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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
How should I start down this path?
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Uncle Krunkus
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PostPosted: Fri Jun 01, 2012 2:16 am    Post subject: How should I start down this path?
Subject description: Any stuff I should think about.
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I've just done a big cleanup of "The Lab" and have realised that I have about 54 different kinds of 74LSXX chips. Shocked
I would have been the first person to say stick with CMOS on a Lunetta, but I'm thinking the 5V monster of 74XXXX technology could be a viable beast. I've looked at all the descriptions, and they seem to cover all the same functions as CMOS stuff. Cool
Any considerations from those who have done Lunettas would be greatly appreciated in this planning stage.

"This is another fine mess you've gotten us into Ollie!" Laughing

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PostPosted: Fri Jun 01, 2012 3:04 am    Post subject: Re: How should I start down this path?
Subject description: Any stuff I should think about.
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Uncle Krunkus wrote:
I'm thinking the 5V monster of 74XXXX technology could be a viable beast.

GO FOR IT! It can be done and there's no sense is letting good chips go to waste Wink
The main consideration is that the input impedance is considerably lower in TTL, thus standard oscillators made with a 7414 require much lower resistance in the feedback path and much higher capacitance than CMOS equivalents. The maximum resistance which I found to work in 7414 oscillators was 2.2k. The output waveform have uneven duty cycle.
There are also minimum resistances that should be observed in making such an oscillator, check the datasheets to see how much current they can output without damage and add a limiting resistor of suitable value in the feedback path (in series with the pot, if a pot is used that is). I would say, probably about 330ohms is a good estimate.
Some TTL chips have open collectors or emitters on the outputs and so require a pull up or pull down resistor in all situations (again, another datasheet hunting trip is in order).
On the positive side they are significantly less susceptible to static discharge Very Happy

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Uncle Krunkus
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PostPosted: Fri Jun 01, 2012 4:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Well,
to be honest, I think modern CMOS are virtually immune to all but the most buffoon like of buffoonicans. I haven't zapped a CMOS chip in 30 years of DIY electronics. Although some very learned people believe that you can reduce their lifespan with static, quite apart from the potential for complete cactusness.
I'm yet to see it.
But my main concern is interfacing problems.
Thanks for the tips Jingle.
What module does everybody covet?
Where am I going with this project?
What can I expect when I unleash the hords of demondem upon the earth and all it purveys,....hmm,.....hmmmm.
Anyway,......
Tell me things people!?!

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Draal



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PostPosted: Fri Jun 01, 2012 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

I dig multiplexors aka channel selectors with ABC controllers. Feed the inputs with a divider for your "octaves", and use anything from shift registers to more oscillators for the ABC controllers and you are makin' tunes.

I am building another lunetta (4000 series): a mini compared to my big one. It uses 4 oscillators each with a switch to change cap values, a 4052 multiplexor (I have a crap load to get rid of), a 4094 shift register, a simple passive mixer ala slacker, and my not so secret weapon, a PPL chip (cd4046) set up as pitch tracker. Turns even the most boring blips into something rockin'.

I don't need an R2R ladder or vco because the pitch tracker is quite audible and when I use the multiplexor and divider method, I run my divider at audio levels obviously so the divisions are actually heard. ABC select what order to play the divisions. Of course, there's absolutely nothing wrong using r2r ladders and vco's but I like to keep things as simple as possible. Keeps it fun Very Happy .

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JingleJoe



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PostPosted: Fri Jun 01, 2012 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Draal wrote:
Of course, there's absolutely nothing wrong using r2r ladders and vco's but I like to keep things as simple as possible. Keeps it fun Very Happy .

Also the digital control over frequency division is often better than R2R ladder control for un-exponentiated VCOs. I often find that one end of the R2R ladder has hardly any variation in pitch while the other has too much.

I've zapped a few chips in the past with static, I presume static anyway; because I have long hair and it was winter at the time.

What do you mean by interfacing problems anyways? Human interfacing or interfacing between devices? For the organics just add some switches, some dials and a patch bay and Bobs your uncle Smile
As far as connecting in other signals, just make sure they are square waves and within the voltage limits of your ICs then you should be fine Wink

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richardc64



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PostPosted: Fri Jun 01, 2012 9:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, go for it, but keep a couple of things in mind.

TTL inputs are difficult to pull down with any resistance greater than 470 ohms or so. 1k would be unreliable. Unterminated inputs will "float" high, but that shouldn't be relied upon, either. I wouldn't use a pull up greater than 22k. the upshot of this is ENables/DISables will need to be active-low. And although diode Mickey Mouse logic can be added to inputs, it would have to be the AND configuration, diodes "pointing" away from the inputs.

LS TTL output voltages aren't as consistent as CMOS: typically 3.4V but can be as low as 2.7V. This will make building R/2R ladders -- or even binary weighted summing -- with any precision difficult. But Lunettas aren't about precision, right?

JingleJoe wrote:
The maximum resistance which I found to work in 7414 oscillators was 2.2k. The output waveform have uneven duty cycle.
Although duty cycle asymmetry is not as severe with CMOS schmitt oscillators, it does exist. Compare what you get with a 10k feedback resistor vs 100k or 1M.

Overall, I think a mix of CMOS inputs and outputs with a TTL "core" would be a viable architecture.

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PostPosted: Mon Jun 04, 2012 1:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Very interested in what you come up with Unkle K!

There are lots of fun paths to explore:

--Interesting CV generation with r2r ladders, etc.
--Frequency divisions driven by interesting data generation with the shift registers, mux,etc.
--Awesome step sequencers
--Other, etc.

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Uncle Krunkus
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PostPosted: Fri Jun 08, 2012 6:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's a shot of the 74xxXX cab.
I just finished working out what I had and labeling it all in preparation for "doin' the 74 squeegee"!


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PostPosted: Fri Jun 08, 2012 7:14 am    Post subject: Reply with quote  Mark this post and the followings unread

As a slightly relevant tangent: where do you chaps find those nice chests of tiny drawers?
What I really need is one them with drawers that are the length of the width of a tape of resistors Smile and only about an inch wide. Then I'd be able to fit a good bundle of components in each one and a few ICs.

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PostPosted: Fri Jun 08, 2012 9:19 am    Post subject: Reply with quote  Mark this post and the followings unread

I actually like these better.
They're all metal, with plastic drawers. Got em for nothin. Un-Believable. Smile
The resistor drawers (left hand side) are the perfect width for a bandolier of resistors. I've got three values in each drawer. Trying to use up my carbons. Wink


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PostPosted: Fri Jun 08, 2012 12:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
I actually like these better.
They're all metal, with plastic drawers.

Cor blimey they are nicer Very Happy
Quote:

Got em for nothin. Un-Believable. Smile

Where!? I've scavenged from a closing down electronics shop or two but never found any chests of drawers Sad

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PostPosted: Fri Jun 08, 2012 12:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Most of my "original" Lunetta stuff from the 70s is RTL, so I'd say going to TTL is a big step forward. Smile

You will find things work a little differently from CMOS, but that gives it a special character. The main difference is power consumption and the threshold voltage of TTL is not symmetrical like in CMOS. In CMOS you can almost always drop an LED and a resistor on an output without too much trouble, but in TTL, it may have a more serious effect on the circuit. You may need to add buffers to drive the lights. Experimentation is, as always, the way to make progress.

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Uncle Krunkus
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PostPosted: Fri Jun 08, 2012 5:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

JingleJoe wrote:
Where!? I've scavenged from a closing down electronics shop or two but never found any chests of drawers Sad


Got it in one.
Dick Smith electronics, Kempsey. Just happened to be walking past as they were clearing out the shop. I got all the components they had for $200 and then they through in the cabinets they were all sitting in! Heaps easier to just let me "get rid of them".

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PostPosted: Sat Jun 09, 2012 5:33 am    Post subject: Reply with quote  Mark this post and the followings unread

I'll keep an eye out, but there's only about two electronic component shops in Liverpool now Rolling Eyes
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PostPosted: Sat Jun 09, 2012 12:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

JingleJoe wrote:
As a slightly relevant tangent: where do you chaps find those nice chests of tiny drawers?
What I really need is one them with drawers that are the length of the width of a tape of resistors Smile and only about an inch wide. Then I'd be able to fit a good bundle of components in each one and a few ICs.


I've found mine at hardware stores, places that sell power tools and stuff for workshops usually have them. Machinists and the like may have them for assorted hardware components. I've also found them with components like various screws and fasteners as a pack at places like harbor freight (USA).
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