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Topic: Tx pin problem (Read 2178 times) previous topic - next topic

000

Hi all,
From today morning My arduino board Tx pin always is lit up... It shows a voltage of ~3.6V. I havent used a serial.print commands. Even Blinky codes cause Tx pins to go high... Is it the problem with the ATMEGA328 IC? because it was working fine till yesterday... Any way to rectify this?? Wat all could be the possible reasons why this Tx pin is showing continuous HIGH?
Hoping for a fast reply :)

James C4S

If you have a scope (or frequency counter) you will be able to tell if the pin is staying HIGH or if it is toggling faster than you can see.  Only being 3.6V suggests it is toggling.

If you take the chip out and the LED stays high, it would suggest it isn't the ATmega328.
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000

I dont have a scope. :(
It should be ATmega328 I guess. taking the chip out causes it to stop being high... Any suggestions?

000

I guess it is. I put in a new atmega328 IC and it stops Tx being high... So any way to repair the old chip? because it works fine except for Tx being HIGH.

000

the problem is back even with new IC. any help on this?? Cant I declare Digital pin 0 to output? still watever code i run its now showing a voltage of 5V. :( What could be the problem??

retrolefty


the problem is back even with new IC. any help on this?? Cant I declare Digital pin 0 to output? still watever code i run its now showing a voltage of 5V. :( What could be the problem??


A couple on points. First the board's TX led is driven by the on board USB serial converter chip (either FTDI or 8u2 depending on what specific arduino board you have), so if it's continously lit that could indicate something other then the 328 chip. Next the USB serial convertor chip while idle normally puts out a +5vdc high to the arduino pin 0 via a series wired 1k ohm isolation resistor. If you are not using serial commands you are free to set pin 0 mode to output and set it to LOW as that will have no problem overridding the HIGH from the serial convertor chip.

So can you upload sketches to your board, like blink? What are you wishing to do with pin 0 on the arduino?

Again what problem(s) are you trying to solve? And you really should post the code you are trying to run to show us what problem you are having.

Lefty

000

Quote
So can you upload sketches to your board, like blink? What are you wishing to do with pin 0 on the arduino?

Yes. I can. But  the problem is even the blinky code on any pin say pin 10 works... but still the Tx pin remains at high state...

I am trying to use pin 0 as a normal output pin. and I am not using serial commands... If u ask me will the pin 0 work? it works. because if i explicitly make it LOW if a particular condition is met Pin 0 output becomes zero. But the problem is when its in standy or not doing any operation on pin 0 like in blinky  code on pin 13, Tx pin it goes high for no apparent reason.

I even tried setting Output to LOW in the setup function thinking that default value of Pin 0 may be HIGH and I will set it to LOW once in setup so that it low whwn rest of the program runs. but still Tx pin goes HIGH. :(

and Currently its showing a voltage of 3.6V. :( 

retrolefty


Quote
So can you upload sketches to your board, like blink? What are you wishing to do with pin 0 on the arduino?

Yes. I can. But  the problem is even the blinky code on any pin say pin 10 works... but still the Tx pin remains at high state...

I am trying to use pin 0 as a normal output pin. and I am not using serial commands... If u ask me will the pin 0 work? it works. because if i explicitly make it LOW if a particular condition is met Pin 0 output becomes zero. But the problem is when its in standy or not doing any operation on pin 0 like in blinky  code on pin 13, Tx pin it goes high for no apparent reason.

I even tried setting Output to LOW in the setup function thinking that default value of Pin 0 may be HIGH and I will set it to LOW once in setup so that it low whwn rest of the program runs. but still Tx pin goes HIGH. :(

and Currently its showing a voltage of 3.6V. :( 


Again, if pin 0 is in it's default input pin mode you will still measure +5vdc on it because it's wired to the Tx pin of the serial USB convertor chip. I think you are making out a problem that is not a problem. Why must you not want to see a positive voltage on pin 0 if you are not using it?

Lefty

000

Quote
Again, if pin 0 is in it's default input pin mode you will still measure +5vdc on it because it's wired to the Tx pin of the serial USB convertor chip.

but I explicitly made it a Output Pin. So it must behave as a normal output pin right??

Quote
Why must you not want to see a positive voltage on pin 0 if you are not using it?

Well I am connecting a led to that pin so i dont want it to be ON everytime. I need to make it HIGH and LOW according to certain conditions.. and I usually want it to be LOW. So wont specifying a the pin to LOW in setup function solve the problem? Apparently it is not... :(

retrolefty

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So wont specifying a the pin to LOW in setup function solve the problem? Apparently it is not...


In setup change the pin to output mode, then set it to digitalOut low, problem solved, no?

Lefty

000

Quote
In setup change the pin to output mode, then set it to digitalOut low, problem solved, no?


I have already tried that. Apparently it doesnt work for me. :( Logically it ought to but it aint working. :(

000

I want to whether there is some statements other than Serial commands which might trigger the pin 0 to go high randomly.

retrolefty


I want to whether there is some statements other than Serial commands which might trigger the pin 0 to go high randomly.


You have me stumped. Other then posting your complete sketch that exhibits the symptom, I can think of nothing else to suggest.

Lefty

000

I dont why.. but now it goes low when I put it to LOW in setup... weird...  :smiley-roll:
Anyways thanx for the help :)

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