[sdiy] VCO waveform logic selection

[Magnus Danielson]

From: "Mattias Rickardsson" <mr at analogue.org>
Subject: Re: [sdiy] VCO waveform logic selection
Date: Tue, 11 Sep 2007 16:20:15 +0200
Message-ID: <1f4a82040709110720v6e801c74m252f5af24ded55c6 at mail.gmail.com>

Mattias,

> How about doing the Prophet~5 trick and putting the 4051 on the other
> side of the resistor, namely at an OPamp input where it's at virtual
> ground potential? This will let it eat any signal level, and will also
> prevent distortions caused by the 4051 on-resistance varying with
> input voltage.
> 
> If I've understood things correctly. :-)

I think you got it pretty much nailed. This is a better method of applying
them. However, if there is leakage through the 4051, then it is pretty much
undampend. A trick there is to have load-resistors on the 4051 inputs, so that
there is at least some damping, but they are mostly disabled for the enabled
input as it sits into the virtual input.

Cheers,
Magnus

> /mr
> 
> 
> On 11/09/2007, Michael Ruberto <frankentron at hotmail.com> wrote:
> > JB
> >
> > You could try a better device for starters. Get samples of the ADG333 from
> > Analog Devices. They handle signal levels up to the supply rails and have
> > 2.4V HI level digital inputs.
> > http://www.analog.com/en/prod/0%2C2877%2CADG333A%2C00.html
> >
> > M. A. Ruberto
> >
> >
> > >From: jbv <jbv.silences at club-internet.fr>
> > >To: synth-diy at dropmix.xs4all.nl
> > >Subject: [sdiy] VCO waveform logic selection
> > >Date: Tue, 11 Sep 2007 11:12:53 +0200
> > >
> > >Hi guys,
> > >
> > >Let's say I have a vco module that outputs various waveforms at +-5V.
> > >And I want to digitally select 1 of these ouputs to send it to the input
> > >
> > >of another module. What is the best way to proceed ?
> > >
> > >would some analog mux like the 4051 do, if its power supply is set
> > >to +-7.5V ? If yes, how to handle logic selection signals, especially
> > >if they're generated by 3V logic uC ?
> > >
> > >Thanks in advance,
> > >JB
> > >
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