EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: @rt on August 14, 2016, 04:02:38 am
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Hi Guys :)
I’m making a breadboard to try using a graphic LCD display for the first time.
The LCD I’ve chosen is this one: https://www.sparkfun.com/products/710 (https://www.sparkfun.com/products/710)
... and here is it’s pinout from the data sheet:
(http://img.photobucket.com/albums/v186/ArtArt/LCD_Pinout_zpsag6af53x.png)
I’m familiar with all other pins from using character LCDs, but hoping someone can better explain the purpose of pins 3 & 18.
Usually, pin 3 is for a variable voltage to adjust LCD contrast with a pot used as a voltage divider, but then what is pin 18 for?
The product page on the Sparkfun site has a Pong Clock project, and I see this in the schematic:
(http://img.photobucket.com/albums/v186/ArtArt/GFX_Schema_zpszdexhcm1.png)
Is that a mistake? Because that’s just a fixed 10k resistor with the wiper connected to nothing.
Cheers, Art.
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128x64 LCDs require around 8V to operate.
Vee is the output of an inverting chargepump: Vee = -Vdd = -5V.
The voltage is taken from Vee and divided using the contrast pot between Vee and +5V so you can adjast the contrast voltage at pin 3 to around -3-4V.
The pot at the Pong Clock is connected wrong.
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Thanks for the clarification :)
Some other schematics on the net suggest the same.
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The two 4k7 resistors top left is my pot :D so far I have it wrong ;)
Other than that, the two supplies are good, and the backlight works,
so I think tomorrow I get to program.
(http://img.photobucket.com/albums/v186/ArtArt/GFX_LCD_zpsmhrex3xy.png)
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Here is a good reference for these, they have several pinouts:
http://playground.arduino.cc/Code/GLCDks0108 (http://playground.arduino.cc/Code/GLCDks0108)
It has some of the various pinouts.
I have a couple of displays that use the KS0108 controller chip.
The Vee pin on my modules is a negative voltage input, not output.
It was from Amazon.com by NKC.
This explains why they were cheap, external -Vee required.
I needed a 9V battery connected "backwards" to Vee and the contrast pot.
Most don't.
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I’m trying to make a fixed resistor divider that works. For now, 4k7 + 390R is working.
Hopefully later, the dsPic can make a PWM output to adjust contrast digitally.
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It’s fun to catch up after these LCDs have been out for years!
Just the character data I’ll have to rotate once at startup.
I figure I need to up the value of both resistors, because there’s supposed to be at least 10k resistance from VEE to the supply,
but I have a total just over 5k.
(http://img.photobucket.com/albums/v186/ArtArt/Character_Test_zpsqiwmusv0.png)
https://www.youtube.com/watch?v=ahKH19iN2SM (https://www.youtube.com/watch?v=ahKH19iN2SM)