On 26 Feb 2004 at 8:05, Spehro Pefhany wrote:

> At 12:24 AM 2/27/2004 +1300, you wrote:
>
>
> >Hi Ed,
> >
> >That was just a circuit I had lying around, which is admittedly more
> >complicated than what is necessary on hte Tx side and too simple on
> >hte Rx side.
> >
> >Check out the attached circuit for something simpler/better. It shows
> >interfacing of logic levels between a 3.3V device and a 5V device, in
> >both directions.
> >
> >Note that the diode drop determines the logic 0 level, so schottky
> >diodes would be best.
>
> This isn't that great a circuit. The high level at the PIC input is
> 3.3V+Vf, maybe 3.6V with a Schottky. It needs to be a minimum of 4V +
> noise margin on ST inputs such as RxD on the PIC16F628A to be
> guaranteed to work.
>
> Your original circuit is much better, especially with the addition of
> a 20K to ground on the GPS RxD input. It can be made with 3 parts- a
> dual NPN transistor, a 4-resistor 10K network and a 20K.

You are absolutely right, thanks. Guess it was too late when I drew up that
circuit last night.

Cheers, Brent.

--
Brent Brown, Electronic Design Solutions
16 English Street, Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/txt: 025 334 069
eMail:  brent.brown@clear.net.nz

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