[SOLVED] Ringing in the edges of a quare wave

Orson Cart said:

Hello Boylesg, scope probes can give overshoot or under shoot but rarely real ringing (several cycles), on breadboard - the extra capacitance on this medium is notorious for extra effects such as ringing, which changes completely when you go to a pcb, no doubt you have a bit of flying lead wiring inductance + capacitance from the bread board that gives the ringing on the edges, certainly put 470nF and 4u7 right across the 555 which will help a little, I assume you are using the modern Cmos version of the 555? To compensate for your wiring L & C (on the bread board) to reduce the ringing you can add a snubber at the receiving end of the signal path, start with 1nF and 220 ohm (in series, placed from o/p to gnd) this should take out the worst of the ringing - you can experiment with values, on a good pcb layout with good de-coupling (caps across the 555 power) you may not need any snubbing - see how you go... good luck..!

Click to expand...

Thanks Orson. I don't think I am using the CMOS verision of the 555. But then again I didn't realize I was using the CMOS chip when I selected a HEF4081 until some one in here pointed out to me that it indeed was.

It is a NE555CN. Is that a CMOS verision? It does not say so in the datasheet, or not that I have noticed.

Orson Cart said:

I assume you are using the modern Cmos version of the 555?

Click to expand...

He is using one ordinary 555 as a high current buffer so I think the oscillator is also an ordinary 555.
The ordinary 555 produces a 400mA shoot-through supply current spike when it switches that I showed.

Re: Ringing in the edges of a Square wave

SunnySkyguy said:

Usually ringing is caused by excessively long scope probe ground inductance and probe capacitance resonating. To fix that remove the ground clip and tip and only use the tip&ring of the barrel on the probe between to adjacent pins for signal and ground.

The other cause is long line driving cable inductance and capacitance not loaded to the characteristic impedance thus ringing or a reactive load. This impedance can be reduced with twisted pair or shielded and terminated with something less than a 500 Ohms, if 50 Ohm cable a series 50R driving the coax and 50R terminating or 120R for twisted pair +/- 30% for 8 turns per foot or used two R's biased to some DC voltage are some options to offers ieal matched impedance and flattest frequency response at the expense of losing half the voltage which got doubled due to a 100% reflection of a high impedance load. ( transmission line theory)

Click to expand...

>boylesg<
To ensure clarity pls answer the following.

1) what is the frequency of the ringing? ( expand to to 1 cycle/div then give sweep us/div f=1/(sweep rate/div))
2) what is the length of ground path from chip to probe including probe clip?
3) what is duration of ringing in # of cycles or duration using straight line asymptote to zero of envelope.
4) does NO adjustment screw mean your probe is x1 ? as I suspected)
5) what is probe cable length? 1m? probe capacitance + scope ( if cant find, my guess is 50pF)
6) did you try my tip&barrel ring measurement method? using two short wires (<1cm) direct on chip (Signal & GND) If NOT, repeat and report results for above.

Audio, at the time my scope was on 10uS, the square wave was roughly 1 division and the ringing was barely wider than the lines on the screen. I am afraid I can't give you an estimate more accurate than that because it has disappeared since I put the decoupling caps in.

My scope cable length is about 1m.

The earth clip is roughly 10cm.

And I had it clipped on the gnd rail on the board a few centimeters from the farthest chip.

There is an adjustment screw, as it turns out) on my probe near the BNC (or what ever you call them) socket but there is no adjustment screw down near the probe, only the x1 / x10 switch (I have it on x10).

did you try my tip&barrel ring measurement method?

Click to expand...

No but then the ringing has gone (or reduced beyond the scopes ability to make it visible) since I put those decoupling caps in.

Have you seen this audio? https://www.edaboard.com/threads/339338/#post1447617
The prospect of being able to create my own custom shape and size copper clad boards is rather exciting.

boylesg said:

Audio, at the time my scope was on 10uS, the square wave was roughly 1 division and the ringing was barely wider than the lines on the screen. I am afraid I can't give you an estimate more accurate than that because it has disappeared since I put the decoupling caps in.

Click to expand...

Then why is everybody else still talking about eliminating the ringing that is fixed??

There is an adjustment screw, as it turns out) on my probe near the BNC (or what ever you call them) socket but there is no adjustment screw down near the probe, only the x1 / x10 switch (I have it on x10).

Click to expand...

The adjustment screw is the trimmer capacitor that is used only on the 10:1 probe attenuation and it is adjusted for a proper looking squarewave when fed a 1kHz to 5kHz squarewave.

Have you seen this audio? https://www.edaboard.com/threads/339338/#post1447617
The prospect of being able to create my own custom shape and size copper clad boards is rather exciting.

Click to expand...

I did not know that you were actually plating copper onto graphite paint on a bare board.
In my electronics career and hobby I made many circuits on stripboard that has parallel strips of copper on a perforated board. The copper strips and a few short along the board jumper wires form half of a pcb and the parts form the other half. Most circuits are small, compact and have parts close together like on a pcb because each copper strip is cut to length with a shallow drill bit that cuts the copper strip between parts but does not drill through the board. Most of my projects were custom with only one circuit made. The stripboard prototype circuit worked perfectly and looked so good that it was sold and installed as the finished product.

Audioguru said:

Then why is everybody else still talking about eliminating the ringing that is fixed??

The adjustment screw is the trimmer capacitor that is used only on the 10:1 probe attenuation and it is adjusted for a proper looking squarewave when fed a 1kHz to 5kHz squarewave.


I did not know that you were actually plating copper onto graphite paint on a bare board.
In my electronics career and hobby I made many circuits on stripboard that has parallel strips of copper on a perforated board. The copper strips and a few short along the board jumper wires form half of a pcb and the parts form the other half. Most circuits are small, compact and have parts close together like on a pcb because each copper strip is cut to length with a shallow drill bit that cuts the copper strip between parts but does not drill through the board. Most of my projects were custom with only one circuit made. The stripboard prototype circuit worked perfectly and looked so good that it was sold and installed as the finished product.

Click to expand...

I duuno why the discussion is still going audio, but I have never the less picked up some more very useful tips along the way so I am not complaining here.

When I get around to it I am going to adjust that screw on my probe as you describe.

As for the copper plating. It has been a bit of an ambition to be able to create a copper clad circuit board. I have experimented a bit with Al tap and various methods of copper plating but have only just found a way that seems to work well.

I am currently painting some MDF with white epoxy paint. I am having to dry it in my oven because it is cold here and the paint otherwise dries painfully slowly. Once the paint is hardened I will give them one coat of west system epoxy resin o make sure they are waterproof. I will give them a light sand to smooth them off and then coat one side in the graphite paint. And then lightly sand that layer.

Once the board is etched (assuming I successfully get that far) I figure the white back ground will ensure I can see that all the exposed graphite paint between the tracks is removed.

An NE555CN is not the CMOS one, it is the old transistor one, as already posted these have a nasty current spike draw at each transition of the o/p, they eventually die from this, some take longer than others.

I conclude from the latest contributions that the thread is solved. It shouldn't be maintained with off-topic discussions like the copper-clad theme.

FvM said:

I conclude from the latest contributions that the thread is solved. It shouldn't be maintained with off-topic discussions like the copper-clad theme.

Click to expand...

Yes mark it as solved.