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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Pimp my squarewave
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synaesthesia



Joined: May 27, 2014
Posts: 59
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PostPosted: Wed Jul 09, 2014 11:15 am    Post subject: Pimp my squarewave
Subject description: because squarewaves can be boring
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Working mostly with digital circuits in my Lunetta experiments, I sometimes wish for some beefier sound than that of the typical squarewaves. Of course, I could start adding filters to make the resulting sound a bit more interesting. Here is an attempt to do it the digital way. It extracts harmonic frequencies from the original signal and adds them together again.

What the circuit does is extracting the rising and falling edges of the input signal (a squarewave) using the two RC pulse generators and combining the pulses to the doubled input frequency. That one is then divided by three using a Johnson counter. The original frequency is also divided by three. Then it adds the original frequency, the frequency*2/3, the frequency*2 and the frequency/3 together for the output signal. The ratio 2:3 is that of the equal tempered perfect fifth and the ratio 1:2 is the octave. So no matter what the input frequency is, the output frequencies will be harmonic.

Because of the 10 nF condensators used, the output waveform looks rather symmetric in a range from 300...1500 Hz. Above that the pulses become too long and the waveform starts to degenerate. Using 1nF condensators instead moves that point to about 5 KHz. Anyhow, that's not a problem. You will note that only if you sweep through the frequency range. One interesting effect is when you sweep above that point and then down again. The generated waveform will suddenly look different, but sound similar. This is because the two Johnson counters get out of sync. Again, not a problem, but interesting to note.

The result is a somewhat more interesting sound than that of the original squarewave. In the current circuit the frequencies are mixed using the same resistor values. Using pots instead would allow to attenuate individual frequencies in the output signal and by that change the color of the sound somewhat. Soundfiles to follow soon.

Ultimatively I am looking for a circuit that changes my input frequency, but only slightly. So I could add it to the original signal and get those beautiful interferences. Haven't been successful with my experiments in that direction yet. Any suggestions are welcome.


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synaesthesia



Joined: May 27, 2014
Posts: 59
Location: Germany
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PostPosted: Wed Jul 09, 2014 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Pictures:
(1) the input square wave (below) and the generated output waveform
(2) above 2KHz the peaks of the output waveform start to fall together
(3) after sweeping down again, a slightly different waveform is generated


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synaesthesia



Joined: May 27, 2014
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PostPosted: Wed Jul 09, 2014 11:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Sound file:
(1) the input squarewave (about 360 Hz)
(2) the four frequencies (120, 240, 360, 720 Hz)
(3) all four mixed together
(4) sweeping up and down again


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synaesthesia



Joined: May 27, 2014
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PostPosted: Wed Jul 09, 2014 12:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

For this I changed one of the dividers from a /3 to a /5 by connecting 4093 pin1 to 4015 pin2 instead of pin12. Still a harmony, but more interesting in the resulting mix.


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commathe



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PostPosted: Wed Jul 09, 2014 4:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice! When you keep posting gems like this I'm starting to get very excited every time I see your screen name.

As to changing the input frequency only slightly, have you tried phase locked loops? Look into the 4046. You could try something like multiplying the frequency by 5 then dividing it by 4? Or by 9 then 8?

Try looking at the Schumann PLL schematic:
http://i214.photobucket.com/albums/cc196/digi2t/Schumann%20PLL/Schumann_PLL_update_zps83bc1261.png
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synaesthesia



Joined: May 27, 2014
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PostPosted: Wed Jul 09, 2014 11:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I was thinking about the 4046 and placing a divider in the feedback loop to make it a multiplier. That would give a new frequency close to the original one. Something I will try as soon as I am done with my Lunetta-Lab board. However, even a 9:8 ratio will result in a fixed frequency, and this will result in a fixed beat frequency for the interference. It would be nice to have this beat frequency actually changing slowly.

Right now I am looking in dynamically changing the divider ratios to see if that adds a nice flavor to the sound. Stay tuned.
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PHOBoS



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PostPosted: Fri Jul 11, 2014 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

synaesthesia wrote:
Yes, I was thinking about the 4046 and placing a divider in the feedback loop to make it a multiplier. That would give a new frequency close to the original one. Something I will try as soon as I am done with my Lunetta-Lab board. However, even a 9:8 ratio will result in a fixed frequency, and this will result in a fixed beat frequency for the interference. It would be nice to have this beat frequency actually changing slowly.

I think it's possible to use the 4046 in such a way that it keeps correcting the frequency but never really locks on to it. Maybe that would work.
Very nice ciruit btw Very Happy

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synaesthesia



Joined: May 27, 2014
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Location: Germany
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PostPosted: Fri Jul 11, 2014 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks commathe and PHOBoS. I definitely will try a 4046 later.
I guess my current experiment is just for the records. I added a 4052 as a sequencer to step through 4 combinations of 2 frequencies and clocked it by the input frequency/8. The chopper effect dominates and there is no such thing as a beat frequency. Not worth posting. Sad However, when clocked with 20 Hz a nice arpeggio of those 4 tones is generated. That could be useful at some time.
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PostPosted: Fri Jul 11, 2014 4:51 pm    Post subject: Re: Pimp my squarewave
Subject description: because squarewaves can be boring
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synaesthesia wrote:

Ultimatively I am looking for a circuit that changes my input frequency, but only slightly. So I could add it to the original signal and get those beautiful interferences. Haven't been successful with my experiments in that direction yet. Any suggestions are welcome.


Variable delays and then mix? It is not so hard to get some lag on squares, but it will have a workable frequency range too ... not sure if you could get enough delay that way easily

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synaesthesia



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PostPosted: Sat Jul 12, 2014 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Okay, this one is a bit better. It delays the falling or rising edge of the input squarewave via an RC network. R would normally go to Vdd or GND, but it goes to a resistor network connected to the outputs of a 4-bit Johnson counter instead. The changing voltage at that point varies both the delayed edge and the delay. The beat frequency is f/8 then, which is pretty fast. Sound file is attached. The first few seconds with the input squarewave, then the output signal while sweeping the input frequency up and down.

There are a few variations possible. You could add an inverter and build separate delays for the falling and rising edges. Tried that and it wasn't much better. You could also use the second half of the 4520 to build another Johnson counter and divide the input frequency down by 8 before it shifts the counter with the resistor network. Gives you a beat frequency of f/64. But that was a bit too slow. Simpler is better, I prefer the first version.


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PostPosted: Sat Jul 26, 2014 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Still messing around with the idea to turn a simple square wave into something more interesting. I wondered what happens if you divide the original frequency by two for three times and then combine the three divided frequencies again? If you keep the order and use the weights 1,2,4 you should get a staircase ramp with 1/8 the original frequency. Ok, what happens if you recombine them with other weights? You should get other stepped waveforms.

I wanted to know how these sound and put together the following small circuit. It uses the 4060 to generate a high frequency that is then divided down. The first three divider output stages are fed through a 4053 which combines them again via three resistors with ratios 1:2:4. The 4053 changes the order of the first three frequencies controlled by the last three divider outputs of the 4060.

The generated waveforms should look similar to the waveforms in the image below. The image was actually generated using a spreadsheet and has smoothed lines. The real waveforms will repeat for much longer and will look like staircases. Each waveform has the same period, but the dominant frequency changes depending on how the divided frequencies are recombined.


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