LCD pin layout testing

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young_student
 
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Joined: Mon Aug 08, 2011 8:17 pm

LCD pin layout testing

Post by young_student »

I got this old Sharp LCD that is based on HD44780 controller chip:

Image

Since it is EL foil back-light i decided to "upgrade" to LED based one. So i bought GDM2002D LCD board based on KS0066U controller. For some reason i get no characters at the output - on the new one. Tried adjusting contrast via 10k trim but no help (no characters at all appear). I got the spec sheet for the new GDM2002D display (interface pin connections) however i got no info on my previous one.

Both units have standard pin layout 14 pins (+ additional 2 for the LED element on the GDM2002D) in two rows. After determining pin 1 on the new unit i connected other pins the normal way (i.e. pin3 contrast, pin4 register select, pin5 read/write, etc.) but no characters at the output. :(

I'm wondering is there a way to determine the pin layout of my old LCD via oscilloscope. Because i suspect the layout might be different. I tested with a multimeter, and pins 1 and 2 on the old unit are power supply, while the pin 3 is contrast adjustment. So far appears ok, but when connected, i get a no go.

I got no idea what to expect to see on an oscilloscope when testing pins 4-14 on the old LCD board (to determine if they are the standard LCD layout).

Any help appreciated!!!

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zener
 
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Joined: Sat Feb 21, 2009 2:38 am

Re: LCD pin layout testing

Post by zener »

It could just be a difference in the contrast voltage (Vo)

young_student
 
Posts: 3
Joined: Mon Aug 08, 2011 8:17 pm

Re: LCD pin layout testing

Post by young_student »

Thanks! I will give it another shot.

young_student
 
Posts: 3
Joined: Mon Aug 08, 2011 8:17 pm

Re: LCD pin layout testing

Post by young_student »

Ok bought another LCD. WH2002A based on KS0066. Same problem. All i get is: either empty screen or filled blocks - depending how i adjust the contrast voltage. But no characters at all appear.

Seems like Sharp LCDs based on HD44780 are not compatible with KS0066 controllers despite some of the internet myths. My example proves it. Leaving this post for the archives.

Bye!

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