[sdiy] VCO waveform logic selection

[harrybissell at wowway.com]

Yes you understood correctly. The 4051 actually has some resistance which is
in series with the input resistor, forming a voltage divider. Maybe 100K /
100ohms ???

They also bias the Vss to -0.7V with a diode and resistor to the negative
supply, allowing bipolar signals to be processed without distortion (the
voltage across the analog switch is REALLY tiny

H^) harry



On Tue, 11 Sep 2007 16:20:15 +0200, Mattias Rickardsson wrote
> 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. :-)
> 
> /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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Harry Bissell & Nora Abdullah 4eva