10 years ago

Guru 74080 points

Hi Su!

Yes, you can read the display without backlight, but of course it isn't that good as if it is on.

Here is one:

Or here:

Dennis

0 Su Jin over 10 years ago in reply to Dennis Eichmann

Intellectual 740 points

Thank you very much. Reading the display without backlight will be very useful for devices powered by battery as the backlight consumes more than ten mA.

0 Dennis Eichmann over 10 years ago in reply to Su Jin

Guru 74080 points

Yes, that's right - the backlight consumes a lot of power. But you can switch it on/off by adding a simple transistor that is controlled by a GPIO of the microcontroller. Just in case you want to (temporarily) switch it on in the dark or whatever.

0 Su Jin over 10 years ago in reply to Dennis Eichmann

Intellectual 740 points

Yes, that's a good idea. I think in practice it depends on the easiness of reading the display.

0 Dennis Eichmann over 10 years ago in reply to Su Jin

Guru 74080 points

If you connect the transistor to a pin of the microcontroller that the timer module can be routed to, you can set the brightness by using a hardware PWM. This also reduces your total power consumption.

0 Su Jin over 10 years ago in reply to Dennis Eichmann

Intellectual 740 points

I do not understand what you said very well, can you recommend me some thing about it to read?

0 Dennis Eichmann over 10 years ago in reply to Su Jin

Guru 74080 points

Maybe this article helps? It is not for the MSP430, but it explains the basic working principle of PWM brightness control. If you have any further questions, jusk ask.

Dennis

0 Dennis Eichmann over 10 years ago in reply to Dennis Eichmann

Guru 74080 points

And to get an idea of the MSP430's timer, you can have a look here.

0 Su Jin over 10 years ago in reply to Dennis Eichmann

Intellectual 740 points

Thank you very much for your kindness.
Su

0 Su Jin over 10 years ago in reply to Dennis Eichmann

Intellectual 740 points

Thank you.

0 Dennis Eichmann over 10 years ago in reply to Su Jin

Guru 74080 points

So means you understood how it works or anything not clear about it? Maybe just do some experiments. If problems occur, come back here and we will have a look at it.

Dennis

0 Su Jin over 10 years ago in reply to Dennis Eichmann

Intellectual 740 points

You are so kind I'm really appreciate it, and certainly I'll back to tell you if I understand its working principles once I finished my reading.
Su

0 Su Jin over 10 years ago in reply to Su Jin

Intellectual 740 points

Hi! Dennis Eichmann,

Based on the principles described in the recommended paper, and that the watchdog timer has been configured as an interval timer at other part of my project, I got a solution to adjust brightness of LCD backlight, by inserting into its power line a transistor, the base voltage of which was provided by a GPIO pin of the project MCU.

Below is the code, I have added enough comments, it's easy to understand.

/* following two are defined in head file */
int8_t brightness_contl;    //< 0, LCD was not in use, power OFF; in a writing string LCD routine it is set to 1
int16_t brightness_number;  //when it%3 = 0, power ON, = 1 or 2, power OFF, it is set to 0 along with brightness_contl  

P2DIR |= BIT6; 

/* the interval timer interrupt service routine */
void WdtIsrHandler(void)
{
        uint8_t working_variable;
	timeCounting ++;    //an interrupt is generated every 15.625 msec, added 1 to timeCounting 
	if (brightness_contl<0) return;
	working_variable = brightness_number % 3;
	switch (working_variable) {
	case 0: P2OUT |= BIT6; break;    //P2.6 is used, backlight ON 
	case 1: P2OUT |= ~BIT6; break;  //backlight OFF
	case 2: break;}                                //backlight OFF
	brightness_number ++;
	if (brightness_number>640) {brightness_contl=-1; P2OUT |= ~BIT6; }   //640*0.015625 s/count, after about 10 second, i.e. the string will stay only for 10 second 
}

I'm not sure if it's right, please take a look and give me a few words of evaluation.

Thank you very much.

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Black on Green LCD