On Mon, 8 Mar 2010 08:30:33 +0200, "Marechiare" said:
> > I'm looking for a single supply voltage to frequency
> > converter.
> ...
> > 10KHz is fine.
> > US$ 5 for all the parts including an optoisolator.
> > Size isn't a problem but fewer parts is always better.
> > Square wave is what I need.
> > 3% accuracy 0 to 50 C.
> 
> Perhaps PIC10F, a capacitor and a few resistors could do the job.
> 
> - let the voltage input to charge the capacitor;
> 
> - when the PIC's comparator detects the certain voltage is reached on
> the capacitor - the PIC's pin would be changed from "input" to
> "output" and the capacitor would be discharged;
> 
> - the pin would get back to the "input" state waiting to detect the
> voltage on the capacitor;
> 
> The higher the input voltage - the higher frequency of the process.
> With the proper parts it should work for "3% accuracy 0 to 50 C", I
> believe.

Yes, a small PIC can be an excellent VFC, mimicing the functions of a
dedicated VFC chip almost exactly. But now I think I want to use one
with an A/D converter and bandgap reference, because then I won't be
dependent on the tolerance of a capacitor, which will either be very
expensive for a 1 or 2 percent part, or else need to add a trimpot and
an extra test step to calibrate it.

I am thinking along the lines of a 16HV616, it has a shunt regulator VSS
to VDD (this is a self-powered isolated battery monitor) interrupts and
a CCP module so I can generate the frequency reliably.

Cheerful regards,

Bob


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