At 12:09 AM 8/21/2004 +0100, you wrote:
>On Fri, 20 Aug 2004 09:27:54 +0100, you wrote:
>
> >>Any suggestions/recommendations for opto-coupling a
> >>DC or low frequency signal (10s of Hz) to the AN pins
> >>for measurement ? Maybe V-F -> F-V for example ?
> >>Pointers to a proven design would be absolutely spiffing
> >
> >Look at the Agilent HCPL-7800 (available through RS or farnell, cannot
> >remember which I got from). It is designed for isolated motor current
> >measurements, so the input side will handle only about 300mV, so you may
> >need to scale that, but it does have a small amount of gain across the
> >isolation. Requires 5v supply on both sides.
>
>  I'd use a PIC12F675 on the remote side as an intelligent ADC, sampling
> the data and squirting the
>data (e.g. as async data)  through an optoisolator.
>The fact that you can use a dirt-cheap optoisolator for the sort of data
>rates you need will
>probably more than offset the cost of the 12F675 compared to using any
>sort of fancy analog
>isolator.

Yup. Think of the 12F675 as an intelligent ADC. You get unadjusted
accuracy as good as the isolated power supply, pretty much, without the
issues associated with trimpots etc.

I also like the idea of cycling the power as the conversion-request signal.
Only one opto required, and a hardware serial port could be used on the
other side. Especially nice on chips that have a couple of those.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics