Reset pin problem

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Hi !

On few ATZB-A24-UFLB modules that don't work properly I've noticed that voltage on RESET pin slowly drops from 3,3 V to 0,5-0,3 V in 10-15 seconds and module stops to work.

What might be a problem?

Has someone experienced that?

Thank you and regards !

Last Edited: Fri. Oct 16, 2015 - 02:04 PM
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Reset is an input without internal pull-ups, and as such it should be connected at least to a VCC rail (via a resistor). It is better to use an RC-chain to provide a proper reset pulse.

NOTE: I no longer actively read this forum. Please ask your question on www.eevblog.com/forum if you want my answer.

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alexru wrote:
Reset is an input without internal pull-ups, and as such it should be connected at least to a VCC rail (via a resistor). It is better to use an RC-chain to provide a proper reset pulse.

Got that all.

I've noticed that this problem:

Quote:

On few ATZB-A24-UFLB modules that don't work properly I've noticed that voltage on RESET pin slowly drops from 3,3 V to 0,5-0,3 V in 10-15 seconds and module stops to work.

rises during powering ON the module.

Now reset pin is on 0,9 V and drops to 0,3 V and keeps "floating" on 0,3 V.

Sometimes module starts working OK(I can see that by LEDs) but soon after that it collapse (doesn't respond to USART and other).

I suppose some problem with innitial conditions, maybe ?

Thank you Alexru!

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It makes no sense to measure voltages on a high impedance input, you just measuring some stray charge that can depend, for example,on humidity of your room. And it can change over time.

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Hi again!

As this happens during powering ON does this have some kind of connection with BODLEVEL fuse bit maybe?

My Brown-out Detection is disabled.

Thnx Alex!

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What? That voltage on the floating pin is unpredictable? No, it has nothing to do with anything, it's just how electronics works. You will see this effect on any pin floating pin, not just reset.

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Seems I wasn't clear enough, sorry.

Module that had problems with floating RESET is working fine now. I left it POWER OFF for some time and it works OK now and RESET is 3,3 V.

I was thinking that during powering ON voltage is not stabilized (or something like that) and while the uc is "rising" voltage suddenly drops and uc gets stuck somewhere in stack.

I ran into this situation(module doesn't work, acts strange) when I turned it ON/OFF several times in short period(2-3 seconds).

BODLEVEL fuse bit should be disabled?

Thnx !

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You are still measuring voltages on a reset pin that is not connected to anything externally?

I do not understand what is going on. Can you show your schematic?

If it is acceptable in your application, always enable BOD.

NOTE: I no longer actively read this forum. Please ask your question on www.eevblog.com/forum if you want my answer.

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Sorry for keep you waiting. AVRfreaks was down for some time.

Here is my schematics. It's my 5th version now. I had some problems with hardware design before but 4th version is similar to 5th and I think it's OK.

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