3volts interface to MC serial port

[Peter Nabil]

Hi every single one
i've a GPS module deals with the serial port of the MC,
my problem is the GPS module deals with 3 volts ( Tx and Rx ),
for the Tx of the MC i used a variable resistance as a voltage divider in order to reduce the input signal for the module, so what about Rx of the MC ,
shall i connect the output of the module ( 3v ) directly to the Rx of the MC directly ?!!!! from 3v to 5v !!!!!! i am goin' crazy, some body help me please,
i am afraid to connect that directly, i can feel this goin' to damage the module,
if i am wrong somebody tell me , i am wrong,
if not, somebody tell me the solution of my problem
:roll:

 

[Nigel Goodwin]

Hi every single one
i've a GPS module deals with the serial port of the MC,
my problem is the GPS module deals with 3 volts ( Tx and Rx ),
for the Tx of the MC i used a variable resistance as a voltage divider in order to reduce the input signal for the module, so what about Rx of the MC ,
shall i connect the output of the module ( 3v ) directly to the Rx of the MC directly ?!!!! from 3v to 5v !!!!!! i am goin' crazy, some body help me please,
i am afraid to connect that directly, i can feel this goin' to damage the module,
if i am wrong somebody tell me , i am wrong,
if not, somebody tell me the solution of my problem
:roll:

Just connect the signal directly - you can't damage the module by connecting it's output to a logic input, and 3V logic is within normal 5V logic specifications. Certainly PIC's work quite happily like that, though you might like to add a series resistor between them, in case the input pin gets switched accidently to be an output!.

The other way might, or might not, require a potential divider - it depends on the design of the input circuit. If it was a PIC, a simple series resistor is enough, the internal protection diodes will clamp it to the supply rails, the series resistor is just to limit the current through the diodes. But using a potential divider won't do any harm anyway, and it's probably not worth the risk for the cost of a single resistor.