Hello!

Is it possible to use the PWM output of a PIC to controll the contrast of an LCD? (into pin 3 of lcd)


Thank you!

 

Yes, you may need a lowpass filter to generate a stable DC voltage, but it's a commonly used technique (to allow contrast adjustments via the processor).

Personally I've never tried it, I'll be interested to hear how you get on, particularly if you need a filter or not. I'm sure you'll be able to find something about it on the net, maybe even in the MicroChip application notes somewhere?.

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Finally I got my LCD to work :þ
Had some problems to get it to work with a 887, so I swiched to 628. Now it works. (yes, your tutorials (: )

Now I will start experimenting with the contrast.

 

OK my initial tests show that filtering is definately required.

Here are som pics. There is some distortion that doesn't show well on these pictures.

Attached Images

	lcd_004.jpg (71.6 KB, 849 views)
	lcd_003.jpg (77.5 KB, 848 views)
	lcd_002.jpg (75.5 KB, 849 views)

 

Here's a clip to show it.

(forgot to turn off the music)

http://removed.link

 

That's pretty cool. 8) What was the PWM rate for your contrast signal? And what kind of filtering did you have to apply?

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100% is 100% PWM and 0% is 0% PWM, so actually it should say 'PWM' instead of 'Contrast'

I did some experimenting. Used a 330ohm and 10µF as a lowpass filter. It showed some distortion on higher PWMs. After increasing the capacitor to 100µF the distortion dissapeared. So a capacitor between 10µ and 100µ would be optimal.

 

Your thoughts? (nigel? )

 

Well I loved the video!, even the music was quite amusing :lol:

It looks like you have the situation well under control, from your tests it looks like a filter is essential.

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PIC programmer software, and PIC Tutorials at:
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Actually, I just meant the wave period in general. Was there any flickering that was noticeble to the naked eye?

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Umm... YES! as you can see from the pictures (without the filter that is).

Or am I not still understanding your queston?

 

That's a pretty cool enhancement you made. Never thought of using PWM for the contrast before.

 

It's common commercial practice, many items use it.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk