Sorry to resurrect this thread, but I haven't had a chance to deal with this until now.

Basically, if I am using a 3.3v power source for the Vcc on the serial device, I really only need one 4.7K resistor between the 5V Tx and the 3.3V Rx, right? That is, if a 3.3V Tx registers on the 5V Rx like it should.

On 3/30/07, Dave Hylands <> wrote:
Hi Chris,

On 3/29/07, Chris Evans <> wrote:
> I want to connect a 3.3v serial device (TTL) to the roboaudio. Can I simply
> connect Vcc to a 3.3v source, and Rx and Tx to the 5v STUART? Will this fry
> my device?

Vcc is a 5v source, so you definitely don't want to connect it to a 3.3v source.

The real question is whether your 3.3v serial device can handle 5v on
its Rx line (because that's what the roboaudiostix generates).

The roboaudiostix should treat a 3.3v signal on its Rx line as a logic high.

> I'm trying to avoid any converters in between, but I don't see any usable
> serial devices that aren't converted to 5v on the roboaudio.

This page shows an i2c voltage converter that would work just as well
for serial.

Dave Hylands
Vancouver, BC, Canada

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