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 Forum index » DIY Hardware and Software » Developers' Corner
Ultra simple saw LFO?
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Kenneth



Joined: Apr 16, 2009
Posts: 43
Location: Stockholm, Sweden
PostPosted: Mon May 11, 2009 7:42 am    Post subject: Ultra simple saw LFO? Reply with quote  Mark this post and the followings unread
Will this work?

Code:

Shematic:
           ____
5 volt ---|NAND|________.     
       .--|gate|        |---(square)
       |   __________   |
       |--|portamento|--´
       |
       ´---------------------(saw)


As I understand there is a difference between the voltages where the output from the NAND goes from 0 to 1 and from where it goes from 1 to 0. The idea is to use that difference to create a saw LFO (and get a square for free but I need the saw).

The portamento is a knob and a cap that creates a delay in the change of voltage, if this works, what values would i need to get "normal" LFO rates? (like 0.5 to 30 hz or something)
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blue hell
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Joined: Apr 03, 2004
Posts: 24391
Location: The Netherlands, Enschede
Audio files: 296
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PostPosted: Mon May 11, 2009 9:32 am    Post subject: Re: Ultra simple saw LFO? Reply with quote  Mark this post and the followings unread
Kenneth wrote:
As I understand there is a difference between the voltages where the output from the NAND goes from 0 to 1 and from where it goes from 1 to 0.


There would be when you'd use a hysteresis port like the cd4093, or alternatively just use an inverter with schitt trigger on it's input, like the cd40106.

For non schmitt triggered inputs there is not really much difference in the switching levels for upgoing or downgoing edges, it would oscillate on a very high frequency.

Anyway, you just re-invented the relaxation oscillator Cool

As for the timing (in seconds), a rough indication would be the product of R (in Ohms) and C (in Farads), just experiment a bit ... however there will be some issues for very low frequencies, and the wave form wll not be exactly like you'd expect it to be ... but it would work Exclamation
_________________
Jan
also .. could someone please turn down the thermostat a bit.
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Kenneth



Joined: Apr 16, 2009
Posts: 43
Location: Stockholm, Sweden
PostPosted: Mon May 11, 2009 11:11 am    Post subject: Reply with quote  Mark this post and the followings unread
OK, thank's a lot Smile

I just happen to found a dual NAND in an old VCR and I thought it may be useful. I'm trying to put my DIY parts together from scrap parts only, that VCR had two cups full of nice parts...

Well have to look at some old computer cards I got laying around then, to find more useful stuff than my NAND and then go for the experiments Cool
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