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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
lunetta theremin harmonizer effect
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Gordon Charlton



Joined: Oct 07, 2006
Posts: 75
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PostPosted: Tue Aug 31, 2010 4:02 am    Post subject: lunetta theremin harmonizer effect
Subject description: luneffecta tharmominizer?
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I'm totally encouraged by building a cacophonator, so I'm ploughing ahead towards my first goal - to build a lunetta based theremin effect box - something that will allow me to play chords on my decidedly monophonic instrument.

I have a deadline. I'm organising a big theremin event in the UK at the end of July next year and there are two proper theremin electronics wizards developing theremin specific effects (all hush-hush and top secret at the moment) that will be demonstrated there. I plan for my humble contribution to be the third effect in the set.

If it works. Eek. I'm a bit nervous about that bit, so I'm kind of hoping you lovely folk will look kindly upon my newbie stumblings and keep me from going hopelessly wrong. Laughing

So far I have a block diagram (attached) and a bunch of links to threads in this forum to read in detail and/or follow closely.

Working backwards, I'll start with the mixer. My next step will be to build a heterodyne space explorer and feed the output through the volume loop of my (adapted) etherwave to see how it sounds and if the output levels are good etc.

http://electro-music.com/forum/topic-40991.html

Next comes the frequency divider and then the multiplier. This thread seems to be the key...

http://electro-music.com/forum/post-168403.html

If I understand the circuit that bugbrand posted correctly, the divider is just a 4017B and a ten-way switch. (Where do I find one of those? Maplin has 12-way rotaries - which would do - but I'd rather have just the right number!)

I can test that with one of the oscillators on the heterodyne space explorer.

Then I can build the full circuit to make a multiplier and test it the same way.

Finally I'll look at taking the non-square-wave-but-still-very-simple-waveform, non-logic-level output from my theremin (at a constant volume with pot-adjustable amplitude - that's another mod I had made to it) and making it square-wave and logic-level.

I'm putting that bit off until last because I'm the most puzzled about it. I guess it is the simplest part really, but the more I google on the subject the more confused I get. I'm definitely watching this thread though. Hopefully that'll get me sorted.

http://electro-music.com/forum/post-305987.html


So. My first question (apart for the one about ten-way switches) is - does this sound sensible or should I totally rethink it?


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tjookum



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PostPosted: Wed Sep 01, 2010 1:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Welcome Gordon! I hope you'll love this place as much as I do.

Quote:
So. My first question (apart for the one about ten-way switches) is - does this sound sensible or should I totally rethink it?

Well thank you for making the effort of making a block diagram but Im going to need some more information. Will it be a standalone device? What sounds do you want? Are you going to do the hand sensing with ldr's or infrared?.

In lunetta terms anything is fair game, wherever there is a variable resistor you can replace it with an ldr. For example the hetrodyne space explorer works great with just ldr's instead of pots.
If you want to make something simple controlled by hand motion I would personally suggest a melodygenerator:
http://electro-music.com/forum/topic-42552.html
Normally you would use 1 fast clock at audio rates for the Input and 3 slower rate clocks to control the ABC. You can also get away with 2 clocks and a CD 4024, then you would use 1 fast clock for the input and the other goes to the clock in of the 4024. Then you have the option of choosing divisions to power the ABC input wich can give very nice melody's.

For super easy and fast, just swap one of the pots on the cacophonator for a ldr. A cool trick to make it better controllable is to add a 2 inch piece of heatschrink tubing and stick the ldr in the bottom end Rolling Eyes , this way it's only affected by light wich comes from directly above.



Quote:
Next comes the frequency divider and then the multiplier. This thread seems to be the key...

http://electro-music.com/forum/post-168403.html

Thanks for that link! Never seen that before and sounds like a fun thing to try with a 4018.

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Gordon Charlton



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PostPosted: Wed Sep 01, 2010 2:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

tjookum wrote:
Welcome Gordon! I hope you'll love this place as much as I do.


Thank you. I've been (mostly) lurking for a while now and it is a fascinating forum - even if a lot of it is way over my head.

Quote:
Will it be a standalone device? What sounds do you want? Are you going to do the hand sensing with ldr's or infrared?.


Ah. I've done that thing where I know what I'm talking about and then assumed other people magically do too, haven't I!

OK, here it is from the top down. I have a heavily modified Moog etherwave theremin. Basically it's an oscillator (specifically a beat-frequency oscillator, controlled by capacitive proximity sensing via the pitch rod) followed by an op-amp (controlled via the volume loop.) It also has some limited wave-shaping circuitry to allow it to play a small range of timbres.

One of its modifications is that I can feed the audio signal generated by the oscillator out of the theremin and into an external device (such as the one proposed here) to modify the waveform, and then back into the theremin and through the theremin's op-amp. This allows me to extend the range of timbres beyond those built into the instrument.

(Incidentally, the reasons for wanting to put effects before the op-amp rather than just chaining them after the regular audio out are the (1) some of my effects boxes have noise gates and (2) some have a constant volume output. In both cases, "yeuch! - not good for my purposes.")

So... I have an external audio source, producing a nice simple single-pitch waveform of constant amplitude - not quite a sine-wave, but still simple enough that it can easily be turned into a square wave of the same frequency.

That's what goes into the audio-in on my block diagram.

What sounds do I hope for? A nice mix of four square waves, all harmonically related, (i.e. just intonation chords) and derived from the pitch of the external oscillator (my theremin) at a constant volume determined by the pots in the mixer section. (For instance, if one of the multiplier/divider pairs multiplies the frequency by 6 and divides it by 5, the output will now be a just minor third higher than the input.)

(On a historical footnote, Prof Lev Termen planned to extend the functionality of the theremin to play chords, but circumstances prevented him from getting around to it. It was mentioned in the original patents.)

Also to generate lo-fi approximations to other waveforms and lower the playable range of the theremin. For instance, setting the multipliers to 1, 3, 5 and 7 and adjusting the mixer pots to appropriate levels could give a very jaggy approximation of a triangle wave, and setting all the dividers to 4 would drop the pitch a couple of octaves.

What limitations do I anticipate? Difficulties tracking the pitch of the theremin signal at either particularly high or particularly low frequencies, and during rapid changes in frequency. I'm OK with this. :-)

I also note that, while my goal is very specific, I see no reason why any suitably simple audio signal could be processed by the device - not just theremins. (And {*evil laugh*} I'm certainly going to be feeding it unsuitably complex audio signals too, to see if I can induce some old fashioned sonic madness from it. Also I'll be giving it a starve pot...)

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MirlitronOne



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PostPosted: Wed Sep 01, 2010 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Dear Gordon

Fancy you not e-mailing your friendly electronics guru!

For starters, re. the 10-way switch - if you buy a 12-way switch, it comes with a locking collar that can restrict the number of selector points for anything from two to twelve, so you can set it to ten. But buy it from Rapid, not Maplin!

Phil

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Gordon Charlton



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PostPosted: Wed Sep 01, 2010 5:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Phil,

(This is the wonderful man who taught me to solder! It's all his fault.)

Don't be offended! I've already had so much good advice from you. I thought I'd give other people a chance...

A one pole twelve way switch with locking collar? Sounds kinky. Shocked

I didn't see it when I looked in Rapid. Found it now. Don't know how I could have missed it. It doesn't mention the collar. Good to know about it.


BTW - correction - looking at the circuit diagram for the multiplier again, I meant 9-way. Just assumed he would have numbered from zero.


PS. Phil - did you see the link I posted elsewhere with audio from the cacophonator? Here it is again -
http://soundcloud.com/beat-frequency/cacophonator-1

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PostPosted: Thu Sep 02, 2010 12:33 am    Post subject: Reply with quote  Mark this post and the followings unread

No offence taken, Gordon.

The locking collars that come with most multi-way rotary switches are a closely-guarded secret known only to the Inner Magic Circle and Opus Dei of the electronics world. My life is in danger as I reveal their secret...

If you take off the mounting nut and lock washer from the threaded shaft (ooh er missus) you will find a small metal ring under the washer. Closer examination by the impossibly eagle-eyed will reveal that this ring sits in a groove with the numbers 1 to 12 engraved in tiny numerals visible only to Santa's elves. Use an elvish screwdriver to gently prise out the ring, then curse and spend the next ten minutes on your hands and knees paying homage to the gods of electronics as you try to find the ring on the carpet - a powerful magnet may help here, as well as revealing that resistor you lost last week. The underside of the ring has a small raised tab on its edge which fits into one of the teeny weeny slots alongside the engraved numbers on the switch body. This restricts the number of click points of the (up to) twelve-way switch. You have now discovered the secret of the locking collar as well as joined the fellowship of the ring.

I have never seen this secret revealed in any book or magazine; I discovered it by chance. Yes, I do have several early projects where the rotary switch features positions that do nothing.

Remember: you ain't seen me, roight?

PS. As per your original post, your idea looks good to me. I'll have a scan around for a suitable sine-ish-to-square converter; there are lots of different ways to achieve this.

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Gordon Charlton



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PostPosted: Thu Sep 02, 2010 5:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Now that is sneaky. I hazard that other, lesser rotary switches in the same range bear a striking internal similarity to the 12 way, other than fewer connection points and a different setting of the elvish ring.



Or I could use the redundant settings to trigger a concealed klaxon. Twisted Evil

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PostPosted: Thu Sep 02, 2010 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

The other switches in the range are not usually "lesser" - generally they differ only in the number of output terminals and the design of the internal connecting rotor to allow 12x1, 6x2, 4x3 and 3x4 selection options. Yes, they all possess the precious elvish ring to restrict the number of setting positions to only those required.

Good idea re. the klaxon - I remember how effectively you used the hidden fire alarm trigger at Hands Off 2007 to divert the audience away from difficult question-and-answer sessions. Laughing

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PostPosted: Thu Sep 02, 2010 8:21 am    Post subject: Reply with quote  Mark this post and the followings unread

MirlitronOne wrote:
I discovered it by chance.


I discovered it by chance, also. When I was mounting one of them I inadvertantly knocked the locking collar out of the holes and discovered (much to my delight) that the collar allows one to select the number of positions.

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PostPosted: Thu Sep 02, 2010 8:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Gordon,

Suggest that you start out by building the divider first. Even with just one divider, you can get some cool (phat) sounds.

You may want to check out the Yusynth dividers... you may be able to adapt them to your purpose.

http://yusynth.net/Modular/EN/DIVIDER/index.html

I've built them and they are really nice. Since they utilize Schmitt triggers for the input it will convert your theremin waveform to a logic signal.

I've never clocked them at audio frequency but I'll give it a try this evening when I get home... will probably work just fine.

For a multiplier you might want to consider a simple full-wave rectifier to raise the pitch up one octave. This might be easier to implement (with your limited time horizon) than to work with a PLL chip.

You may be able to cascade rectifiers to shift up by additional octaves. I've never tried it. After all, to shift up one octave then divide down one octave doesn't give one much more than one would get by simply playing the theremin an octave higher. The full benefit would come from shifts greater than one octave.

Also, if you shift up high enough -- say by four octaves, you could simply run multiple dividers to achieve harmony. The complication of multiple multipliers may exceed the actual benefit. In other words, I'm suggesting that (for starters) you use one multiplier that, in turn, supplies multiple dividers.

Also, try to keep things simple -- particularly with a limited time-horizon. With one to three dividers, you can get some really cool sounds!

Great idea, Gordon. Look forward to read about your progress and to hear the results.

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Gordon Charlton



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PostPosted: Thu Sep 02, 2010 10:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Kevin,

Yup, dividers are great! The thing I love most about the etherwave pro is its bass register - I'd love to have that on my etherwave standard. Also I'm starting to wonder why the humble square wave is so maligned. Maybe it's because it is associated with crappy little speakers and buzzers. They sound pretty good on my amp!

I see the Yusynth divider uses 4017s so I guess I'm on the right track. I imagine all the extra circuitry is to make it sound nicer. Personally I'm happy with the lunetta rough-and-ready approach - at least for a proof of concept device.

Full wave rectification on a square wave? How does that work? I see that with a sine wave in you'd get a sort of epicycloid shaped waveform:

http://www.play-hookey.com/analog/full-wave_rectifier.html

and that a triangle wave would yield a triangle wave, but surely a square wave would yield either a 0% or 100% duty cycle (i.e. a straight line in a mathematically perfect world, or one with a little periodic glitch in the real world)?

(Footnote - I spotted a square to triangle converter on Art Harrison's site:

http://theremin.us/Circuit_Library/converter.htm

I'm thinking that might be interesting after I've got the harmoniser all working to give it a choice of timbres.)


(edited for spelling)

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PostPosted: Thu Sep 02, 2010 10:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Gordon Charlton wrote:
I see the Yusuth divider uses 4017s so I guess I'm on the right track. I imagine all the extra circuitry is to make it sound nicer. Personally I'm happy with the lunetta rough-and-ready approach - at least for a proof of concept device.


The extra input circuitry converts the input signal to a square wave via Schmitt triggers. The output circuitry is simply a driver for the LED and the output signal.

Gordon Charlton wrote:
Full wave rectification on a square wave? How does that work? I see that with a sine wave in you'd get a sort of epicycloid shaped waveform:


Good catch -- you would have to perform this on your theremin's signal.

You could run your square wave through a capacitor to capture a spike for each state change of the square wave.

Of course, there are various techniques to make this all work.

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PostPosted: Thu Sep 02, 2010 1:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Gordon

It's just occurred to me that much of what you want is contained within the "Waveshaper" section of Kevin Godwin's "Picsynth":

http://picsynth.000space.com/schematic.html

This provides sub-octaves, pulse width adjustment, triangle and sawtooth waveforms from your square wave input. Okay, the 'sawtooth' is actually a four-step stairstep function, but it will still provide a richer source of harmonics than will a square or triangle alone (as will the pulse width variation).

Not only will this provide a simple but powerful starting point, Kevin also presents an add-on 4046 circuit that expands the waveforming circuitry considerably.

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Gordon Charlton



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PostPosted: Thu Sep 02, 2010 2:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you Kevin, I understand the Yusynth divider circuit a bit better now, so am slightly less confused. But to compensate I looked at the Wikipedia article on Schmitt triggers and learned that the 4017 already has Schmitt triggers on the inputs. I'm guessing that the transistor trigger is better suited to an audio input - diferent hysteresis points or something.

(Which reminds me of another point. I've had no problems plugging various audio devices into my cacophonator, (headphones, amp, volume loop of my etherwave) but would it be better to condition the output so that it is at line level, whatever that is, rather than at logic level (0-5v?))

Phil - I'll look at the picsynth when I have access to my laptop - I'm on the iPod at the moment while the missus plays Bubble Shooter.


(edited for spelling)

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MirlitronOne



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PostPosted: Thu Sep 02, 2010 4:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Logic level on the Cacophonator is nearly 9V (supply voltage). If it works, don't fix it, but if you're concerned, drop the output to 1V (approximately line level) by breaking the connection between the output capacitor and the 100k resistor, and solder a 1M (megohm) resistor in the gap.
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PostPosted: Thu Sep 02, 2010 5:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK. It works, so I'm not fixing it. Wise words.

(edit - just spotted a line-level-er-izer here, on the same page as the Heterodyne Space Explorer. It appears to be built in to the HSE so it looks like the HSE mixer has live level outputs.)

Why did you have to show me the picsynth? I understood big chunks of it and then browsed around the site and listened to sound samples and now I understand that I have started down a path that could last for decades - adding more and more functionality to a simple little idea until I have a theremin that not only plays chords but can generate every waveform known to mankind, filter them in endless different ways and even flipping well arpeggiate the notes.

Aaaaargh! I must be strong and not think about that until I have achieved my initial goal...

But just to confirm that I grasped the bit you showed me... a sawtooth comes out of the PIC based frequency divider, the first op-amp turns it into a variable width pulse by varying where the upper hysteresis point is (which principle would work just as well with a triangle wave, I presume) and the second op-amp turns it into a triangle wave by some sort of feedback mechanism that I don't really need to understand yet.

OK. Back to the plan. I want to get another little stand alone noise-maker under my belt before I start breadboarding things based on chunks of circuit culled from other circuits. So next week I'll order the bits for a heterodyne space explorer and practice working directly from a circuit diagram rather than a layout. And after that comes a frequency divider, then a multiplier (I really do want to multiply by other than powers of two - I'm decided on that aspect - to make something as basic as a perfect fifth I need to multiply by three and divide by two - pretty much essential to a harmonizer.) And finally put all the bits together.

It all sounds quite simple when I say it quickly.

(Oh, and of course I meant cycloid, not epicycloid. What ever was I thinking?)

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PostPosted: Fri Sep 03, 2010 7:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Just a quick update --

The Yusynth dividers (based on the 4017 chip and discreet transistors) works through the entire audio frequency spectrum. I was getting a lot of cool sounds by changing the divisor values.

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Gordon Charlton



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PostPosted: Fri Sep 03, 2010 12:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's great news, Kevin. Thank you for doing that experiment. Smile
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PostPosted: Fri Sep 03, 2010 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh yeah, you're on the long road now, Gordon. But fear not, because your immediate goal - a chord-playing theremin - is on the route you are taking anyway, so long term aims are not going to distract you from the short-term goal.

However, I would think twice about building the heterodyne space explorer because it's not that different from the Cacophonator. It has two fewer oscillators, and so lacks the rhythmic effects that the latter offers. It has an option of diode, rather than resistor mixing; I modified my Cacophonator with that option, and didn't much like the results (although we two have different thresholds of "nasty" in sound, I admit!). Apart from that, it has the option to vary the level of each oscillator in the mix, but...

Don't let me stop you - in fact, you know I'll help as much as I can if requested - but I have my doubts that you'll get much out of the HSE. I would think more in terms of something to modify your theremin tone, such as a square wave shaper (immediate access to higher harmonics), followed by a divider (rattle those windows!). If you think you want more circuit-building experience first, how about an Atari Punk Console? Weird sounds, but eminently playable.

Just my two euros worth... Wink

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PostPosted: Fri Sep 03, 2010 5:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

MirlitronOne wrote:
Don't let me stop you

Haha. As if.

The similarity is part of the appeal. Especially as someone talked me into getting a spare 40106 that is now sitting forlornly on a shelf failing to fulfil its destiny.

But don't fret. I have a cunning plan - the reason I intend to space-wire the circuit is not only so that it will look wikkid kool in its translucent blue box but also so that I can avoid trimming the legs on the components for ease of recycling if I'm disappointed with the sound.

Anyroad, I just spent an evening filling my basket at Rapid (complete with a modern art sculpture of a little robot with crocodile clip hands and a magnifying glass head. I will hug him and stroke him and cuddle him and call him George) so there's no turning back now.

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PostPosted: Sat Sep 04, 2010 3:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Tee hee, point taken. Wink

I only got you to buy that spare 40106 to start you on the way to your Weird Sound Generator or Lunetta, you know...

Please remember that you must connect the two unused gate inputs to earth!

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PostPosted: Sun Sep 05, 2010 7:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Good point, Phil. Thanks for mentioning it. 

I've been researching chords a bit as background to this project. Gosh, they're complicated. 

One interesting page I found is here. It's a list of "the twelve four-note chord forms used in popular music".

That's not a phrase I can say out loud without sounding sarcastic (emphasis on the and popular), but it does suggest a reasonable selection of 12 presets, if I wanted to add one.

It also highlights the problem of the Major Seventh. I can't dial up a Just Major Seventh (15/8) on one multiplier/divider pair. But I can make it as the difference of two pairs: 5/2 and 8/5. Now I need to figure out if I can do that whilst generating other notes in the popular chords. Sigh. Time to oil some rusty brain cogs. It's been a while since I did vulgar fractions.

One thing is clear though - shifting the overall pitch of the chord at the same time is out of the question. So a separate octave(s) down unit preceding the harmonizer is certainly a good idea, and a worthwhile sub-goal before building the full harmonizer. You were quite right to suggest it, Kevin.

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PostPosted: Mon Sep 06, 2010 3:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Re: the Major 7th problem. It can't be done for three of the chords. Sad

(It boils down to the fact that 8 and 15 are mutually prime - as are 7 and 15 and also 5 and 8 so there's no way to simplify the 15/8 whilst generating 8/5 or 7/5 with a ten stage counter.)

Hmm.

Ten is such an arbitrary number.

15 isn't. it's the largest number representable as 4 bits.

Idea

I've got a second hand copy of Modern CMOS Circuits Manual by R.M. Marston on its way to me. (Not in good condition, but cheap. The good condition ones are £22 on Amazon. Ugh.) Chapter 9 is all about counters and dividers. And there are several different 4-bit binary counters in the 4000 range.

I think I'll have to read chapter 9 first. Smile

Then I will invent the OCD Light Switch. (It only works if you turn the switch on and off fifteen times. Wink)

Note to self - Binary coded hex switch with extended shaft and through hole mounting here.

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MirlitronOne



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PostPosted: Mon Sep 06, 2010 1:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's an excellent book, well worth £22. I know, because I found my copy earlier this year. (I paid 50p for it.)
Twisted Evil Twisted Evil Twisted Evil Twisted Evil Twisted Evil

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Gordon Charlton



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PostPosted: Mon Sep 06, 2010 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

I was feeling good about getting the last one on Amazon for less than a fiver.

Anyway, hopefully it'll answer a bunch of questions that are buzzing around my head. Such as: if inputs always have to be connected to something, how does that work with a spst switch? (give it a permanent connexion to ground with a resistor in the path for when the switch is off?), if binary counters only switch on rising voltages, does count-to-three mean divide-by-six et cetera? if it does, will a count-to-three inside a PLL mean multiply-by-six so this doubling effect cancels out when a multiplier is followed by a divider? what if I try to divide by zero? will I create a sonic singularity?

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