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Author Topic: (Solved)New I2C LCDs wont work  (Read 1779 times)
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alabama
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Hello Aeduino Forum,
That is what my new LCDs are supposed to read with the example from fm's new Liquid crystal library.
Just get lightly blinking backlight and the custom characters jumping around on line one.
Only four wires, checked them 20 times, tried different Ardy's, found a I2C lcd library made especially for the chips on the I2C breakout, got nuttin'. The address is right, tried a bunch of others and didn't get a glimmer. Tried both 4.7k and 10k resistors to grnd from the slc and sda pins, i at least got a steady backlight but nothing else with either value. Also tried 3 of the LCDs all act the same.

I am using the old wire.h library, I have read it is flaky.
Any other suggestions?
TomJ
« Last Edit: June 22, 2012, 08:56:26 pm by Tumbleweed » Logged

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Hi TomJ,

which LCD I2C backpack are you using?
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alabama
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FM,
Some Chinese knockoff, from GE Tech, the I2C chip on the back is a PCF85747. Next line is K63331, but that is usually a date code.
I found am I2C library that said it was for that chip on the Playground, but even with the right address and their code I got nothing. No
blinking backlight no lightly scrolling characters.
 The contrast needed adjusting to see the characters at all on your code, but that is usual.
By the way how do I positively turn on the backlight with your library and a I2C controlled backlight?
Thanks,
TomJ
 
« Last Edit: June 22, 2012, 06:14:24 pm by Tumbleweed » Logged

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Hi TomJ,

that chip is very much like the one I use on my backpack: the NXP PCF8574A
The library is well qualified with that chip and should work out of the box if you/they haven't changed the I2C address mapping.

The contrast is adjusted with a trim pot. Do you have a picture of the backpack or a schematic?
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alabama
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I think I can get a picture, but it isn't much good.



Thanks again
TomJ
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alabama
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I don't think that is the actual product, mine has no Aduino logo on it.
Just click it and open in a new tab. Just www.geeetech.com.
Here is a link to the product, haven't gotten the .rar document to open yet, but i will.http://www.geeetech.com/arduino-iici2ctwi-1602-serial-lcd-module-display-p-498.html
TJ
« Last Edit: June 22, 2012, 06:56:57 pm by Tumbleweed » Logged

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alabama
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OK,
Tried their library, just got compile errors in Arduino 1.0.1.
"
In file included from HelloWorld.cpp:3:
C:\Users\Tom\arduino\arduino-1.0.1\libraries\LiquidCrystal_I2C/LiquidCrystal_I2C.h:81: error: conflicting return type specified for 'virtual void LiquidCrystal_I2C::write(uint8_t)'
C:\Users\Tom\arduino\arduino-1.0.1\hardware\arduino\cores\arduino/Print.h:48: error:   overriding 'virtual size_t Print::write(uint8_t)'
"

Going back to FMs, and try more stuff. Good thing I'm retired, I could have ordered good ones for all the time I've spent.
TomJ
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If their library (the one you linked to) matches the hardware you have then in order to use fm's library you will have specify
all the bits for the i2c pins because they are different from the default pin mappings.
(The nibbles are flipped).

So when using fm's library you will need this constructor:

Code:
LiquidCrystal_I2C lcd(0x38, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);

This should set up the proper pin mappings and the pin mapping and polarity for backlight control.

If you want to use the examples, you will need to modify the constructor.

--- bill


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alabama
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Thank you so much Bperrybap,
It works fine now.
All I had gotten done was making the backlight stay on with the playground library.
Guess I will  have to put that in each sketch?

Thanks FM for the library and examples too.
TomJ
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