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Support Forum » LCD only displays bars in rows two and four

December 08, 2012
by keith712
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i lent my nerdkit to a friend so they could use the device with a program i had written. i got the kit back a couple days later with my friend saying, 'it broke.' it turns out all the components on the breadboard will program and run a program just fine but the LCD only displays bars on rows two and four no matter what the mode (program or run) and no matter what i try to do to it from a program. anybody know what's going on? do i need a new LCD?

December 09, 2012
by Ralphxyz
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Hi Keith, first thing pull all of the wires and re-do it.

There are lots of discussions about two black bars here in the forum.


December 09, 2012
by keith712
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thanks Ralph... i found a couple black bar forums and read them... after the read i completely rewired the LCD with all new wires... i took the time to do a much neater job with color coding for control, data, power, ground and contrast leads but to no avail... i didn't press my friend for details but i think he dropped the kit...

anyway after the rewire i still only get two bars... i also hooked up the LCD to a second kit and still the same two bars... i'm going to purchase a new LCD because i want/need one and maybe i'll try to write a program to 'test' the 'broken' LCD... does a nerdkit have enough power to run two LCDs simultaneously?

December 09, 2012
by dvdsnyd
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Have you tried to reprogram the chip? I had something similar happen once. I think I may have accidentally supplied unregulated power to the chip. and it erased the program. Something to try anyways. The components are pretty resilient.

Not sure about 2 LCD's There is plenty of power, but...One LCD pretty much takes up 2 full ports. You wouldn't have but a few pins available for other things. You could look into Rick's I2C LCD project. This would allow you to be able to control 2 or more LCD's using only 2 digital pins for both displays combined.

Good Luck!


December 10, 2012
by keith712
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hi David, i did reprogram the chip with a version of led_blink which i modified to both blink two LEDs and display on the LCD information about which LED i was blinking and how many times it would blink and the rate of blinking... the LEDs blinked per my instructions but the LCD only displayed the two bars...

i think the I2C LCD project is really trick but is way too sophisticated for me at this time...

now that i know there's enough power (thanks) i was thinking of copying the code in the libnerdkits/lcd.c file and modifiying it to write to an LCD connected to some combination of the PC0-5 and PB1-5 port pins on the opposite side of the ATmega168 from an LCD connected to PD2-4, PB7 and PD5-6 per the nerkkits instructions... once i have the program debugged i could write the same message to both LCDs and compare the displays... actually now that i think about it i'm not sure what i would learn about the 'broken' LCD but this may be a good project to learn more about the C language which i'm still struggling with...

my new LCD should ship soon... wish me luck... k

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