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Simple Waveform Generator Help

bigkim100

Apr 17, 2013
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https://www.instructables.com/THE-SIMPLEST-FUNCTION-GENERATOR-BUILT-ON-A-BREADBO/

This is an article about making a single chip Function Generator
Only the first stage is adjustable. How do I adjust the 2nd 3rd and 4th generator in it, or can I?
Where can I add pots for that stage?
Can the amplitude of its output also be adjusted??
I can only guess that since the lm324 power requirements are listed as 3-32vdc, amplitude can be adjusted via the power supply in????????

Thanks in advance for any help given
-Kim
 
Last edited:

AnalogKid

Jun 10, 2015
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First, the bad news. He shows the circuit running on a single 9 V battery. It will not. It needs both plus and minus supplies. This can be two 9 V batteries in series, with the common point as the circuit ground. Note that there is no ground symbol anywhere in the schematic. This tells us a lot about the design and the designer. The schematic in the comments section is much better.

You do *not* adjust the signal amplitude by varying the power supply voltage. On paper it will work, but in practice it can introduce clipping and other distortions.

Each of the three signal output points is an opamp output, which is a low impedance point. You can add three pots, one at each signal output to GND, to give you independently adjustable outputs. The pots should be 10 K or higher. Note that the pot value also is determined by what the load on the wiper is. IOW, what the variable output is driving.

Now, about the circuit ... This is not a good one. The problem is that there is no feedback from the triangle output to the square wave generator. Without that, as you adjust the square wave frequency the amplitude of the triangle wave will change. At low frequencies, the peaks of the triangle might be clipped. Also, unless the components are *perfectly* matched, the integrator output will acquire a DC offset that eventually will be so large that the opamp output is saturated and there is no signal. Both issues can be fixed by rearranging the two circuits. More on that later.

The third stage is a single-pole lowpass filter. Because it is not adjustable, its filtering action (rounding the triangle into a sine) will vary with frequency. This is much more difficult to fix.

The fourth stage is a simple output buffer. It is ok as is, although I would have gone with a non-inverting gain stage so the sine phase is the same as the other two waveforms and the amplitude is closer to that of the other waveforms.

Here are links to better triangle/square circuits:

http://www.interfacebus.com/triangle-wave-oscillator-circuit-schematic.html

https://saaqibs.blogspot.com/2014/09/triangle-square-wave-oscillator-circuit.html

https://forum.allaboutcircuits.com/...ing-a-simple-triangle-wave-oscillator.156475/

http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm

ak
 
Last edited:

Audioguru

Sep 24, 2016
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The old LM324 quad or LM358 dual opamp makes a mess of waveforms:
1) Lots of noise.
2) Crossover distortion on sine and triangle waves.
3) Low and distorted output level on frequencies above about 3kHz.
 

bigkim100

Apr 17, 2013
224
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Messages
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The old LM324 quad or LM358 dual opamp makes a mess of waveforms:
1) Lots of noise.
2) Crossover distortion on sine and triangle waves.
3) Low and distorted output level on frequencies above about 3kHz.
Thank you very much AudioGuru
 

bigkim100

Apr 17, 2013
224
Joined
Apr 17, 2013
Messages
224
First, the bad news. He shows the circuit running on a single 9 V battery. It will not. It needs both plus and minus supplies. This can be two 9 V batteries in series, with the common point as the circuit ground. Note that there is no ground symbol anywhere in the schematic. This tells us a lot about the design and the designer. The schematic in the comments section is much better.

You do *not* adjust the signal amplitude by varying the power supply voltage. On paper it will work, but in practice it can introduce clipping and other distortions.

Each of the three signal output points is an opamp output, which is a low impedance point. You can add three pots, one at each signal output to GND, to give you independently adjustable outputs. The pots should be 10 K or higher. Note that the pot value also is determined by what the load on the wiper is. IOW, what the variable output is driving.

Now, about the circuit ... This is not a good one. The problem is that there is no feedback from the triangle output to the square wave generator. Without that, as you adjust the square wave frequency the amplitude of the triangle wave will change. At low frequencies, the peaks of the triangle might be clipped. Also, unless the components are *perfectly* matched, the integrator output will acquire a DC offset that eventually will be so large that the opamp output is saturated and there is no signal. Both issues can be fixed by rearranging the two circuits. More on that later.

The third stage is a single-pole lowpass filter. Because it is not adjustable, its filtering action (rounding the triangle into a sine) will vary with frequency. This is much more difficult to fix.

The fourth stage is a simple output buffer. It is ok as is, although I would have gone with a non-inverting gain stage so the sine phase is the same as the other two waveforms and the amplitude is closer to that of the other waveforms.

Here are links to better triangle/square circuits:

http://www.interfacebus.com/triangle-wave-oscillator-circuit-schematic.html

https://saaqibs.blogspot.com/2014/09/triangle-square-wave-oscillator-circuit.html

https://forum.allaboutcircuits.com/...ing-a-simple-triangle-wave-oscillator.156475/

http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm

ak
Thank you very much AnalogKid
 

bigkim100

Apr 17, 2013
224
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Hello,

Do you mean an arbitrary waveform generator?
That can be quite complex.
https://www.google.com/search?q=arb...lient=img&ei=DdbJYugXkdOTBbKetMgH&safe=images

Bertus
Is it possible to do it in a sloppy analogue wave having a 555 driving a 4017, stepping thru various resistors that change the output. This would be only semi-random, with low quality components to make the selection relatively random.
To answer this, you will need to step into my analogue-driven fevered mind...lol
 

AnalogKid

Jun 10, 2015
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Is it possible to do it in a sloppy analogue wave having a 555 driving a 4017, stepping thru various resistors that change the output.
A more common approach from the 70's is to use an 8-bit shift register instead of the Johnson counter.

ak
 

bigkim100

Apr 17, 2013
224
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Bertus, this takes me back to my youth building circuits from Elementary Electronics Popular Electronics and ETI (when I could find it).
The Pinnacle of ,my building from then at 9 years old was a Fluorescent alarm Clock , that used display tubes from Jameco and a huge IC that cost me a fortune at the time, and its static sensitive nature scared me silly. It still sits in my closet to this day waiting its reawakening.
 

bigkim100

Apr 17, 2013
224
Joined
Apr 17, 2013
Messages
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I remember the ETI Canada, that was actually a reprint of ETI EUs edition, with absolutely no consideration if parts were available in Canada. They published a beautiful Ozone generator, that used a Torroid to generate the voltages needed back in the day when Torroids were not generally used that much, and I wanted to give one a try. I called the Canadian Distributor of he Torroid, and they had no idea that their coils had been used in the article, and they were not available in North America, as the writer had not bothered to even contact them regarding availability. It was a true Head-Slapping moment.
 
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