[sdiy] Expo converters, lin log etc.

[Scott Gravenhorst]

Karl Ekdahl <elektrodwarf at yahoo.se> wrote:
>Hi list
>
>Basically what i was doing was toying with a
>multivibrator, it seems however that it's perhaps not
>suitable for a VCO..
>
>Karl

C'mon Karl, a schematic, please...  (c;

If I'm not mistaken, isn't the 555 timer circuit used in the FatMan
VCOs a multivibrator?  It's forced to be linear by using a current
source to charge the cap instead of a resistor.  So I think that a
multivibrator can be used if it's cap charge circuit is designed
properly.  

Or did I mess up on what a multivibrator is ??


>
>
>--- Magnus Danielson <cfmd at bredband.net> skrev:
>
>> From: Karl Ekdahl <elektrodwarf at yahoo.se>
>> Subject: SV: Re: SV: Re: SV: Re: SV: Re: [sdiy] Expo
>> converters, lin log etc.
>> Date: Sun, 4 Feb 2007 04:09:23 +0100 (CET)
>> Message-ID:
>> <797372.94778.qm at web26213.mail.ukl.yahoo.com>
>> 
>> > Hi All, 
>> 
>> Hi Karl,
>> 
>> > I'm a little slow responding (to much work) but
>> thanks
>> > a lot for your input!
>> > 
>> > I've got no schematic for this circuit as i pretty
>> > much just tossed together something to try and
>> develop
>> > my own VCO. I just want to learn how to do it
>> myself
>> > from scratch, all the figures people have listed
>> makes
>> > me now know a little bit more of what look for.
>> 
>> Well, then you need to reverse engineer it so we
>> have a schematic to comment
>> on!
>> 
>> > I was thinking of just hopping on to another
>> circuit
>> > if this is a dead cause, but according to magnus's
>> > response below there seems to still be some hope?
>> 
>> We will see.
>> 
>> > > But as it has been noticed, if you remove the 0V
>> > > hertz count from the rest
>> > > measures, what you are left with is indeed
>> > > exponential. This should be the
>> > > result of a constant DC current pulling the
>> > > oscillator at a constant rate,
>> > > onto which the exponential current is added. I
>> > > haven't seen the schematic of
>> > > what you attempt to run, but I think you still
>> > > should be able to improve things
>> > > by propper debugging now that you know there is
>> a
>> > > current-pull somewhere which
>> > > is significant.
>> > > 
>> > > You might learn something, don't miss out on the
>> > > oppertunity! :)
>> > 
>> > That's exactly what i don't want to, so perhaps
>> i'll
>> > just wire up the old circuit again and see if i
>> can
>> > figure something out.
>> 
>> What type of oscilltor is you attempting to build?
>> Exponential or linear?
>> 
>> What is your inspiration?
>> 
>> Cheers,
>> Magnus
>> 
>
>
>
>	
>	
>		
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-- ScottG

---------------------------------------------------------
-- Scott Gravenhorst
-- Xilinx Spartan-3E Based Music Synthesizers
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/