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 Forum index » DIY Hardware and Software
Simple LED flasher circuit for vactrol pitch LFO?
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gmeredith



Joined: Jun 28, 2006
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Location: Tasmania, Australia
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PostPosted: Wed Jun 28, 2006 5:25 pm    Post subject: Simple LED flasher circuit for vactrol pitch LFO? Reply with quote  Mark this post and the followings unread

Hi,
I'm a newbie looking to add a pitch vibrato to my bent Casio SK1 via a vactrol resistor. I need a simple LED flasher circuit that can flash from 1 flash/second up to about 20/second. All the 555 circuits i've seen only seem to flash slow (up to 2/second). Does any one know of one?

Thanks for your help, great forum

Cheers, Graham
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Scott Stites
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PostPosted: Wed Jun 28, 2006 10:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Graham,

You should be able to get a cap value on a 555 circuit to get a faster flash rate on a 555 (in this case, if you're running off of battery, I'd suggest a 7555, which has a mere fraction of the current draw a 555 has).

If that doesn't do the trick, a simple op amp LFO driving the LED might work, but I suck at single supply circuits - the Uncle K-man might have some good suggestions. Plus he might have a better grip on any coriolis related issues for down under Very Happy

Cheerio,
Scott
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gmeredith



Joined: Jun 28, 2006
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PostPosted: Wed Jun 28, 2006 10:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I am running it off batteries - the Casio runs off 5 "AA" batteries (7.5V total), so current draw is an important factor here - I'll check out the 7555. Is it a direct replacement for the 555, or does it have different pin-outs?

Thanks for the great advice Very Happy

Cheers, Graham
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dnny



Joined: Mar 12, 2005
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PostPosted: Thu Jun 29, 2006 1:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Graham welcome to electro-music.com forum

have you tried 555 timer lite?. freeware that calculates the component values for desired timers using 555 and 556.

here is example whit 6volts (use only 4 AA batteries) and 20Hz (20times/second)
Posted Image, might have been reduced in size. Click Image to view fullscreen.
you can tweak the values until you get what you wanted.

should this topic be moved to our circuit bending sub-forum ?
opinions?

daniel

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Mikmo



Joined: Dec 01, 2005
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PostPosted: Thu Jun 29, 2006 4:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Go to my website here:

http://www.mikmo.dk/cblfo.html

There's a 555 based LFO, compleate with VERO board and real PCB layout.

To get the timing you want just experiment with the potentiometer value and the timing capacitor.

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gmeredith



Joined: Jun 28, 2006
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PostPosted: Thu Jun 29, 2006 3:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks heaps, guys - looks like the thing I'm after! Thanks Daniel for the link and also the example 20hz - that will get me off to a good start. Thanks Mikmo for your circuit, I think I'll go with it!

Cheers and thanks, Graham
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Scott Stites
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PostPosted: Fri Jun 30, 2006 10:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Don't forget to try a 7555 in there - I've become quite a believer in them. If you're using a battery, the 7555 will not suck it dry. They're also much, much better about not putting garbage on the supply lines. It's pin for pin to a regular 555.

Cheers,
Scott
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gmeredith



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PostPosted: Sun Jul 02, 2006 5:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Scott,
Just finished building the circuit, I got a 7555 as you suggested, it's working really great!!

Just for those wanting a similar thing to me, if you look at the screenshot that Daniel kindly provided above, he showed an example 555 circuit with some values for R1, R2 and C1, to give an oscillation value of 20Hz.

I used the program to fiddle some more values, and came up with:

For a LFO range of 0.3 - 30Hz (an ideal range for your standard synth LFO) the values are:

R1 = 1k
VR2 = 500k
R2a = 4.7K
R3 = 4.7k
C1 = 4.7uF

See the attachment schematic - (a modified Mikmo circuit)

These values give a duty cycle of the LED of about 50% over the entire 0.3 - 30Hz range, which is also important for a synth LFO.


Cheers, Graham


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