[ATMEGA] LCD PWM LED and Contrast

Hello,

Is possible to control LCD's(hd44780) contrast and backlight by PWM outputs in ATMEGA(8)? If yes , how to connect it?

Why would you PWM contrast? Once set it will stay there. For the backlight use PB3 (MOSI).

Ok, so Vo to 10k potentiometer. MOSI in my construction is for programming, I'm going to use PB1(OC1A) but I read somewhere that I must connect backlight via some transistor and some resistors - but what?

As you know the ATMEGA8 can sink only 10mA. The LED-backlight requires 100mA in some cases.

Connect a small N-channel MosFet (BS170) to the I/O port via a 100Ω resistor and connect the drain to the backlight cathode (-). Connect a current limiting resistor to backlight anode (+) according to display specifications.

MOSI is used for ISP in almost every application. Despite that you can use it during normal operation as a PWM output.

like that:

Boncuk

Thanks a lot.
I can use this same connect for contrast?

Pol said:

Thanks a lot.
I can use this same connect for contrast?

Click to expand...

hi,

I would not recommend that, the contrast would be a min or a max, so the LCD could be blank or black.
Use a 10K pot from +5V to 0v, wiper to contrast pin on the LCD. Adjust for optimum contrast

Pol said:

Thanks a lot.
I can use this same connect for contrast?

Click to expand...

Once again: Why would one want to adjust contrast more than once? You might of course adjust it to blank the screen or make it fully black.

But again: For what reason?

Some industrially manufactured circuits don't even use a pot for contrast adjustment. (saving space and reducing cost)

Using a fixed voltage divider resulting in a Vee of 0.3 to 0.4V will set the contrast as well.