Solved: Is an overshoot of 2.0V normal for an ATiny85?

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Hi,

I am experimenting with an ATtiny85, running a simple blink program written in C.

 

I noticed the output having an overshoot of 2V, followed by an undershoot of 1.5V and some ringing.

Is that normal?

 

Power decouple cap 100nF (85.6nF measured), load 3mA (1k resistor and a red led).

I already tried changing the load, changing the output pin, changing the chip, removing all connections as much as possible, adding an elco of 10uF for extra decoupling.

Thanks.

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Last Edited: Sun. Dec 2, 2018 - 12:55 PM
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Tonn wrote:
I noticed the output having an overshoot of 2V, followed by an undershoot of 1.5V and some ringing. Is that normal?

 

Where is the ground of your scope located?

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How did you determine/measure the overshoot?

- Brian

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ki0bk wrote:
Where is the ground of your scope located?

Overlooking the obvious ....

 

I did something I never do.

I measured on channel 2 of my scope, using the ground of the channel 1 probe.

 

Sorry guys and thanks.

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In a company I worked for whe had some custom jigs to maintain signal integity while measuring with a scope.

One of those was a simple piece of Teflon Coax with a BNC on the other end.

The hot end of the teflon Coax was just the center and the GND wires which were to be soldered directly to the PCB test points.

 

But for simple measurements I tend to limit the scope bandwith to 20MHz or less.

This makes a lot less forgiving for non critical measurements (such as blinking a led) and usually limits the view on screen to stuff you want to see.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Thanks for the tips.

I must admit I never even considered soldering the test leads and have always kept on fumbling with probes and clips.

 

Teflon: is that for the soldering heat or for the flexibility? Or do you just mean RF?

Last Edited: Sun. Dec 2, 2018 - 03:04 PM
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I the Teflon worked great for soldering, the exposed wire was just around 2mm and the wires could be soldered repatedly without anything melting.

Just every now and then the copper fatigued and broke off and then you had to strip a few mm of the cable again.

It was for making final adjustments on RF circuits, and I do not know if Teflon was also used for (lack of) interference with the RF signals.

I did mostly audio reated stuff there and sometimes helped out in the RF department.

 

Some time ago I found a test jig on Ali (I think) and I saved the picture.

It looks beautifull, is easy to make yourself and it looks usefull too: