Author Topic: Portable Low Frequency square wave generator circuit - Solved - page 3  (Read 14174 times)

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Offline LaszloTopic starter

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Hi,

I am a locomotive test engineer and I could use a portable square wave generator which could output a 12Vp-p square wave from 1 to 1000Hz, with an input impedance of 50ohms and of course 50% duty cycle. Reason being, with that signal some trainborne equipment, can be tricked to believe that the loco is running (speedo, WSP etc..)

So I tried relentlessly with my zero electronics knowledge to build up a circuit using a 555 timer ic with very little success. - I could only produce signals with positive peaks, and couldn't get the ac coupling to work, also the best I could achieve is 53% duty cycle. (https://mintelectronics.wordpress.com/2012/06/17/squarewave-generator-using-555/) - Using this circuit.

Tried an LM741 op-amp, but hey, I couldn't even figure it out how to power it up with the dual PSU.

So I gave up and bought this DIY sig gen kit from aliexpress, which works like a charm, but it has an input impedance of a whopping 800 ohms plus. Also, I doubt that it would be beefy enough to provide enough current for my line of work.

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

Laszlo
« Last Edit: May 27, 2019, 09:20:25 am by Laszlo »
 

Offline nsrmagazin

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Re: Portable Low Frequency square wave generator circuit
« Reply #1 on: January 27, 2019, 07:37:29 am »
What is the tolerance on the frequency, duty cycle, voltage and current?

See the circuit for "50% Duty Cycle Astable Oscillator" or "Improved 555 Oscillator Duty Cycle".
https://www.electronics-tutorials.ws/waveforms/555_oscillator.html

With opamps its the easiest.
https://www.electronics-tutorials.ws/opamp/op-amp-multivibrator.html

Can not be done with a single timer555 IC. The timer has a maximum output of "15VDC"(real "12VDC"). Is using a microcontroller an option? It will be easier to switch a transistor or should I say 2 complementary transistors.

Last option is a H bridge(most commonly used, hardest and best).

This thread summarizes the opamp option:
https://www.edaboard.com/showthread.php?292062-Dual-polarity-square-wave-generator
Hi all!
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Offline beanflying

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Re: Portable Low Frequency square wave generator circuit
« Reply #2 on: January 27, 2019, 08:14:56 am »
Few questions. Does it need to be portable or do you have a voltage source available, if you have a source what is it?

I am getting the idea you are looking for +-6V or 12p-p because you use the term ac coupling? Or do you mean you want a 0-12V pulse? Not a big deal either way but it does matter.

To keep it simple and the explanation too (until you give a few more details) an arduino micro with a display of some sort (if needed) driving an output Transistor or FET would give you maximum variation and simple electronics. Now we need to know your power supply options and the output you need :)

The dead simple version with no bells and whistles (bad train pun :palm: ) is a multivibrator such as in this link https://www.electronics-tutorials.ws/waveforms/astable.html

Or re look at the 555 option depending on those couple of questions.
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Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #3 on: January 27, 2019, 10:40:30 am »
Hi,

I am a locomotive test engineer and I could use a portable square wave generator which could output a 12Vp-p square wave from 1 to 1000Hz, with an input [output] impedance of 50ohms and of course 50% duty cycle. Reason being, with that signal some trainborne equipment, can be tricked to believe that the loco is running (speedo, WSP etc..)

So I tried relentlessly with my zero electronics knowledge to build up a circuit using a 555 timer ic with very little success. - I could only produce signals with positive peaks, and couldn't get the ac coupling to work, also the best I could achieve is 53% duty cycle. (https://mintelectronics.wordpress.com/2012/06/17/squarewave-generator-using-555/) - Using this circuit.

Tried an LM741 op-amp, but hey, I couldn't even figure it out how to power it up with the dual PSU.

So I gave up and bought this DIY sig gen kit from aliexpress, which works like a charm, but it has an input [output] impedance of a whopping 800 ohms plus. Also, I doubt that it would be beefy enough to provide enough current for my line of work.
Hi Laszlo,

(I have taken the liberty of altering your original post(OP) above, about inputs and outputs, to express what I think you intended.)

You could use a 555 or possibly the Aliexpress signal  generator to do your job, but it sounds like you would need to add an output driver circuit, which is quite straight forward. But as has been stated, we need to know what power source you are using, battery or mains, I would guess battery in view of the application.  Also, we need to know the positive excursion and negative excursion of the output waveform required from the signal generator. I take it, from what you say, that the input impedance of the units under test (UUT) is 50 Ohms.

My question is whether anyone on this forum knows about a working circuit which I could utilize to build my little project.
Yes: once we know your requirements, we will be in a position to post a complete circuit that will do your job nicely. :)
« Last Edit: January 27, 2019, 11:21:03 am by spec »
 
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #4 on: January 27, 2019, 11:21:53 am »
Hi,

I am a locomotive test engineer and I could use a portable square wave generator which could output a 12Vp-p square wave from 1 to 1000Hz, with an input impedance of 50ohms and of course 50% duty cycle. Reason being, with that signal some trainborne equipment, can be tricked to believe that the loco is running (speedo, WSP etc..)

So I tried relentlessly with my zero electronics knowledge to build up a circuit using a 555 timer ic with very little success. - I could only produce signals with positive peaks, and couldn't get the ac coupling to work, also the best I could achieve is 53% duty cycle. (https://mintelectronics.wordpress.com/2012/06/17/squarewave-generator-using-555/) - Using this circuit.

Tried an LM741 op-amp, but hey, I couldn't even figure it out how to power it up with the dual PSU.

So I gave up and bought this DIY sig gen kit from aliexpress, which works like a charm, but it has an input impedance of a whopping 800 ohms plus. Also, I doubt that it would be beefy enough to provide enough current for my line of work.

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

Laszlo
I think you've got your impedances mixed up. Don't you mean you need an output impedance of 50Ω?

You need some sort of buffer to get the impedance down to the desired level. The TC4420 will do. It has a much lower output impedance than 50R so will need a series resistor on the output.
https://ww1.microchip.com/downloads/en/DeviceDoc/21419D.pdf

Add the MOSFET driver IC to your existing signal generator or build your own using a microcontroller or Schmitt trigger. Another possibility is to build a higher frequency astable and add a frequency divider to get exactly 50% duty cycle.
 
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Offline LaszloTopic starter

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Re: Portable Low Frequency square wave generator circuit
« Reply #5 on: January 27, 2019, 04:50:02 pm »
Hi All,

Apologies for mixing the in and outputs. How foolish. Also, I should have been more precise with the specs so here it is as  it follows:
Amplitude = 12vp-p (+6V -6V )
Output current = 400mA
Adjustable from 1Hz to 1kHz
Output impedance 50 Ohms
Source voltage - can be anything I was hoping it could be done via 2 standard 9vdc batteries. But again, as long as it is reasonably portable I don't mind attaching it to any source :)
Tolerance of frequency is negligible.
Tolerance for duty cycle is +-5%.
Tolerance for voltage is not really good, basically, the output has to be 12Vp-p or slightly higher otherwise the equipment won't recognize the signal.

Unfortunately, the equipment under test is an ancient WSP kit on HST locos, and I haven't got a drawing for it (nobody seems to have it as far as I am aware). So all the above-mentioned specs have been measured by me. Using a multimeter in series to monitor the current, and adjusting the sig-gen to see when does it stops reacting to the input signals.

Back in the olden days when the equipment was new, they used to use an op-amp based test equipment powered by two 9Vdc batteries with an output voltage of 18Vdc, but it won't work anymore as it has been modded to an unknown extent.

I looked at all the suggested the methods, the microcontroller seems to be promising. I think the 555 won't be good because of the limited output current. The op-amp also sounds like a good solution however, I honestly can't get my head around the dual power supply thingy.
In fact, I attempted building that circuit twice by using two 9Vdc batteries and an lm741 but could not get it to work.  I am so advanced, I can't even get my head around of how to limit the 18V source voltage to 12V.
Don't get me wrong, I can build just about anything provided I have a detailed drawing, it is just the lack of understanding which stops me most of the time. :)

Thanks again for the help and links.
 
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Online Kleinstein

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Re: Portable Low Frequency square wave generator circuit
« Reply #6 on: January 27, 2019, 05:30:58 pm »
With the Ne555 or similar the frequency accuracy would be not very good, so maybe 0.5-10 % depending on the adjustment (pot / multi step switches). If much better accuracy is wanted a digital setting (e.g. via µC) is probably the way to go.  There are relatively affordable (e.g. $50-100) Chinese DDS generators (e.g. up to 10 MHz) available, that might be possible to  convert battery operation.

The output specs still don't make much sense:
A +-6 V output with 50 Ohms would deliver some 120 mA (if the 6 V are no load) or 240 mA max. (if the +-6 V would be with 50 Ohms load and thus +-12 V open circuit).
Even this power level is too much for 9 V block cells. An would more like call for some 10-20 AA cells or maybe some 18650 cells.

With a divider at the output the duty-cycle would naturally be very close to 50% - so no problem here. For the low frequencies a divider would be the easier way anyway. So instead of a NE555 I would consider a CMOS4060 chip, which is a simple oscillator and divider in a single chip.
The output driver would likely need to be separate anyway. Here some gate driver chips are a possibility. Alternatively a high power OP might work, especially if the 50 Ohms are realized only virtually to save on the power.
 
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #7 on: January 27, 2019, 05:41:09 pm »
Hi All,

Apologies for mixing the in and outputs. How foolish. Also, I should have been more precise with the specs so here it is as  it follows:
Amplitude = 12vp-p (+6V -6V )
Output current = 400mA
Adjustable from 1Hz to 1kHz
Output impedance 50 Ohms
Source voltage - can be anything I was hoping it could be done via 2 standard 9vdc batteries. But again, as long as it is reasonably portable I don't mind attaching it to any source :)
Tolerance of frequency is negligible.
Tolerance for duty cycle is +-5%.
Tolerance for voltage is not really good, basically, the output has to be 12Vp-p or slightly higher otherwise the equipment won't recognize the signal.

Unfortunately, the equipment under test is an ancient WSP kit on HST locos, and I haven't got a drawing for it (nobody seems to have it as far as I am aware). So all the above-mentioned specs have been measured by me. Using a multimeter in series to monitor the current, and adjusting the sig-gen to see when does it stops reacting to the input signals.

Back in the olden days when the equipment was new, they used to use an op-amp based test equipment powered by two 9Vdc batteries with an output voltage of 18Vdc, but it won't work anymore as it has been modded to an unknown extent.

I looked at all the suggested the methods, the microcontroller seems to be promising. I think the 555 won't be good because of the limited output current. The op-amp also sounds like a good solution however, I honestly can't get my head around the dual power supply thingy.
In fact, I attempted building that circuit twice by using two 9Vdc batteries and an lm741 but could not get it to work.  I am so advanced, I can't even get my head around of how to limit the 18V source voltage to 12V.
Don't get me wrong, I can build just about anything provided I have a detailed drawing, it is just the lack of understanding which stops me most of the time. :)

Thanks again for the help and links.

That still doesn't add up, I'm afraid.

Output current of 400mA, at +/-6V with an impedance of 50Ω doesn't make any sense because it violates Ohm's law I = V/R = 6/50 = 120mA.

You also won't get that kind of current from a little 9V battery for long.

What do you mean by tolerance for frequency is negligible? Does that mean it's critical or not important? Tolerances are normally specified in a fraction of the total value, usually a percentage, so a 1% tolerance at 100Hz, is an absolute tolerance of +/-1Hz.

Since this is going to be powered off a single, isolated power supply and it's working at a low frequency, then you could have a bridged output and a power supply voltage of 6V.
 
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Offline StillTrying

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Re: Portable Low Frequency square wave generator circuit
« Reply #8 on: January 27, 2019, 05:50:58 pm »
I use one of these cheap junk things.
https://www.eevblog.com/forum/beginners/diy-power-supply-129692/msg1720169/#msg1720169

Its output is a transistor with 1k pull-up visible on the back, you'd have to arrange the 50R and +/- output yourself.
.  That took much longer than I thought it would.
 
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #9 on: January 27, 2019, 07:38:19 pm »
Use a low-dropout regulator to get a stable 6V from the battery and a MOSFET driver with an inverting and non-inverting output and some resistors to shift the output of your oscillator to +/-6V.

One of the outputs can be connected to your circuit's 0V and the other to its input. This will only work if the power supply and signal generator are isolated from the circuit under test.
 
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Offline LaszloTopic starter

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Re: Portable Low Frequency square wave generator circuit
« Reply #10 on: January 27, 2019, 10:59:08 pm »
Hi, as per zero 999 states, the 400mA current is rubbish. I don't know how I measured that with my calibrated DM.
The frequency output needs to be accurate to +-5% to simulate reasonably accurate speed.

I know it sounds absolutely dreadful, but I do need a circuit diagram of the whole thing as I have already tried to mesh a few things together with very little success (so far I killed 2 555 timers and my first lm741 had literrally burn't out once i plugged the positive end of the psu)

Do you think that the improved 555 timer desing which had been linked would be good enough for this? But again, how would I ac-couple the output of that, and how could I make that adjustable so it would keep its duty cycle?

 

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Re: Portable Low Frequency square wave generator circuit
« Reply #11 on: January 27, 2019, 11:29:07 pm »
I'd like to suggest you consider an MSP430G2 LaunchPad with Mecrisp forth loaded on it driving a suitable solid state switch.  Super simple to program if you follow the PWM  example in the README.  Cheap too.
 
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #12 on: January 27, 2019, 11:50:03 pm »
Hi, as per zero 999 states, the 400mA current is rubbish. I don't know how I measured that with my calibrated DM.
The frequency output needs to be accurate to +-5% to simulate reasonably accurate speed.

I know it sounds absolutely dreadful, but I do need a circuit diagram of the whole thing as I have already tried to mesh a few things together with very little success (so far I killed 2 555 timers and my first lm741 had literrally burn't out once i plugged the positive end of the psu)

Do you think that the improved 555 timer desing which had been linked would be good enough for this? But again, how would I ac-couple the output of that, and how could I make that adjustable so it would keep its duty cycle?
I agree, you need a complete schematic. You can stitch one together, once you have all of the building blocks in place.

The problem with the 555 timer is it's difficult to get a 50% duty cycle output. Your best bet is a CMOS variant, such as the 7555.

Another option is an astable with a divider to give a square wave. See attached for an example using the 4013 to 74HC74. The potentiometer sets the frequency and the switch changes ranges. I suggest you have at least two, say 1Hz to 30Hz and 30Hz to 1kHz, is getting 1Hz to 1kHz with one setting will be tricky.

This schematic isn't quite complete, hence the lack of component designators. You'll probably need to alter the component values.
« Last Edit: January 27, 2019, 11:53:56 pm by Zero999 »
 
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Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #13 on: January 31, 2019, 09:59:29 am »
HI Laszlo,

Attached is a schematic for a pulse generator to meet your requirements:

It is intended to be powered by a couple of mains to 12V, 1A or more, stabilized power supplies, which are available from many sources at quite a low price. Battery power could also be provided, if required.

The frequency control is by a single potentiometer to sweep from below 1Hz to above 1kHz.

Note that the 555 timer is a CMOS type- an ordinary 555 will not do.

http://www.ti.com/lit/ds/symlink/lmc555.pdf

http://www.ti.com/lit/ds/symlink/ucc21520.pdf

https://www.onsemi.com/pub/Collateral/FDD3672-D.pdf

https://www.onsemi.com/pub/Collateral/FDD3682-D.pdf
« Last Edit: January 31, 2019, 10:13:55 am by spec »
 

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Re: Portable Low Frequency square wave generator circuit
« Reply #14 on: January 31, 2019, 10:26:09 am »
The problem with the 555 timer is it's difficult to get a 50% duty cycle output.
There are several circuit designs with 555 timer that allow anywhere from 0% to 100% duty (with logical limits at both ends of the range) and there is no problem getting 50% duty cycle. OTOH it is easy to start with double the frequency and then divide by 2 and this results in 50% duty cycle exactly always and every time.

This project seems like it could be done very simply with a 555 timer, powered with 6+6 volt split supply or with a single supply and decouple the output with a large capacitor. Insert 50 ohm resistor in line with output and that should cover it.

Depending on where you are going to connect this device you might want to isolate it well, very well or really, really well.
« Last Edit: January 31, 2019, 10:41:15 am by soldar »
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Online Zero999

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Re: Portable Low Frequency square wave generator circuit
« Reply #15 on: January 31, 2019, 11:43:49 am »
The frequency control is by a single potentiometer to sweep from below 1Hz to above 1kHz.

Note that the 555 timer is a CMOS type- an ordinary 555 will not do.

http://www.ti.com/lit/ds/symlink/lmc555.pdf

http://www.ti.com/lit/ds/symlink/ucc21520.pdf

https://www.onsemi.com/pub/Collateral/FDD3672-D.pdf

https://www.onsemi.com/pub/Collateral/FDD3682-D.pdf
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.

R1 is a little on the low side. At 1k, the asymmetric resistances of the output transistors will contribute to the timing, taking the duty cycle away from 50%. It would be better to opt for a higher resistance, such as 10k and have a switch to select between two capacitors for two ranges, say 1Hz to 30Hz and 30Hz to 1kHz. This would also make sense from an ease of use perspective, as 1Hz to 1kHz with a single potentiometer would  be quite difficult to adjust accurately, even with a ten turn pot.

The problem with the 555 timer is it's difficult to get a 50% duty cycle output.
There are several circuit designs with 555 timer that allow anywhere from 0% to 100% duty (with logical limits at both ends of the range) and there is no problem getting 50% duty cycle. OTOH it is easy to start with double the frequency and then divide by 2 and this results in 50% duty cycle exactly always and every time.
It depends on how stringent your 50% duty cycle requirements are. The CMOS variant isn't perfect, as the on resistance of the high and low side output transistors isn't symmetrical. Going from the graphs on the datasheet, when VDD = 5V and a junction temperature of 25oC, the P-MOSFET has an on resistance of 300R and N-MOSFET 60R. It's better if the impedance seen by the output stage is as high as possible.
https://www.nxp.com/docs/en/data-sheet/ICM7555.pdf

In this case, a CMOS 555 timer is probably more than good enough, so long as the output isn't loaded too much. As mentioned above, it has an output impedance of well over 50 Ohm, so will need buffering: a 7555 + 50 Ohm resistor will not do! A MOSFET driver IC can be used to buffer the output.

I'd probably go for a counter + divider IC such as the 4060. It can use a smaller, closer tolerance, higher stability capacitor and the ranges can be switched by changing between different divider outputs. The frequency could be varied between 500Hz to 16kHz, giving 31.25Hz to 1kHz on the Q3 output and 0.97Hz and 31.25Hz on the Q8 output. To take into account for component tolerances, set the oscillator minimum and maximum frequencies to be a little lower than 500Hz and higher than 16kHz: aim for 475Hz to 16.8kHz. Again it will need to be buffered, as the 4060 has far too higher output impedance.

Lots of information about calculating the resistor and capacitor values can be found using a search engine.
https://assets.nexperia.com/documents/data-sheet/HEF4060B.pdf
https://www.brighthubengineering.com/diy-electronics-devices/123626-making-flasher-timer-oscillator-circuits-using-a-single-chip/
https://dmohankumar.wordpress.com/2012/05/13/design-your-circuit-part-ii-cd-4060-timer/
« Last Edit: January 31, 2019, 11:48:14 am by Zero999 »
 
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Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #16 on: January 31, 2019, 12:17:18 pm »
It depends on how stringent your 50% duty cycle requirements are.
Yup. I am assuming "not too stringent". Again, a divider solves that issue if needed.

In this case, a CMOS 555 timer is probably more than good enough, so long as the output isn't loaded too much. As mentioned above, it has an output impedance of well over 50 Ohm, so will need buffering: a 7555 + 50 Ohm resistor will not do! A MOSFET driver IC can be used to buffer the output.
The traditional bipolar version will source or sink up to 200 mA with a little voltage drop at each end which may be admissible or can be compensated with a bit higher supply voltage.

In other words, you can make something better and more complex but if you want something quick and dirty which will work I think a single bipolar 555 will do it. A split supply of 7.5 + 7.5 volts and very few more components.

I would make sure where it is being connected to because ... people.

I use bipolar 555 timers because I have a stock of them enough to last me several lifetimes. :)


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Re: Portable Low Frequency square wave generator circuit
« Reply #17 on: January 31, 2019, 01:28:45 pm »
The split power supply should be asymmetrical to match the saturation voltages of the bipolar 555.

How would you get the duty cycle to 50%, with an adjustable frequency from 1Hz to 1kHz, using the plain old bipolar 555?
 
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Re: Portable Low Frequency square wave generator circuit
« Reply #18 on: January 31, 2019, 02:32:32 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.

 
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Offline soldar

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Re: Portable Low Frequency square wave generator circuit
« Reply #19 on: January 31, 2019, 02:36:41 pm »
The split power supply should be asymmetrical to match the saturation voltages of the bipolar 555.
Back to "not too stringent" because if we are talking "stringent" then, yes, there are better, more sophisticated, designs. I am guessing the input is for some counting circuit which is "not too stringent" and will accept a certain range. If we have strict requirements then we need a stabilized power supply because batteries will not do.

How would you get the duty cycle to 50%, with an adjustable frequency from 1Hz to 1kHz, using the plain old bipolar 555?
Well, there are several circuit designs which produce a 50% duty cycle and where the on time and down time depend on the same resistor, like 50% Duty Cycle Astable Oscillator halfway down the page. Vary R2 and the period changes but the duty cycle shouldn't.

Again, this is a quick and simple solution, not the best or most sophisticated. I think it would be enough for this type of application though.
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Re: Portable Low Frequency square wave generator circuit
« Reply #20 on: January 31, 2019, 02:46:01 pm »
+ Laszlo

If you are still around please look at your PM inbox.
 
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Re: Portable Low Frequency square wave generator circuit
« Reply #21 on: January 31, 2019, 03:00:06 pm »
... an adjustable frequency from 1Hz to 1kHz ....
I would spread this over three switchable ranges because over a single range I think it is too much and you get not enough ability to set a precise frequency. 1 to 10 Hz, 10 - 100 Hz and 100 to 1000 Hz.
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Re: Portable Low Frequency square wave generator circuit
« Reply #22 on: January 31, 2019, 03:17:26 pm »
[Again, this is a quick and simple solution, not the best or most sophisticated. I think it would be enough for this type of application though.
What a presumptuous fellow you are. >:(

As I have said before to all you armchair 'experts': Let us see your complete circuit, embodying all these wonderful ideas that you have.
« Last Edit: January 31, 2019, 03:44:09 pm by spec »
 
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Re: Portable Low Frequency square wave generator circuit
« Reply #23 on: January 31, 2019, 03:33:05 pm »
... an adjustable frequency from 1Hz to 1kHz ....
I would spread this over three switchable ranges because over a single range I think it is too much and you get not enough ability to set a precise frequency. 1 to 10 Hz, 10 - 100 Hz and 100 to 1000 Hz.
Do you really think that I haven't thought of all this stuff. I was hoping that the usability could be discussed with the OP. Anyway, if I had posted my circuit with range switching, that would have been a golden opportunity for you to say it is too complicated and expensive and it could be done with one pot and one capacitor.

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
« Last Edit: January 31, 2019, 03:36:18 pm by spec »
 

Offline spec

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Re: Portable Low Frequency square wave generator circuit
« Reply #24 on: January 31, 2019, 03:40:43 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.

Had I posted a circuit with a precision oscillator and exact 1:1 mark to space ratio, you could imagine what the comments would have been then ... to complicated- I would have done it with a 555. |O
« Last Edit: January 31, 2019, 03:48:11 pm by spec »
 
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