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Monochron w/ RGB LCD
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Please be positive and constructive with your questions and comments.

Monochron w/ RGB LCD

by rexmac on Sat Mar 27, 2010 4:17 pm

Hello all,
I am looking for some help regarding the use of a common anode RGB LED backlit LCD with the Monochron kit.

I recently purchased the following 128x64 pixel RGB LED backlit LCD: http://www.crystalfontz.com/product/CFAG12864A-CFH-TA.
Link to datasheet: http://www.crystalfontz.com/products/g12864a/datasheets/876/CFAG12864ACFHTA.pdf

I compared the datasheets for this LCD and the one included with the Monochron kit, and, while I am certainly no expert, it appeared to be a near perfect drop-in replacement. Turns out that it was! :)

I soldered in some header pins to the RGB LCD, swapped it with the B/W LCD, and powered on the clock. I had to adjust the brightness and contrast, but the RGB LCD is definitely working. Yay!

At this point, the LCD is backlit red because pin 20 of the RGB LCD is the red cathode. Pins 21 and 22 of the RGB LCD, the green and blue cathodes, are just "hanging out" next to the female headers of the main board.

As I understand it, RGB LEDs can be controlled using PWM output of the microcontroller. While I think that would be extremely cool and a fun project, right now I am only concerned with achieving a purple backlight. So I need the red and blue LEDs on, right? Well, the red (LCD pin 20) is already on (see above). I thought that connecting the cathode of the blue LED (LCD pin 22) to the microcontroller's ground pin (MCU pin 22) would work, but no such luck. The screen's backlight remained red. :(

At this point I am stuck and looking for any help I can get.

Thanks
rexmac
 
Posts: 3
Joined: Sat Mar 27, 2010 3:25 pm

Re: Monochron w/ RGB LCD

by rexmac on Sun Mar 28, 2010 3:19 am

After playing around with the RGB LED backlit LCD some more (under low-lighting conditions), I discovered that the blue LED was lighting up. It was just very, very weak.

I eventually plugged the LCD into a breadboard along with a boarduino. With some testing I was able to determine that R2' seemed to be the problem. I removed it and replaced it with a snipped lead. I now have a true purple backlit LCD. :D
rexmac
 
Posts: 3
Joined: Sat Mar 27, 2010 3:25 pm

Please be positive and constructive with your questions and comments.