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[on:]

Hi there,
after experimenting with a LCD on my Arduino UNO  the Arduino board does not auto-reset when I plug in my USB cable. I have to push the reset button manually or (re)upload the sketch again. Even opening the serial monitor works fine to start the sketch again. When I tried to connect the LCD for the first time the UNO turned off (power LED slowly fading out), when I disconnected the ground cable again the Arduino turned on again. Do you guys know what that means?
I found out that a cable wasn't soldered to the LCD properly. After I fixed it everything worked fine. Is it possible that a short circuit damaged the parts that provide the reset function? I'm sure that it worked before.
Thanks for any help.

[Reply #1 on:]

after experimenting with a LCD on my Arduino UNO  the Arduino board does not auto-reset when I plug in my USB cable.

"Auto-Reset" in the context of Arduino means the existing sketch restarts from the beginning.  Is this how you are using "auto-reset"?

When I tried to connect the LCD for the first time the UNO turned off (power LED slowly fading out), when I disconnected the ground cable again the Arduino turned on again. Do you guys know what that means?

This means there was a short circuit somewhere.

There are two very bad practices mentioned here that you should avoid:
1.  Do not disconnect Ground, disconnect Power.  Ground is important.
2.  Do not change connections while your circuit is powered.  This will eventually lead to a mistake that will cause damage.

[Reply #2 on:]

after experimenting with a LCD on my Arduino UNO  the Arduino board does not auto-reset when I plug in my USB cable.

"Auto-Reset" in the context of Arduino means the existing sketch restarts from the beginning.  Is this how you are using "auto-reset"?

Yes, that is how I understand the function. If I start the serail monitor or push the reset button, the sketch restarts. If I just plug in a cable it does not.

When I tried to connect the LCD for the first time the UNO turned off (power LED slowly fading out), when I disconnected the ground cable again the Arduino turned on again. Do you guys know what that means?

This means there was a short circuit somewhere.

There are two very bad practices mentioned here that you should avoid:
1.  Do not disconnect Ground, disconnect Power.  Ground is important.
2.  Do not change connections while your circuit is powered.  This will eventually lead to a mistake that will cause damage.

Thanks for the advice. I'll keep that in mind.

[Reply #3 on:]

Okay, so that is not an "auto-reset" issue.  Plugging in the USB cable does not trigger auto-reset.

Instead, you have a "start" issue.  Does this also occur when no other hardware is connected?  (You may need to program the blink sketch to verify, so you can actually see something happening.)

[Reply #4 on:]

Hi James,
thank you very much for your help so far.
Ok then, let's call it a "start" Problem. Sorry for misleading you.
I disconnected all the hardware and tried the blink sketch - works fine!! Thanks. The funny thing though is that the "problem" always occurs when I connect the display (5v/ground), even with the blink sketch. Is that some kind of normal behaviour of the Arduino. Seems odd

[Reply #5 on:]

Do you have a link for the display?  It suggests it is causing enough of a load to prevent the chip from coming out of reset (on initial power up) properly.

[Reply #6 on:]

Hi, I got this here --> http://www.sure-electronics.net/download/DE-LM010.pdf

Im no expert but at first sight everything seems normal , doesn't it?

[Reply #7 on:]

I don't think the LED backlight has a current limiting resister.   On power up it is probably drawing a significant amount of current (and damaging the backlight).

Try a 33-200 ohm resistor in series between the 5v and pin 15 of the LCD.  (or as a test, disconnect the backlight all together and see how the behavior changes.)

[Reply #8 on:]

I already tried to use a 100ohm and 240ohm resistor but the backlight is barely visible then, thats why I always used it without any resistors. It's just not bright enough with a resistor in series.
But as a test I just tried a 1.5k ohm resistor and there is of course no backlight visivle anymore. But the start-problem still occurs, EVEN with the backlight completely disconnected. So the backlight is not the problem.

My setup is the same as in a tutorial from ladyada.net --> http://www.ladyada.net/images/arduino/lcdtut/bigpicture.jpg

thanks again for your help