Fade in and out LCD 16x2 : HD44780

Hi,

I have noticed that the LCD screen operating Temp must be > 0°c so I will have to power off it and on it when Ambient Temp reach 0°C.

I would like to make a fade effect in and out when I power on and off it.

Shall I use a RC circuit to do that ? (capacitor and resistance) to do this or soft ? (I prefer hardware auto fade that using lines code).

Have you got some links of RC circuit ? Thank you

You got the concept right but RC circuits have time constants = R*C. You will be getting a very fast fading that you can't even see, with typical values of R and C. You could use a digital potentiometer in conjunction with a regular pot. Then fade with the contrast through changing the digital potentiometer value.

Thank you liudr.

Have you got some links about it ?

I don't know digital potentiometer, how much is it cost ?

Maybe something like this:

http://www.maxim-ic.com/datasheet/index.mvp/id/2780

I have noticed that the LCD screen operating Temp must be > 0°c so I will have to power off it and on it when Ambient Temp reach 0°C.

The display will probably just become too faint to read when the temperature drops.

I would like to make a fade effect in and out when I power on and off it.

There is no brightness adjustment on the commonly available LCD modules. The only way you can get anything like a fade in or out would be by tinkering with the contrast (the voltage on pin 3) and the best way to do this is probably with PWM (pulse width modulation) on pin 3.

Putting these two thoughts together you could probably start out with a really cold room temperature and raise it when you want the display to appear.

Don

You will be able to use PWM to control the brightness of the LED backlight. The back light will draw more than 40ma, so you will want to drive it through a transistor like a 2n2222 or equivalent.

If you just want to cut power then you could add a capacitor in the backlight power lines and then it will dicharge, fading the backlight out. This won't work for fading in but just thought I'd throw it out there.

Mowcius

This shows how a microcontroller can control VEE which is contrast.

http://www.piclist.com/techref/microchip/pwmvee.htm

You can use a transistor to pwm the backlight or use an I/O pin to turn it on and off.

Once all of that is done and off you can kill power to the display with another transistor and I/O pin. Then to bring it back up you turn power on, VEE up and backlight on and send the LCD initialization routine.