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.

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: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads