Unwanted Resistance from Reset Pin to ground!!

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Give up and change the Micro

Well, I changed the ATmega128 with a similar MCU in terms of architecture, ATmega64!

I only changed the header file and also changed the chip setting in the project configuration!

It's working well, however I have not used it for a long time to see if there are problems! 

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I couldn't thank you enough guys! You all helped me a lot and I appreciate that!

I will inform you how my project goes!

yesheart

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ashoori1993 wrote:
By the way, I had my PCB electrically checked by the company, ...
Likewise with a colleague's power PCBA, internal short in PCB, fire (FR-4 resin will burn)

Otherwise, can locate shorts inside PCB by a microvolt meter (voltage drop between two nodes in a current loop)

 

"Dare to be naïve." - Buckminster Fuller

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N.Winterbottom wrote:

  1. Use a current limited power supply for testing.

Concur

Can also vary the voltage and observe correct reset behavior (some AVR will draw up to 1mA to exit reset)

Can DIY such.

 

The Art of Electronics 3rd Edition | by Horowitz and Hill

Download a sample chapter

[page 123, middle of right column]

9.13.3 Foldback current limiting

How to Protect Circuits from Overcurrent Spikes | onsemi (off in 5 microseconds)

 

"Dare to be naïve." - Buckminster Fuller

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Post a pic or pdf of the schematic  (not some unknown file) ...who knows what conditions you might have created

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

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Here is the schematic.
 

Attachment(s): 

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The problem is not solved yet!!

I changed the ATmega 128 with Atmega64 and modified the code to run on the new chip.
It was working fine for an hour, the I intentionally stopped it to do some changes in code, but after that it started to reset again!

This time even worse!

The voltage on the reset pin floats around 2.2 V and keeps the chip in reset mode! It even doesn't let the chip to startup at all!!

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Do you think tying the reset pin to VCC will be a good idea to deal with this issue?

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What happens when I push the reset button while the reset pin is tied to VCC? Does it make a short circuit? or better to say how bad will it be?

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Update:
I tied the reset pin to the VCC and it seems fine, but I'm afraid to use the reset button cryingcrying
 

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I tied the reset pin to the VCC

NO.

Don't do that.

 

The programmer has to pull the Reset\ pin low to program the micro.

Tying to V+ could damage your programmer, and in any event make it not possible to (re) program the micro.

 

You need to determine the problem, and solve the underlying problem, not try to force the Reset\ pin high.

 

JC 

 

Edit:

Check your 7805 Data Sheet, also.

 

One typically has a 0.1 uF cap on the output, close to the leads, in addition to your Cout cap.

Likewise, one often puts a 0.1 uF cap on the input side, or a 0.22 uF cap, again close to the regulator's leads, in addition to your Cin.

The "Big Caps" do not replace the need for the "Small Caps".

 

JC

Last Edited: Fri. Sep 10, 2021 - 09:22 PM
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Tying to V+ could damage your programmer, and in any event make it not possible to (re) program the micro.

Yes, you are right! I didn't know that until I tried to program the chip and my laptop disconnected the USB bus due to high current sink!

I removed both pull-up resistor and the short connection and instead I soldered a pin header on the pads! I put jumper on the pin header when I want to connect reset pin to VCC and remove it when I'm programming the chip! However it's just masking the issue.


I do your suggestions about capacitors and I will let you know how it goes.


By the way, I already considered several filters on the power line!


I'm using a 9V adapter, a 1000uF exactly on the output of the adapter, a regulator module as shown below and also 470uF cap at the output of the module, as well as 100nf caps close to the MCU

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In #3 N.Winterbottom wrote:
How do you know you haven't got a dodgy switch ?

 

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How do you know that it isn't a problem with whatever plugs onto the 'interface' connector? 

#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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ashoori1993 wrote:
I'm using a 9V adapter,
Some of the wall wart failure modes :

  • pass transistor shorts and there's no crowbar or clamp (cheap wall wart)
  • mis-wired connector (LM2596 won't survive whereas 78M05 will)

ashoori1993 wrote:
a 1000uF exactly on the output of the adapter,
Some wall wart datasheets state a maximum bulk capacitance (surge); some wall warts (cheap) lack current limiting.

 


PolyZen Device Fundamentals (Littelfuse, up to 15Vdc)

[page 2, middle of right column]

... a device may experience voltage spikes as high as 88.5V (141V p-p) when connected to a poorly regulated, third-party charger.

 

"Dare to be naïve." - Buckminster Fuller

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How do you know you haven't got a dodgy switch ?

I have a reset button on my PCB and a few buttons on my interface including reset button, some interrupts and a few general purpose keys.
To check this assumption, I disconnected the interface connector and also removed the reset button from the PCB so there were no keys at all, so faulty switch isn't probable! 

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The conclusion of what you said is to replace the regulator module and to consider replacing the adapter with one which has current limiting!?

By the way, It also can't be because of the code! first I thought maybe some interrupts occure at the wrong moments or at start-up forcing the chip to reset, but even erasing the chip didn't solve the issue!I mean the chip with no code running! it had floating voltage on the reset pin, too!

Last night I tied the reset pin to the VCC and it worked fine! It worked for 9 hours until I turned it off to check the logged data, but in this case I don't have the reset button(or I'll probably damage the chip if I push the button sad)!

If it was my own project I would compromise, but It's a teamwork research project and everyone has contributed at his finest, so I will be responsible for any possible flaws (I guess!!)!

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ashoori1993 wrote:
Here is the schematic

 

Missing 100nF at Oscillator.

 

Your ATmega does deserves a linear regulator. Think about it. Google lm2596 dc-dc spikes.

 

I then monitored the output of the step down converter closely with oscilloscope, all looked fine, but after setting time base to 25ns, I could see that at the moment when connecting the input voltage to the step down regulator, its output VCC spikes to plus 18V and down to minus 10 volts, but only 25-50 ns in length, and then back to 5V.

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ashoori1993 wrote:
The conclusion of what you said is to replace the regulator module ...
LM2596 may be damaged ... or not; an oscilloscope can record Vin, VCC, and RST (is there a correlation between RESET, an anomaly on some mega128A output signal, and VCC?)

AVR can be upset by ESD/EMI/EFT/lightning or by a power supply's instability (regulators are typically conditionally stable)

Meanwhile, recommend LM2596 IN+ to D1 cathode.

ashoori1993 wrote:
... and to consider replacing the adapter with one which has current limiting!?
and crowbar or clamp.

First, replace that power adapter with an unconditionally stable power supply (automobile battery, some motorcycle battery)

Second, replace that power adapter with a one of increased quality; AoE power supply noise testing had these warts :

  • CUI 9V 20 watt desk-wart SMPS
  • Jerome RYD313F-001 15 watt triple desk-wart linear
  • Apple 10 watt USB SMPS
  • CUI DV9500 unregulated 9V 500 mA wall-wart

Because J1 (Power Jack) is common then a power adapter issue will return; recommend external to the power adapter - current limiting and voltage limiting (PolyZen)

Operators have a tendency to forget to pack the device's wall wart or desk wart (so, operator substitutes)

 


The Art of Electronics 3rd Edition | by Horowitz and Hill

Download a sample chapter

[page 14, middle of right column]

8.15 Power-supply noise 578

[page 120]

9.13.1 Overvoltage crowbars

...

We’ve encountered some aberrant bench supplies that soar to their full output voltage, briefly, when you switch them off. But “briefly” is all it takes to ruin your whole day!

 

"Dare to be naïve." - Buckminster Fuller

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Why would you bring in an external signal without any protection, or at least 100 ohm  or 1K resistor???  You are just begging for a blowout, should anything external short to 12v, even for a microsecond.

 

A thousand ohms might not allow an unending short, but is much better than division by zero.  A quick zap from a slipped screwdriver or dropped wire strand will become just be a laugh.

 

   

 

I always include 200 ohms in any TX or RX line that goes off board....gives a lot of leeway in case of accident.  Also protects the PC (somewhat) should there be a 12V short on the AVR board, though I almost always use an isolator. as pure protection   The 200 ohms isn't an issue, unless perhaps you are at warp serial speeds or driving a bunch of capacitance.

 

 

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

Last Edited: Sat. Sep 11, 2021 - 06:45 PM
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I noted curios /to me/ use of 10 ohm resistors in Vcc line, to many places in some (TV) electronic board, with a duty to protect a single chip, together with 10-100uF cap.

Such small resistor is also a fuse, if the chip goes puff, the resistor will break and protect the rest of Vcc (5V or else) onboard.

There is no security signs whatsoever in OP board, sorry.

Last Edited: Sat. Sep 11, 2021 - 06:29 PM

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