I don't think it will matter in your case, but don't forget that
adding the MOSFET to isolate the data line will invert the signal.

RP

On 25/01/07, Rolf <learr@rogers.com> wrote:
> Shoot, that's so logical.
>
> I can put the TX on it's own diode from the battery, and I can use a
> MOSFET to control the Data Line. This will provide 3.6V safety at all
> times. I will have to "reverse" the sense of the data transmission, 1
> now means 0.
>
> Thanks, that makes a big difference. I can put a second Cap for the TX
> in as well, It will have to be based on the "real" ground, not the
> analog ground. I will ensure that the caps are placed near the IC's, I
> though I had placed it near the PIC, but I hadn't.
>
> Thanks again. See, updated schematic attached.... pretty picture. It's
> more obvious now seeing the isolation through the two MOSFETS.
>
> Rolf
>
> Richard Prosser wrote:
> > Just on a quick review.
> > It might pay to add a bit more decoupling as close to the 2 ICs as possible.
> > As far as the programming voltage is concerned - could you connect the
> > TX chip to the battery via a separate diode. This would prevent it
> > being powered by more than the battery voltage less a diode drop.
> > There may be an opportunity for 5V to be applied to an input however.
> > e.g. the data Input?. This may need protection using a series R and a
> > diode or zener.
> >
> > RP
> >
> >
>
>
>
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