[sdiy] Dual power supply solution? - Kits vs 2600

[James Patchell]

You can add me to that group...I make all of my modules independent of the 
power supply.  And actually...a good voltage reference is actually very 
inexpensive.

I use the LM4041-ADJ in a TO92 package...from Digikey these only cost about 
52 cents in 100's (I buy them 100 at a time...I use lots of them).  If I 
need the reference to be precisly set...then I need to add about $1.50 for 
a multi turn trimpot....in general however...I find these little beasties 
work very well....they really don't add much to the cost (The PC board 
itself is generally most of the cost of the module)...and the performance 
increase you get makes them well worth the effort.

         -Jim

At 11:52 PM 6/14/2005 -0400, harrybissell wrote:
>A flip side of Vref changing with the supply voltage is that the
>frequency changes with supply voltage.
>
>If you use a stable reference for the ramp AND the bias for the
>triangle wave generation, you could have wave shape symmetry
>independant of supply voltage.  The ramp would always be the same amplitude.
>Frequency would not be affected...
>
>It still comes down to... do you trust the rails ???
>
>Some of the voltage reference components are not that easy to get in
>'onesies'.. so for an entry level system it might be wise to NOT use 'exotic'
>parts.  I'd sooner buy the voltage references and have to calibrate once every
>few years.
>
>Tom and I were discussing the VCO4d offlist.  I think the 4d is obsolete 
>now...
>
>and the 4e addressed some of the problems of the 4d.  I have not tried the
>3500 series.  I have to check out the tri wave generation... it looks a lot
>simpler than the 4d
>
>Am I wrong, or is there still a pull up resistor missing on the LM393
>comparator
>to get a fast rising positive signal ?  I used a pull up to 'ground' because
>the LM393
>is referenced to the negative supply, and I did not want +/-15V output levels.
>
>Either way, no one is all right, or wrong.  Engineering is a series of
>trade-offs. Some
>folks like Ian and myself will go the more expensive (and maybe larger PCB)
>route.
>Tom is meeting the lower cost market segment... maybe all by himself.  I don't
>provide 'kits' so a few extra components are no big deal.  If I had to buy you
>ALL
>a few voltage references, I might reconsider.
>
>H^) harry
>
>tomg wrote:
>
> > Actually a VRef in a VCO4 would screw it up for use at different supply
> > voltages. Reset is at 1/2 the supply. This changes with the supply voltage
> > if you use a opamp divider. A VRef wouldn't allow for that unless you
> > wanted to trim for each oscillator. The vco3 has no dependant tri output
> > so it wouldn't matter.  I blanket statements that this or that is absolutly
> > better
> > is a looser. It some cases it may be true but not always.
> >
> > Regards
> > Tom
> >
> > > The idea that this would multiply the cost of a system by a factor of ten
> > > or whatever is ... well ... "childish".
> > >
> > > >In modular systmes with mix 'n match components... one
> > > >designer (someone else) may FVCK your design because
> > > >they piss in the swimming pool (power rails) and you
> > > >did not equip yourself with goggles.
> > >
> > > And, additionally, a designer may choose to design modules that can
> > operate
> > > at different supply voltages.  This could actually increase one's market.
> > >
> > >    Ian
> > >

         -Jim
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