[sdiy] converting a 10v p to p to a 0-5 volt signal

[Adam Schabtach]

I've considered that option (and yes, one of the few textbooks I retained
from my college years has a selection of relevant circuits), but it's always
seemed somewhat more complex than it needs to be. OTOH one quad op-amp and
four diodes is obviously not very complex, so I can't really say what I was
thinking at the time. Maybe dropping a diode into the feedback loop of the
input-scaling circuit would do the trick. (Does the superposition rule apply
here?)

Clipping at 5.1V isn't really good enough, though. The Absolute Maximum
Ratings for the ATmega microcontrollers I use specify an upper limit of
Vcc+0.5V on any pin.

--Adam 

> -----Original Message-----
> From: David G. Dixon [mailto:dixon at interchange.ubc.ca] 
> Sent: Wednesday, May 20, 2009 12:40 PM
> To: lists at studionebula.com; synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] converting a 10v p to p to a 0-5 volt signal
> 
> To clip to ground without the diode drop, you should use an 
> active rectifier.  This is basically a diode in the feedback 
> loop of an opamp.  Any decent book on opamps will have a 
> selection of such circuits with different attributes (half or 
> full-wave rectification, different input impedances, virtual 
> ground summing nodes, etc, etc).  I believe that the addition 
> of a 5.1V zener in the loop would clip on the high end.  That 
> may be all you need to do.  Perhaps one of the gurus could 
> weigh in on this...?
>  
> > Aside from range scaling, I'm still looking for a good protection 
> > circuit for microcontroller inputs. I want hard clipping at 
> 0V and 5V 
> > to protect the micro. I've seen various solutions described on this 
> > list, but when I put them into SPICE I have always found some flaw, 
> > such as the lower limit actually being one diode-voltage-drop below 
> > zero rather than zero. I'd be very happy if I could find some nice 
> > solution to this problem so that my micro-based modules can protect 
> > themselves rather than having to depend upon my poor memory 
> to avoid 
> > being subjected to unacceptable voltage ranges. :-
> > )
> > 
> > Or, putting it another way: converting 10Vp-p to 0-5V with 
> op-amps is 
> > a fine solution, but as soon as you add two 10Vp-p signals together 
> > (e.g. mixing two LFOs) the input range can easily exceed 10Vp-p and 
> > hence the output range will also exceed 0-5V.
> > 
> > --Adam
> > 
> > > -----Original Message-----
> > > From: synth-diy-bounces at dropmix.xs4all.nl
> > > [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jason 
> > > Proctor
> > > Sent: Tuesday, May 19, 2009 6:50 PM
> > > To: synth-diy at dropmix.xs4all.nl
> > > Subject: Re: [sdiy] converting a 10v p to p to a 0-5 volt signal
> > >
> > > i did exactly this for my Arduino module. it bidirectionally 
> > > interfaces a +/-5v signal to the micro's 0-5v range.
> > >
> > > turned out to be pretty easy - on the way in, chop the signal in 
> > > half, and bias with +2.5v. then reinvert. on the way out, do the 
> > > opposite. 1 dual opamp each way.
> > >
> > > lmk if you want the details.
> > >
> > > (i should also thank Tom Wiltshire here for his help 
> getting me off 
> > > the ground with this stuff.)
> > >
> > >
> > > >tonight i was looking at my scope
> > > >
> > > >Checking the input into a circuit that was only able to take
> > > 0-5 volts
> > > >
> > > >Sure enough, the signal was between 0 and 5 but the sawtooth
> > > was clipped.
> > > >
> > > >So i am looking for a input block that can take either 
> 5vp to p or 
> > > >10v p to p (or any synth signal) and spit it out as a 0-5 signal 
> > > >without squaring the top.
> > > >
> > > >
> > > >anyone know of a good circuit for this?
> > > >
> > > >thanks
> > > >
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