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

[harrybissell]

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  I think the 4d is obsolete now...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
> >