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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Wheel of fortune
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synaesthesia



Joined: May 27, 2014
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PostPosted: Fri Jun 27, 2014 2:36 pm    Post subject: Wheel of fortune
Subject description: Another random melody generator
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Hello, after following this forum for quite a while it is now time to contribute myself. Thanks to all for the great ideas I found here.

The schematic below is my attempt at something similar to a rungler. It generates an endless sequence out of 8 possible tones. Only two chips are needed, a 4093 for the oscillators and the pulse, and a 4520 for the divider and R2R network that drives the GDAL VCO. The speed of the sequence can be adjusted.

It works like this: the LFO generates a square wave that in turn generates a very short pulse of about 1ms. The pulse enables a high frequency clock to briefly go to a counter. At the end of the pulse the HF clock is disabled and the Count&Hold keeps the current counter value. This value determines the voltage of an R2R network that drives a VCO which generates the tone. The randomness comes from the HF clock that never really gives the exact same number of clock pulses to the counter during the pulse.

Here is the schematic and sound file. Sorry for the poor quality, it is recorded directly from a built-in laptop microphone. Enjoy!


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commathe



Joined: Jul 26, 2013
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PostPosted: Fri Jun 27, 2014 9:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice! This reminds me of something very similar I was doing in Max/MSP a while back where I would use one or more lfos to increase a counter that would reset itself and output the total upon receiving a pulse. I liked the glitched out screech sounds you got from driving the pulse really fast too.

Very cool little circuit! I like how self contained it is. I also like the really simple vco you have there! Definitely going to consider stealing that!
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analog_backlash



Joined: Sep 04, 2012
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PostPosted: Sat Jun 28, 2014 4:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi synaesthesia and welcome

A really nice little circuit. I like the way the randomiser works - I'll have to give that a go sometime. Up until now, I've only used 4006s to give a pseudorandom sequence and these are obsolete now (although there are other shift register circuits on the forum, e.g. using 4015s). This looks like a nice & easy alternative.

I hope JingleJoe appreciates the use of his GDAL VCO Very Happy

Keep up the good work,

Gary
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PHOBoS



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PostPosted: Sun Jun 29, 2014 3:54 am    Post subject: Reply with quote  Mark this post and the followings unread

welcome party!

I got a question about your HF oscillator, what is [P] connected too ? I'd expect a very small capacitor to ground.
Now if you breadboarded it then the breadboard could have provided that capacitance. Which makes me wonder if
you could use U1b for the HF oscillator with [P] being pin 6, since it's located next to GND (pin 7). So maybe
the pins or solderpads would create a small capacitance aswell.

It reminds me a bit of the circuit I used for the RGB shroom synth & drums, which also works of randomness
created by using an oscillator with a high frequency combined with an LFO. Be it that I used a shiftregister
and it doesn't work in the same way Wink



nice circuit Very Happy

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synaesthesia



Joined: May 27, 2014
Posts: 61
Location: Germany
Audio files: 17

PostPosted: Sun Jun 29, 2014 8:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the feedback! Yep, the VCO is JingleJoe's design. That's why I labeled it appropriately as GDAL VCO Smile I changed the series resistor from the R2R and added the diode and pull-up resistor to keep the base at around 680mV which works better in my circuit.

PHOBoS, you are exactly right. The condensator is missing deliberately. Currently the maximum switching speed of the CMOS gate actually limits the HF frequency. I experimented with several capacitors and diodes instead of the resistor. No combination I tried so far gave me the slightly unstable HF frequency that I want to have there.

What I observed is that after not touching the circuit for 15 minutes or so it sometimes finds an equilibrium and the clocks per pulse stabilize a bit. That leads to a shorter and repeating sequence of tones. An open point [P] with a short wire attached, or simply touching [P] briefly destabilizes it and the sequence is more random again. I am sure that the fact that the circuit is still on breadboard helps also.

I am experimenting with feeding back Q1 of U2A to P, but so far neither a 1M resistor nor a small cap worked reliably. Maybe the pulse length could somehow be influenced to make sure the circuit remains sufficiently unstable.

Ideas anyone? Question
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analog_backlash



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PostPosted: Sun Jun 29, 2014 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi again.

Just noticed that R6 should be a 22K really for the 'tail' of the R/2R ladder (i.e. R6 should have the 2R value). I made the same mistake on my first R/2R circuit. It won't make much difference to your problem though... I'm quite surprised that the circuit settles to a regular(ish) pattern after a while, given the high frequency that you're clocking it at. As I say, I'll have to try it myself to see what happens.

Another possibility - you could try experimenting with a 74HC132 instead of the 4093 (since you're working at 5V anyway) as this can run faster, but then would the 4520 be able to keep up with it?

Gary

P.S. My GDAL VCO remark was not a criticism (I probably worded it badly), it's just that we hear very little from him lately and I thought he might be pleased to see the circuit being used Cool
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commathe



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PostPosted: Sun Jun 29, 2014 6:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

You could try "poisoning" the ground a la the cacophonator. Make your LFO also drive a large-ish capacitive load to ground (10uF+). This will affect the stability of all the oscillators though so it will also make the sequence less even. This is unless you are using bypass caps, in which case it wont work.
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synaesthesia



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PostPosted: Tue Jul 01, 2014 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the suggestions. I think I found a solution for a better randomization. Here is an updated schematic.

First, I have simplified the R2R ladder a bit to save a few components. This is no precision instrument, right? This has the side effect of changing the generated frequencies slightly.
Second, I am feeding back Q1 from the Count&Hold to the pulse generation via a small cap. This seems to do the trick. I get less frequent repetitions now and the distribution of the counter values has improved.

I captured the voltage at the transistor base at a very high sequence speed (~2KHz) to compare the original design to the update. The old design wasn't really that bad, I chose a worst case snapshot.
As you can see, the voltage levels are now jumping more often and there are less repetitions. It certainly isn't really random, but good enough for me.


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analog_backlash



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PostPosted: Tue Jul 01, 2014 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi synaesthesia.

Glad that you've improved the randomness. I have breadboarded the original WOF and I see what you mean about it falling into patterns (although our brains like to find patterns where there are none, so it can be tricky Confused ). I'll convert it to the new WOF circuit and see how it sounds. Yes, my R/2R comment really only matters for a precision device. I assume that the HF oscillator is still working on stray capacitance. I did try mine with a very small capacitor to ground, but it didn't seem to make much difference really.

Gary
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synaesthesia



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PostPosted: Fri Jul 04, 2014 11:41 am    Post subject: Sequencer Spinner Reply with quote  Mark this post and the followings unread

Here is a variant of the WOF circuit. This time the circuit is meant to repeat a sequence of 16 notes. The sequence can be randomized by pressing a button. When the button is open, the last bit of the bit pattern through the shift register is inverted and fed back into the shift register. That generates a sequence of 16 repeating states. When the button is pressed, a random bit is inserted in the shift register instead.
Each note in the sequence is derived by using 3 of the shift register outputs. However, the order of the notes in the sequence is never random and not all possible sequences of 16 notes will occur. I believe this is similar to the Benjolin or the Rungler.
Nevertheless, the sequences are interesting to listen to and I have added a sound file. The first 18 seconds are recorded with one repeating sequence and the speed is increased over time. Then the randomize button is held to continuously change the generated sequence and the speed is increased again (pausing for an extra long time to listen to the nice glitch sounds at high speed that many of us enjoy).


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PHOBoS



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PostPosted: Mon Jul 07, 2014 3:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

love it. Very Happy

If you would replace U1b with an XOR you got a mini Turing machine.
(and if you make a discrete XOR with a bridge rectifier like here you don't need an extra chip)

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synaesthesia



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PostPosted: Tue Jul 08, 2014 11:44 am    Post subject: Reply with quote  Mark this post and the followings unread

A real turing machine! Well, what an intriguing idea... if I make that shift register really, really long... I could build...
- no, must stop that thought! Been there, done that. Smile That's why I have so many TTL and CMOS chips left, waiting for a new life in lunetta circuits.

With regard to the turing machine module at the link, saw that and I like it. I chose a NAND because I wanted it to work as an inverter to double the sequence length. Of course an XOR could act as an inverter too. So not sure if it would make a big difference in this circuit.
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