Square Wave Generator Based on 555 Question.

[PCB.Wiz]

Thank you for the recommendation.  I read the datasheet.
https://assets.nexperia.com/documents/data-sheet/HEF4060B.pdf

Unfortunately the datasheet was not Texas Instruments.  The reason I say that and the reason I like to use Texas Instruments parts is they give a very detailed description of how it operates along with a whole bunch of circuits that I learn from, they also have links to white papers that educate on the subject matter.  Never understood why all companies don't do that.  I will have to do a little bit more research and figure out how to use this chip properly.

Yes, TI data is generally good for new parts, but for their ancient parts like CD4060 and SN74HC4060, they are often scans of old paper printouts.

....  Unfortunately this particular TI datasheet is not the usual kind and doesn't have application notes.  Would you happen to know of a schematic that would work in this particular case that I can analyze and learn from?

The Nexperia data on CMOS logic is probably the best - they have circuits, and equations and curves of typical operation.
(eg their HEF4060 is tagged Rev. 10 — 8 November 2021)

If you are learning, you could try the 15V and 5V CMOS parts and compare them. At your 5kHz and 5V, both will work.

[tggzzz]

Almost entirely the fault of breadboard inductance and lead lengths of scope and power supply leads. Not uncommon for bread boarding and often the reason why bread board projects act weird or fail entirely.

Almost certainly true.

Better breadboard techniques at https://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

[mawyatt]

Agree with CaptDon, following the 555 with a divide by 2 flip-flop (74HC74) gives a very precise 50% duty cycle at lower frequencies regardless of the 555 duty cycle.

Here's a post employing a CMOS divide by 2 concept to produce a precise 50% duty cycle and amplitude waveform for an accurate squarewave reference.

https://www.eevblog.com/forum/testgear/ac-rms-dmm-tests/

Best,

I read your post.  That's pretty neat that you came up with that.  Have there been any changes to the design if I ever decided to make the PCB and build it?   

Like I mentioned before I wasn't striving for 50-50, that's not what this post was about. I was more interested in what's causing that overshoot and if there is a way to correct it.

But I am also glad that people gave me suggestions on the 50-50 duty cycle as it gives me additional information and knowledge.

Thank you.

You can use various parts for this to work, and it does work extremely well as shown!!

We used a CD4060 with a Crystal, Precision 5V reference, and a discrete CMOS Inverting Buffer. You can replace the discrete buffer with a standard CMOS buffer and parallel the outputs for a lower output impedance, any good 5V reference is also OK. Since one can measure the DC value of the 5V reference with a quality DMM, then the AC RMS value can be inferred with very good precision, follow discussion on the indicate thread for more details.

Best,

[JJ_023]

Almost entirely the fault of breadboard inductance and lead lengths of scope and power supply leads. Not uncommon for bread boarding and often the reason why bread board projects act weird or fail entirely.

Almost certainly true.

Better breadboard techniques at https://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

Thanks for the link.  It was an interesting read.  I have worked with Perf board.  But according to that article it's a lot less desirable than some of the other techniques.  I seen the other techniques utilized by others.  I have always sided away from them due to the convoluted mess they create.  But since so many well-regarded engineers use them I will have to reconsider and give it a try.

[tggzzz]

Almost entirely the fault of breadboard inductance and lead lengths of scope and power supply leads. Not uncommon for bread boarding and often the reason why bread board projects act weird or fail entirely.

Almost certainly true.

Better breadboard techniques at https://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

Thanks for the link.  It was an interesting read.  I have worked with Perf board.  But according to that article it's a lot less desirable than some of the other techniques.  I seen the other techniques utilized by others.  I have always sided away from them due to the convoluted mess they create.  But since so many well-regarded engineers use them I will have to reconsider and give it a try.

Glad you liked it.

I've seen too many beginners be disheartened by the subtle (and not so subtle) problems getting their designs working with solderless breadboards. Perfboards have fewer problems. All techniques (including PCBs) have some disadvantages.

The key points are to understand the positive and negative characteristics or every technique, weigh those against what you are doing, and choose the appropriate combination of techniques for that specific job.

[RoGeorge]

What is causing this overshoot and what could be done to correct it.

Before anything, have you calibrated the oscilloscope probes recently?

If not, note that there is a small trimmer inside of the probe's handle.  Set the probe switch on 10x, attach it to the calibration signal from the oscilloscope, and turn the small trimmer to get the most flat response, with minimal overshoots/undershoots.  The procedure is usually described with pictures in the oscilloscope's user manual, or in the probe's user manual.

To get 50% precisely, as already said before, the easiest way is to start from 10kHz and divide it by 2 with a flip-flop (FF), to make it 5kHz .  That will get you a 50% duty factor with no adjustement needed.  Otherwise, the adjustement for 50% can be tedious to achieve, and hard to maintain it over time, or over temperature/Vcc/etc. variations.

Kind request, please avoid starting titles or conversations with the word "so".  My first language is not English, but in general, the word "so" as a start is not a good sign. 

[JJ_023]

Almost entirely the fault of breadboard inductance and lead lengths of scope and power supply leads. Not uncommon for bread boarding and often the reason why bread board projects act weird or fail entirely.

Almost certainly true.

Better breadboard techniques at https://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

Thanks for the link.  It was an interesting read.  I have worked with Perf board.  But according to that article it's a lot less desirable than some of the other techniques.  I seen the other techniques utilized by others.  I have always sided away from them due to the convoluted mess they create.  But since so many well-regarded engineers use them I will have to reconsider and give it a try.

Glad you liked it.

I've seen too many beginners be disheartened by the subtle (and not so subtle) problems getting their designs working with solderless breadboards. Perfboards have fewer problems. All techniques (including PCBs) have some disadvantages.

The key points are to understand the positive and negative characteristics or every technique, weigh those against what you are doing, and choose the appropriate combination of techniques for that specific job.

I did enjoy it thank you.  Do you have any specific tips for using a perf board?  I try to keep everything close together and use solid wire to make the necessary connections.  If I can which is often not the case I try not to cross any wires.

[JJ_023]

What is causing this overshoot and what could be done to correct it.

Before anything, have you calibrated the oscilloscope probes recently?

If not, note that there is a small trimmer inside of the probe's handle.  Set the probe switch on 10x, attach it to the calibration signal from the oscilloscope, and turn the small trimmer to get the most flat response, with minimal overshoots/undershoots.  The procedure is usually described with pictures in the oscilloscope's user manual, or in the probe's user manual.

To get 50% precisely, as already said before, the easiest way is to start from 10kHz and divide it by 2 with a flip-flop (FF), to make it 5kHz .  That will get you a 50% duty factor with no adjustement needed.  Otherwise, the adjustement for 50% can be tedious to achieve, and hard to maintain it over time, or over temperature/Vcc/etc. variations.

Kind request, please avoid starting titles or conversations with the word "so".  My first language is not English, but in general, the word "so" as a start is not a good sign. 

Thank you for the suggestion.  Whenever I use any piece of test equipment I always do a very basic test.  Since I primarily always operate on 10X, every time I turn on the scope I quickly hook up to the scopes reference to check.  I learned this a long long time ago.  It's a lot quicker to troubleshoot a piece of equipment that you use for troubleshooting before you start using it. 

[2N3055]

Are you using scope probe with ground wire and crocodile clip, or you use spring ground right at the tip?

[JJ_023]

Are you using scope probe with ground wire and crocodile clip, or you use spring ground right at the tip?

That's a good point.  I was using a 3 inch alligator Crocodile clip.

[2N3055]

Are you using scope probe with ground wire and crocodile clip, or you use spring ground right at the tip?

That's a good point.  I was using a 3 inch alligator Crocodile clip.

That alone can create that overshoot.
Try with spring ground, or if you don't have one wind thicker copper wire around it and solder to ground.

[tggzzz]

I did enjoy it thank you.  Do you have any specific tips for using a perf board?  I try to keep everything close together and use solid wire to make the necessary connections.  If I can which is often not the case I try not to cross any wires.

Nothing beyond that.

I find Manhattan (in any of the variants shown) easier because there is less planning (=>faster) plus a solid groundplane (=> electrically better), and a sheet of copper clad can be large and is cheap and strong.

Have fun!

[eneuro]

Almost entirely the fault of breadboard inductance and lead lengths of scope and power supply leads.

There is no point in analyzing projects run on a breadboard 

[JJ_023]

If you're after 50/50 square wave, you might have better luck with this alternative 555 astable configuration, rather than the standard astable configuration.

(Attachment Link)

I went to play with this particular circuit and just realized it doesn't have a discharge pin connection.  How does this work?

[JJ_023]

Are you using scope probe with ground wire and crocodile clip, or you use spring ground right at the tip?

That's a good point.  I was using a 3 inch alligator Crocodile clip.

That alone can create that overshoot.
Try with spring ground, or if you don't have one wind thicker copper wire around it and solder to ground.

This is why I responded the way that I did.  I should know better but just overlooked it.  I actually have several of those spring grounds.  Thank you.

[PCB.Wiz]

I went to play with this particular circuit and just realized it doesn't have a discharge pin connection.  How does this work?

it does not need one, the 555 behaves as an inverting Schmitt buffer. it does not quite manage rail-rail, so the added pullup allows you to skew to 50%

[JJ_023]

I went to play with this particular circuit and just realized it doesn't have a discharge pin connection.  How does this work?

it does not need one, the 555 behaves as an inverting Schmitt buffer. it does not quite manage rail-rail, so the added pullup allows you to skew to 50%

I'm going to try that circuit thank you for the explanation. 

I continued playing with this circuit to try and see what would help with the oscillation.  I tried all the suggestions from the posts.  Changing over to a spring ground clip did not really do much in this particular case ( although I know it is a valid suggestion).  What made the most difference was putting a 100 nF ceramic capacitor on Vcc to ground. 

My question is now that the oscillation is mostly removed are we approaching the limits of this particular chip in terms of how crisp of a leading edge we can get just based on the chip itself?

Just as a data point the circuit was slightly different that's why the voltage ,frequency and duty cycle do not match the original post.  I wanted to see if I could re-create the Oscillations using different parameters. 

[JJ_023]

I made the other version that was  suggested for the A-stable 555.  The image is attached.  It managed a 50% duty cycle.  Thank you guys for the suggestion. 

I noticed that the output is not as clean and sharp even with a capacitor at Vcc.  See the attached image. 

[Andy Chee]

If you're after 50/50 square wave, you might have better luck with this alternative 555 astable configuration, rather than the standard astable configuration.

(Attachment Link)

I went to play with this particular circuit and just realized it doesn't have a discharge pin connection.  How does this work?

When the 555 is triggered to discharge, normally it is pin 7 which turns on an internal open collector transistor and shorts the capacitor to ground.  In the above alternative configuration, we use the totem output on pin 3 to short the capacitor to ground.

However the feature of interest is the charging path, rather than the discharge path.  In the standard astable configuration, the charging path is via a different resistor.  In the above alternative configuration, the charging path is via the totem output high on pin 3 and the SAME resistor.

Having the charge and discharge path via the SAME resistor is what makes it easier to get 50/50, because you no longer have to precisely make the the two resistors equal.

Come to think of it, try omitting R1 100kohm resistor.  I don't think it's required provided you're using the CMOS 7555 variant.  And even if you have the regular TTL 555, try removing it anyway and see what it does to the output duty cycle.

The output may certainly have more overshoot on the leading edges, this is to be expected due to the high current totem output doing the capacitor charging.

[RoGeorge]

every time I turn on the scope I quickly hook up to the scopes reference to check

To be honest, I never do that.  I touch the tip of the probe with the finger. 

About probe calibration.  It doesn't need to be adjusted very often, unless really big variations in temperature or air humidity happened since last calibration.  About temperature, any calibration has to be done after about half an hour or so of idle running, so the instrument got to a stable temperature/humidity regime.  If you calibrate the probe right at startup, after an hour of running, the calibration might be off, particularly if you are in an are with high air humidity and potential condensation.

Another thing, when calibrating, you have to connect both the tip and the Ground of the probe.

In the pic you attached at the OP, there are 2 things:
- a very short spike right after each signal edge - that is from the inductance of the GND alligator wire.  In fact, by how tall that spike is, I suspect you are probing with only one wire (as in, another probe was used only to connect its GND alligator to the minus, then the displayed line in the picture is from a second probe with its alligator disconnected)
- then, a long but small amplitude slope, for about half the width where the line was supposed to be flat - that might be from the probe calibration.  Not a certitude, but might be.

To eliminate the calibration hypothesis, please post a printscreen of the calibration signal, then a printscreen of the 555 signal.  Both taken at about the same time, one after another, and what's most important, both taken by making use of the GND alligator, don't let it disconnected.

A 3rd capture while using the spring connector at the tip of the probe, and by touching the GND and the out pins of the 555 directly with the spring attachment that came with the probes.  Then a 4'th pic with the physical circuit on the breadboard, with the measuring probe(s) connected.

I'm asking for all 4 pictures because I know you are careful to details, and particularly interested in getting the optimal.  We can discuss the 4 pics later as a concrete example, in order to highlight more details about electronics in general, and probing in particular.

[JJ_023]

If you're after 50/50 square wave, you might have better luck with this alternative 555 astable configuration, rather than the standard astable configuration.

(Attachment Link)

I went to play with this particular circuit and just realized it doesn't have a discharge pin connection.  How does this work?

When the 555 is triggered to discharge, normally it is pin 7 which turns on an internal open collector transistor and shorts the capacitor to ground.  In the above alternative configuration, we use the totem output on pin 3 to short the capacitor to ground.

However the feature of interest is the charging path, rather than the discharge path.  In the standard astable configuration, the charging path is via a different resistor.  In the above alternative configuration, the charging path is via the totem output high on pin 3 and the SAME resistor.

Having the charge and discharge path via the SAME resistor is what makes it easier to get 50/50, because you no longer have to precisely make the the two resistors equal.

Come to think of it, try omitting R1 100kohm resistor.  I don't think it's required provided you're using the CMOS 7555 variant.  And even if you have the regular TTL 555, try removing it anyway and see what it does to the output duty cycle.

The output may certainly have more overshoot on the leading edges, this is to be expected due to the high current totem output doing the capacitor charging.

I appreciate the detailed explanation.  It all makes sense.  I tried your suggestion.  You can see the results in the attached. 

My 1st question is why did you recommend 100 K ohm resistor in the 1st place if this works without it?

The setup Is attached with the  100 K ohm resistor omitted.  I tried different variations of R2.  The images attached show the values for R2.

The capacitors were 47nF.

Here are the following observations

I was not able to achieve a 50% duty cycle with one resistor.

The waveform does not seem as stable as the original.

The 555 that I am using is the Texas Instruments SE555.  https://www.ti.com/lit/ds/symlink/se555.pdf?ts=1704543624724

I had a few of these around and I like this particular chip because unlike most  555 chips it will operate up to 18V.  I don't think this is a CMOS variant maybe someone can correct me or affirm me.

Again thank you.

[JJ_023]

every time I turn on the scope I quickly hook up to the scopes reference to check

To be hones, I never do that.  I touch the tip of the probe with the finger. 

About probe calibration.  It doesn't need to be adjusted very often, unless really big variations in temperature or air humidity happened since last calibration.  About temperature, any calibration has to be done after about half an hour or so of idle running, so the instrument got to a stable temperature/humidity regime.  If you calibrate the probe right at startup, after an hour of running, the calibration might be off, particularly if you are in an are with high air humidity and potential condensation.

Another thing, when calibrating, you have to connect both the tip and the Ground of the probe.

In the pic you attached at the OP, there are 2 things:
- a very short spike right after each signal edge - that is from the inductance of the GND alligator wire.  In fact, by how tall that spike is, I suspect you are probing with only one wire (as in, another probe was used only to connect its GND alligator to the minus, then the displayed line in the picture is from a second probe with its alligator disconnected)
- then, a long but small amplitude slope, for about half the width where the line was supposed to be flat - that might be from the probe calibration.  Not a certitude, but might be.

To eliminate the calibration hypothesis, please post a printscreen of the calibration signal, then a printscreen of the 555 signal.  Both taken at about the same time, one after another, and what's most important, both taken by making use of the GND alligator, don't let it disconnected.

A 3rd capture while using the spring connector at the tip of the probe, and by touching the GND and the out pins of the 555 directly with the spring attachment that came with the probes.  Then a 4'th pic with the physical circuit on the breadboard, with the measuring probe(s) connected.

I'm asking for all 4 pictures because I know you are careful to details, and particularly interested in getting the optimal.  We can discuss the 4 pics later as a concrete example, in order to highlight more details about electronics in general, and probing in particular.

Thank you again for such a detailed response.

You probably shouldn't touch the tip.

I am familiar with the calibration process fairly well.

You say the spike is at the end of the waveform I thought that was the beginning of the waveform.  Which 1 of us is correct?

Here are a few data points.  The ground clip was always used.  It was used alligator style from the probe that took the measurement. You can see the probe placement in the original breadboard set up in 1 of the attached pictures below.

As you requested.  The 1st picture and the 2nd picture are both of the probe calibration signal.  The 3rd picture is the schematic that was utilized.  The 4th picture is the original setup that was used.  The 5th picture is the set up that was in response to this post.

The 6th picture is utilizing the alligator clip.  The goldplated pins on the breadboard is where the connection was made.

The 7th picture is utilizing a spring ground.  The connection was made directly from pin 1 to pin 3 by the probe.

Looking forward to your comments as well as anybody else that wants to chime in.  Tips and criticism welcomed.

[Andy Chee]

My 1st question is why did you recommend 100 K ohm resistor in the 1st place if this works without it?

Well when I first posted the circuit, I had no idea which 555 you were using!

Your SE555 is indeed the TTL version, so using the 100k will help make the duty cycle closer to 50/50. 

If using the CMOS 7555 version, this resistor can be omitted because its pin 3 output will have a more balanced voltage swing compared to the TTL.

[JJ_023]

My 1st question is why did you recommend 100 K ohm resistor in the 1st place if this works without it?

Well when I first posted the circuit, I had no idea which 555 you were using!

Your SE555 is indeed the TTL version, so using the 100k will help make the duty cycle closer to 50/50. 

If using the CMOS 7555 version, this resistor can be omitted because its pin 3 output will have a more balanced voltage swing compared to the TTL.

Thanks for the response.  I did a little bit more reading on the 7555.  I found an interesting version which goes up to 2.5 megahertz.  In their datasheet it talks about exactly that, being able to run a stable mode with one resistor.

http://www.aldinc.com/pdf/ALD7555-7556.pdf

[Andy Chee]

And for a bit of a twist in 555 variants, here's one built with a (non-volatile) programable decade counter:

https://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555_Spec_2.pdf

(see page 2 for a block diagram)

Coming from a 12C509 programming history, after all these years I'm still not exactly sure which niche the CSS555 fulfils.