Author Topic: Portable Low Frequency square wave generator circuit - Solved - page 3  (Read 14168 times)

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Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #25 on: January 31, 2019, 03:46:55 pm »
I would appreciate a little more politeness and less rudeness. I make a habit of trying to ignore rudeness because I prefer not to escalate.

I have been working with 555 timers since before most people on this forum were born.  In 1977 I was already using 555 timers and bought The IC Timer Cookbook (pdf) which I still have on my shelf.  Around 1980 I was running a small home business with a friend building and selling timers for photography enlargers. A lot of people were developing their own photos at home and needed a timer for the enlarger. We sold maybe a thousand or two. I still have the circuit and PCB. Two scales: up to 60 seconds and up to 3 minutes.

The LM555 (pdf) is bipolar and the mother of all later CMOS.
« Last Edit: January 31, 2019, 03:59:51 pm by soldar »
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #26 on: January 31, 2019, 04:24:54 pm »
The original poster wanted 12V peak to peak, not 24V, but that's an easy mistake to make, since it wasn't clear and it's trivial to reduce the supply voltage to +/-6V.
No mistake. The output impedance is 50R forward terminated and the output voltage is +-6V8, as the OP informed me that he wants a little over 6V. The output voltage can be adjusted to any voltage from 2V to 12V by changing the two zener diodes at the output.
The original poster didn't actually say 12V peak to peak into a 50 Ohm load. They said 12V peak to peak with an output impedance of 50 Ohm. It's understandable you interpreted it as 12Vpp into a 50Ohm load, with an output impedance of 50Ohm. Indeed you could be right, as the original poster wasn't very clear.

What on earth is all this mark to space ratio stuff all about? The circuit as presented will meet the OPs requirement and that is it.
There is no more to say.  By the way the 555 is a CMOS type.
Except the mark space ratio will not be 50% at 1kHz, because the value of R1 is so low the on resistances of the 7555's internal MOSFETs will skew the duty cycle considerably. The output stage inside the 7555 is not perfect. The output transistors have asymmetrical on resistances. The high side transistor's resistance is between 1k and 150R and low side transistor's resistance between 143Ohm and 16Ohm, depending on the supply voltage to the 7555. The higher the supply voltage, the lower the on resistances.

I worked out the resistances, using the figures given on the graphs on pages 6 and 7 of the datasheet.
https://www.nxp.com/docs/en/data-sheet/ICM7555.pdf

The on resistances with a supply voltage of 12V are not specified. Suppose high side is 200R and low side 30R. The capacitor will be changing via R1+200R = 1k2, which will take longer than discharging via 30R+R1 = 1k03, so the duty cycle won't be 50%.

I understand you felt personally attacked when I made this assertion but it was not my intention. It is something which is easily overlooked. Please build a 7555 oscillator, with 50% duty cycle configuration and a 1k timing resistor and you'll see what I mean. Note how the duty cycle is nearer to 50%, when the power supply voltage is 18V, than it is at 2V, because the on resistances of the output transistors are lower and contribute less to the timing.

A much higher value for R1, say 10k, could be selected to make the duty cycle much nearer to 50% and use a much smaller capacitor, but then the potentiometer would need to be 20M, to get down to 1Hz and the current so low it would be prone to noise, hence why I suggested different ranges.
 

Online iMo

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Re: Portable Low Frequency square wave generator circuit
« Reply #27 on: January 31, 2019, 04:43:50 pm »
This is probably the simplest wiring which could work.
It gives you aprox +/-6V at the output, you may set the frequency and 50% duty by the 2 pots.
You need a switch for frequency range selection.
You may play with the values, I think 50k lin pot in freq and duty is ok, the values selection for the capacitors - the calculation is left to the readers..
You need the NE555 (not the CMOS) when required 50ohm output.
C1-C4 should be foil capacitors (for highest stability use quality one, ie. WIMA for 63V).
The C7 is an elyt 100uF/25V.
No warranties of any kind, use at your own risk :)
« Last Edit: January 31, 2019, 05:51:30 pm by imo »
Readers discretion is advised..
 
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Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #28 on: January 31, 2019, 06:32:37 pm »
Zero999, the OP is kind of confusing and contradictory even but I get the idea that this is to simulate some speed signal sent by some transducer on a train and I feel quite safe assuming there is quite some latitude in voltage, duty cycle, etc.

imo, that looks good.
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Online iMo

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Re: Portable Low Frequency square wave generator circuit
« Reply #29 on: January 31, 2019, 06:50:05 pm »
I do not know how is it with trains in UK, but the trains in EU are mostly fully controlled by computers. Last summer we were standing in the middle of nowhere for 3 hours because a faulty "door sensor" in one of carriages sent an "open door" signal. And the loco driver did anything with that as the computer said "no-go". So I can hardly imagine you can fool an locomotive such easily :)
Readers discretion is advised..
 
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Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #30 on: January 31, 2019, 07:00:58 pm »
imo, if you read the OP you will read that is exactly what he is trying to do.
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #31 on: February 01, 2019, 11:13:34 am »
One thing that surprises me is that no one has commented on the circuits effect on global warming. After all there is a whole 1W2 being dissipated in the output stage.:-DD
Good point. It's being powered from a small battery, so 1.2W of idle power consumption is a killer.

As I have said before to all you armchair 'experts': Let us see your complete circuit, embodying all these wonderful ideas that you have.
We tend to avoid posting complete circuits here, as it discourages people from thinking. It's often more helpful to post hints and little circuits which the original poster can put together, that way they gain a deeper understanding of how it works, rather than some soldering practice.
What on earth is all this mark to space ratio stuff all about?
What on earth is all this dual supply rail stuff about?  ;) Only one power supply is needed. The trick is to float it. I did hint on this earlier, but I forgot this is the beginners section so should have posted a schematic.

50% duty cycle is achieved by replacing the usual pull-up resistor on the discharge pin with a transistor driven from another 555 (Q1) which inverts the signal, so it's pulled all the way up to +V when charging. If a bridged output isn't needed, the other 555 could be replaced with an NPN BJT, with its base connected to the 555's output via a suitable current limiting resistor. Of course in real life, a NE556 dual timer could be used to save space.

One thing to note is the simulation says it outputs +/-9V, but this doesn't represent reality, since the model doesn't mimic the NE555's output stage very accurately. The output voltage will be a little less, much closer to 6V, especially when loaded. It may be necessary to power the circuit from two 9V batteries and a regulator, as the battery voltage will fall, as it discharges. Heck, I'd consider swapping the 9V battery for some AA cells, which have a higher energy density.
« Last Edit: February 01, 2019, 11:24:57 am by Zero999 »
 

Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #32 on: February 01, 2019, 11:48:09 am »
We tend to avoid posting complete circuits here, as it discourages people from thinking. It's often more helpful to post hints and little circuits which the original poster can put together, that way they gain a deeper understanding of how it works, rather than some soldering practice.


Let me expand on this. This is not a free service where people work for you for free and provide you with turnkey solutions.  We are here to help and learn from each other.  If you want a turnkey solution you can go hire some engineer and pay them the going rate.

Furthermore, many requests are poorly defined, poorly presented and poorly explained or even contradictory. Often getting further clarification from the OP is a slow and painful process, somewhat like pulling teeth.

We could be here presenting solutions for days only to have the OP disappear (often happens) or reject different solutions on different grounds (to complicated, too expensive, not fulfilling needs which were not mentioned before, etc).

So we take what we are given and kick ideas around and learn from others' ideas and viewpoints. That is the way I see it.
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #33 on: February 01, 2019, 01:03:10 pm »
I think the OP has gone, but who cares? This is interesting.

Has anyone actually tried building the 50% duty cycle 7555 circuit before?

I thought I'd breadboard it. I aimed for 1.53kHz, and tried the following values for R and C: 1k & 470nF, 10k & 47nF and 100k & 4.7nF. Firstly I tried using a 5V supply, which I increased to 15V.

The results were interesting. Even the 100k and 4.7nF combination didn't give exactly 50% duty cycle.

Schematic.


R = 1k, C = 470nF, V = 5V
56.3% duty

R = 1k, C = 470nF, V = 15V
51.7% duty

R = 10k, C = 47nF, V = 15V
48.4% duty

R = 100k, C = 4.7nF, V = 15V
48.2% duty


Conclusion: if the duty cycle is critical, then don't use the 7555!
« Last Edit: February 01, 2019, 01:11:41 pm by Zero999 »
 

Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #34 on: February 01, 2019, 01:28:41 pm »
I thought that wasn't very good, so I tried a different brand IC which gave better results. The ICs used in my previous test were Philips brand. The ones I used for this test were Intersil. Due to time constraints, I didn't bother repeating all of the tests, just the 1k & 470nF and 100k & 4.7nF with a supply voltage of 15V.

R = 1k, C = 470nF
53.3% duty


R = 100k, C = 4.7nF
49.7% duty
« Last Edit: February 01, 2019, 01:32:41 pm by Zero999 »
 

Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #35 on: February 01, 2019, 01:51:30 pm »
I remember building decades ago a pulse generator which could go from (say) 1% to 99% duty cycle and voltage from something like 5 V to about 15 V. It was for lab testing some devices and it was simply a 555 with a variable voltage supply and the supply was little more than a pot voltage divider with an emitter follower transistor. Put it all in a nice box and it felt like it was something. I was working for Kodak at the time and my co-workers looked up to me like I was a genius.

But, yes, the 555 timer is not a precision thing. Changing one thing , like supply voltage, will affect the others. It is good for simple, quick and dirty solutions.
 
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #36 on: February 01, 2019, 11:11:36 pm »
I wonder if the first 7555 was faulty, or is that kind of error normal? I just don't have the time or motivation to test a whole load of ICs.
 

Offline nsrmagazin

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Re: Portable Low Frequency square wave generator circuit
« Reply #37 on: February 06, 2019, 03:02:13 pm »
Here is the power supply:
http://powersupply33.com/simple-split-rail-power-supply-lm380.html/split-power-supply
For "Vin" you have 2x"9VDC" batteries in series.

Here is the circuit itself for what you need.
http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/square.html
Making the resistor a pot gives you varying frequency.

The tolerance will depend on the components used. Recommended are "1%" tolerance resistors.
Hi all!
If you like the post, please press "thanks".
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #38 on: February 06, 2019, 03:59:32 pm »
I would appreciate a little more politeness and less rudeness. I make a habit of trying to ignore rudeness because I prefer not to escalate.
In that case, you should practice what you preach. And you did escalate.
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #39 on: February 06, 2019, 04:06:55 pm »

I have been working with 555 timers since before most people on this forum were born.  In 1977 I was already using 555 timers and bought The IC Timer Cookbook (pdf) which I still have on my shelf.  Around 1980 I was running a small home business with a friend building and selling timers for photography enlargers. A lot of people were developing their own photos at home and needed a timer for the enlarger. We sold maybe a thousand or two. I still have the circuit and PCB. Two scales: up to 60 seconds and up to 3 minutes.

The LM555 (pdf) is bipolar and the mother of all later CMOS
It doesn't matter what you have done or what you are. That does not grant you the right to make derogatory unfounded statements about other peoples designs.

Just for the record, I have been designing circuits since before the 555 was even thought of. In fact I had a 555 chip before they were released in the UK.
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #40 on: February 06, 2019, 04:12:45 pm »
The OP requested a circuit and out of all the posts on this thread, there is only one circuit has been posted- guess which one.

My question is whether anyone on this forum knows about a working circuit which I could utilize to build my little project.
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #41 on: February 06, 2019, 04:26:51 pm »
What on earth is all this mark to space ratio stuff all about? The circuit as presented will meet the OPs requirement and that is it.
There is no more to say.  By the way the 555 is a CMOS type.
Except the mark space ratio will not be 50% at 1kHz, because the value of R1 is so low the on resistances of the 7555's internal MOSFETs will skew the duty cycle considerably. The output stage inside the 7555 is not perfect. The output transistors have asymmetrical on resistances. The high side transistor's resistance is between 1k and 150R and low side transistor's resistance between 143Ohm and 16Ohm, depending on the supply voltage to the 7555. The higher the supply voltage, the lower the on resistances.

I worked out the resistances, using the figures given on the graphs on pages 6 and 7 of the datasheet.
https://www.nxp.com/docs/en/data-sheet/ICM7555.pdf

Your missing some very important points.

  • The OP does not want an exact 1:1 mak-to space ratio so what figure are you using to justify your negative comments about the MS ratio?
  • You have made general and sweeping statements about the MS ratio with a few figures quoted but no complete calculations for the M/S ration
  • You have not taken into accout the end resistance of the 2M potentiometer which adds to the effective resistance seen by the C555
  • And worst of all you have failed to realise that the 1k resistor is a stopper so that the lowest resistance possibly seen by the C555 output  is defined. If you do the calculations you will find that oscillator reaches 1KHz (the highest frequency requirement) well before 1kHz is reached.
« Last Edit: February 06, 2019, 04:50:41 pm by spec »
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #42 on: February 06, 2019, 04:30:55 pm »
We tend to avoid posting complete circuits here, as it discourages people from thinking. It's often more helpful to post hints and little circuits which the original poster can put together, that way they gain a deeper understanding of how it works, rather than some soldering practice.


Let me expand on this. This is not a free service where people work for you for free and provide you with turnkey solutions.  We are here to help and learn from each other.  If you want a turnkey solution you can go hire some engineer and pay them the going rate.

Furthermore, many requests are poorly defined, poorly presented and poorly explained or even contradictory. Often getting further clarification from the OP is a slow and painful process, somewhat like pulling teeth.

We could be here presenting solutions for days only to have the OP disappear (often happens) or reject different solutions on different grounds (to complicated, too expensive, not fulfilling needs which were not mentioned before, etc).

So we take what we are given and kick ideas around and learn from others' ideas and viewpoints. That is the way I see it.
  :wtf:
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #43 on: February 06, 2019, 04:36:51 pm »
One thing that surprises me is that no one has commented on the circuits effect on global warming. After all there is a whole 1W2 being dissipated in the output stage.:-DD
Good point. It's being powered from a small battery, so 1.2W of idle power consumption is a killer.
Your making this up. The OP said it could be mains powered.

Besides which, 2W2 is no big deal, even for battery power.





 

Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #44 on: February 06, 2019, 04:39:49 pm »
It doesn't matter what you have done or what you are. That does not grant you the right to make derogatory unfounded statements about other peoples designs.

Just for the record, I have been designing circuits since before the 555 was even thought of. In fact I had a 555 chip before they were released in the UK.
I have no idea what your problem is with me since all my posts in this thread have been cordial exchanges with Zero999 and I have not once in this thread addressed or responded to your posts or made any comment about them. I do not understand your attitude and I have no idea why you called me "presumptuous". I don't know if you are mistaking me with someone else from some other thread or what. I have made no comments on anything you have said in this thread or, as far as I can remember, in any other thread.

I have reported your posts in the hope that you will just leave me alone. 

E.T.A: I see you also have a beef with Zero999. Are you sure it's us? Maybe you are just misinterpreting people's motives? Why the confrontational attitude?
« Last Edit: February 06, 2019, 04:47:59 pm by soldar »
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Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #45 on: February 06, 2019, 04:44:34 pm »
Has anyone actually tried building the 50% duty cycle 7555 circuit before?
You keep raising a flag and saluting it. There is no requirement for an exact 1:1 M/S ratio. If it were required I would have done it- it's dead simple to do.

Then, of course you would be able to bang on about a 1:1 M/S ratio not being required and the circuit is too complicated.
« Last Edit: February 06, 2019, 05:11:50 pm by spec »
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #46 on: February 06, 2019, 05:10:52 pm »
It doesn't matter what you have done or what you are. That does not grant you the right to make derogatory unfounded statements about other peoples designs.

Just for the record, I have been designing circuits since before the 555 was even thought of. In fact I had a 555 chip before they were released in the UK.
I have no idea what your problem is with me since all my posts in this thread have been cordial exchanges with Zero999 and I have not once in this thread addressed or responded to your posts or made any comment about them. I do not understand your attitude and I have no idea why you called me "presumptuous". I don't know if you are mistaking me with someone else from some other thread or what. I have made no comments on anything you have said in this thread or, as far as I can remember, in any other thread.

I have reported your posts in the hope that you will just leave me alone. 

E.T.A: I see you also have a beef with Zero999. Are you sure it's us? Maybe you are just misinterpreting people's motives? Why the confrontational attitude?
Just read my posts and reply to them specifically and directly. That is the way that things are resolved.

I have no beef with anyone- just what they do or say. I just posted a schematic and you and zero99 have been making unwarranted negative comments about it, continuously, implying it is not up to the job.  I didn't want to waste time replying to all the comments, but have been forced to do so.

And the final killer is that you and zero99 are now implying that there is something wrong with posting a schematic to meet the OP's requirement. By the way, if I hadn't posted the schematic, this thread would have died, as many others have.

I would welcome a constructive discussion about any schematic that I post, especially about an error. But the whole tone has been dictatorial and negative ... and in error.

I would appreciate it if you could stick to facts, as posted, and not go in for gratuitous personal innuendo.
« Last Edit: February 06, 2019, 06:05:45 pm by spec »
 

Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #47 on: February 06, 2019, 05:40:13 pm »
Has anyone actually tried building the 50% duty cycle 7555 circuit before?
You keep raising a flag and saluting it. There is no requirement for an exact 1:1 M/S ratio. If it were required I would have done it- it's dead simple to do.

Then, of course you would be able to bang on about a 1:1 M/S ratio not being required and the circuit is too complicated.
If it's that simple then why not do it? The CD4013 circuit I posted previously would do that. It doesn't take much imagination to connect it to a suitable MOSFET driver to give the required +/-6V out.

It doesn't matter what you have done or what you are. That does not grant you the right to make derogatory unfounded statements about other peoples designs.

Just for the record, I have been designing circuits since before the 555 was even thought of. In fact I had a 555 chip before they were released in the UK.
I have no idea what your problem is with me since all my posts in this thread have been cordial exchanges with Zero999 and I have not once in this thread addressed or responded to your posts or made any comment about them. I do not understand your attitude and I have no idea why you called me "presumptuous". I don't know if you are mistaking me with someone else from some other thread or what. I have made no comments on anything you have said in this thread or, as far as I can remember, in any other thread.

I have reported your posts in the hope that you will just leave me alone. 

E.T.A: I see you also have a beef with Zero999. Are you sure it's us? Maybe you are just misinterpreting people's motives? Why the confrontational attitude?
I have no beef with anyone- just what they do or say. I just posted a schematic and you and zero99 have been making unwarranted negative comments about it, implying it is not up to the job.  I didn't want to waste time replying to all the comments, but have been forced to do so.

And the final killer is that you and zero99 are now implying that there is something wrong with posting a schematic to meet the OP's requirement. By the way, if I hadn't posted the circuit, this thread would have died, as many others have.

I would welcome a discussion about any schematic that I post, especially about an error. But the whole tone has been dictatorial and negative ... and in error.
  • No, we just pointed out that it has room for improvement. Part of the problem is the original poster's requirements were ambiguous. He said he wanted something portable and preferably battery powered.
  • No one forced you to do anything.
  • No we didn't, by all means please do post schematics. I'm certainly glad you posted the schematic because it prompted me to breadboard the 7555 astable to see how well it meets the 50% duty cycle criteria.
  • No, you're clearly not interested in what anyone has to say about the circuits you post. The tone of this thread was cordial, until you started getting defensive in response to some polite feedback on the circuit you posted.
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #48 on: February 06, 2019, 05:49:25 pm »
Has anyone actually tried building the 50% duty cycle 7555 circuit before?
You keep raising a flag and saluting it. There is no requirement for an exact 1:1 M/S ratio. If it were required I would have done it- it's dead simple to do.

Then, of course you would be able to bang on about a 1:1 M/S ratio not being required and the circuit is too complicated.
If it's that simple then why not do it? The CD4013 circuit I posted previously would do that. It doesn't take much imagination to connect it to a suitable MOSFET driver to give the required +/-6V out.

It doesn't matter what you have done or what you are. That does not grant you the right to make derogatory unfounded statements about other peoples designs.

Just for the record, I have been designing circuits since before the 555 was even thought of. In fact I had a 555 chip before they were released in the UK.
I have no idea what your problem is with me since all my posts in this thread have been cordial exchanges with Zero999 and I have not once in this thread addressed or responded to your posts or made any comment about them. I do not understand your attitude and I have no idea why you called me "presumptuous". I don't know if you are mistaking me with someone else from some other thread or what. I have made no comments on anything you have said in this thread or, as far as I can remember, in any other thread.

I have reported your posts in the hope that you will just leave me alone. 

E.T.A: I see you also have a beef with Zero999. Are you sure it's us? Maybe you are just misinterpreting people's motives? Why the confrontational attitude?
I have no beef with anyone- just what they do or say. I just posted a schematic and you and zero99 have been making unwarranted negative comments about it, implying it is not up to the job.  I didn't want to waste time replying to all the comments, but have been forced to do so.

And the final killer is that you and zero99 are now implying that there is something wrong with posting a schematic to meet the OP's requirement. By the way, if I hadn't posted the circuit, this thread would have died, as many others have.

I would welcome a discussion about any schematic that I post, especially about an error. But the whole tone has been dictatorial and negative ... and in error.
  • No, we just pointed out that it has room for improvement. Part of the problem is the original poster's requirements were ambiguous. He said he wanted something portable and preferably battery powered.
  • No one forced you to do anything.
  • No we didn't, by all means please do post schematics. I'm certainly glad you posted the schematic because it prompted me to breadboard the 7555 astable to see how well it meets the 50% duty cycle criteria.
  • No, you're clearly not interested in what anyone has to say about the circuits you post. The tone of this thread was cordial, until you started getting defensive in response to some polite feedback on the circuit you posted.
Here we go again... on and on- you just never let go do you. I asked you a while back to get off my back- can you please do so.
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #49 on: February 06, 2019, 05:54:48 pm »
Just for the record I tried to avoid all the negative statements about the circuit, but it got so intense and extended that I had to counter it.  I don't care, but the problem is that others, who don't know about design, who read this thread will think that the comments you have been making are relevant and that the circuit is no good. This has happened quite a few times on other threads.

Another thing to remember is it is not your prerogative to tell members how to design or demand that they do this or that. As far as I know you are just a member, like everyone else. For example, if I want to use split supplies- and I have good reason for doing so- I will. I don't need your approval. You will notice that I have made no derogative personal remarks about you, just about your posts.

This is all a great shame, and it is an even bigger shame that Soldar got mixed up in all this, because I know that you are interested in electronic design, and you have some great ideas- I have said so, but it is the nature of your posts and the fact that you will not see reason in many cases, that is the problem.
« Last Edit: February 06, 2019, 06:20:57 pm by spec »
 


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