Can Noise form a circuit , effect UART?

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#1
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Hi All

 

I have moded a PCB, with some additional wires to a connectors and switches.

 

The main PCB has a UART connection to a RF module(AVR+RF), where the main PCB would communicate to it, if its soldered on. In this case the module is not soldered on. 

 

To acknowledge if this module is connected, i simple TX a "HELLO" and I would get reply "HELLO".  I am aware that my reply message should be slightly different. 

 

With the module not attached i am a still receiving a  "HELLO". I have checked my PCB for any shorts, but this is negative. 

 

Can noise cause such behaviour?

 

 

 

This topic has a solution.

Thanks

Regards

DJ

Last Edited: Wed. Jun 30, 2021 - 11:15 AM
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djoshi wrote:

Can noise cause such behaviour?

 

Absolutely not!

 

In consideration of others, please RTFM!

This reply has been marked as the solution. 
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djoshi wrote:

Can noise cause such behaviour?

 

Not noise but crosstalk certainly can. The input impedance of an AVR pin is quite high so a small amount of leakage caused by things like flux residue will cause an echo.

 

The easy way to check is to put a pull-up resistor on the main AVR's RX pin and test again. Something like 10k will kill any leakage/crosstalk.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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With the module not attached i am a still receiving a  "HELLO".

Also, are you clearing the old buffer content, so that you aren't just looking again at the very last message rcvd?    

 

if you send out

grape

apple

lemon

do you see all three "ghosts"?

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Mon. Jun 28, 2021 - 03:15 PM
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Makes sense, i will give this ago.

 

This echo/cross talk only happens sometimes.

Thanks

Regards

DJ

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Yes, but there is no module on the receiving side, so it would be send a blank message, but should not get a response. This would be then acknowledged in my application.

 

I have also cleaned to the PCB, lets see if it occurs again.

 

 

 

Thanks

Regards

DJ

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Could also be capacitive coupling. Enable the week pullup on the input RX pin by setting the port to 1.

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markywb wrote:

Could also be capacitive coupling. Enable the week pullup on the input RX pin by setting the port to 1.

 

What causes this?

Thanks

Regards

DJ