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.

This topic has a solution.

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.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

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:

 

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Mon. Dec 3, 2018 - 05:25 PM
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That is pretty.

 

BUT...

 

With those long leads, I'd be uneasy about about using it with an oscilloscope (ringing and such, as in msg #1). Logic Analyzer might be OK (my Saleae LA just has wires with little grabbers on the ends).

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Nice!

It's listed as a 'Led BDM Frame':

https://www.aliexpress.com/item/...

 

Surprisingly pricey but (of course China ...) there is a budget version:

https://www.aliexpress.com/item/...

 

Apparently BDM stands for Background Debug Mode. The frame is used for debugging and programming in circuit processors in the automotive world.

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ka7ehk wrote:
With those long leads, I'd be uneasy about about using it with an oscilloscope (ringing and such, as in msg #1).

from TEX-QP - "QuickProbe" Probe Holder for SMD Test Connections

A less expensive way is to rig flex tube like what a quadriplegic has to attach equipment to their chair; what CNC milling shops use to direct fluid to cutting heads :

ModularHose.com - Loc-Line Modular Hose System

Can patch BNC jacks onto the PCBA then connect probes via a TEX-BA - BNC to Probe Tip Adapter

 


via Tyrosys Corp is a qualified small, Veteran-owned Texas Corporation.

 

"Dare to be naïve." - Buckminster Fuller

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Tonn wrote:

Surprisingly pricey but (of course China ...) there is a budget version:

https://www.aliexpress.com/item/...

 

This thing looked really useful. Alas the budget version doesn't include the frame part. It's just the probes. Wouldn't be too tricky to drill a bunch of holes in some perspex though!

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Some time ago I bought some plastic clamps, thought they were handy.

They had plastic swivel feet on the end, which fell off quite easily.

This left some V-groove shapes which quite solidly grab my round scope probe.

This makes a triangle with the 2 legs and the tip of the probe an can be placed quiete easily.

The pcb in the background is a "Blue Pill" with a QFP with a pitch of 0.5mm and it's quite easy to place the scope probe on one of the pins, though I tend to need a magnifying glass for such things.

 

Some words about the labels:

These are extremely to make in some spreadsheet program (i use libre office). Start by typing some lines of text for your labels, then set the row height to 2.54mm (Yeah weird number, I know, but it works :).

Then decrease the font size untill the text fits in it's allocated space.

Bold text works best for these small letters. you can also play a bit with left / right alingment etc.

Then print your labels on a piece of paper and stick some clear tape over it and then cut them out with a knife or scissors.

There are no flat spots on the Blue Pill to stick the labels to, because the header pins stick out on the top, but no worries.

Just apply a thick enough layer of hot snot over the pins to level everything out.

Then put the paper with the labels in the hot snot and press it gently with something flat such as a ruler untill the snot cooles down.

Alignment of the labels is best done if you put the Blue Pill into a breadboard, then you can align the labels with the breadboard holes.

 

Also, sorry for the blatant advertizing on the blue PCB.

I should have edited that out, as I usually do.

I do not like those PCB's much anyway because:

1). The advertisement text wastes room which could have been used for 4 more rows of holes.

2). All holes on the outside are connected together, wich is also effectively wasted board space.

    When building prototypes drilling a 5mm hole into the pcb for 100 or so wires for a big fat star ground is much better.

3). These PCB's out gass a lot during heating / soldering. Your solder tends to start bubbling.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Tue. Dec 4, 2018 - 03:19 PM