problem with rx 0

Hi, i ve hooked up a serial device outputing ttl 5v at 19200 baud to pin0 (rx) of my arduino, i ve uploaded a little sketch that with serial.Begin set to 19200 in the setup fonction. but nothing happen when i send data from the device to the arduino, should at least see the rx led blinking ?

( the serial device is fine, i ve just tested it with a teensy ).

should at least see the rx led blinking ?

The Tx and Rx leds are driven by the usb serial chip and only monitor data going to and from the PC, so they won't blink even when you get your external serial working. Did you also wire a ground from the arduino to the device?

Lefty

Post your sketch, lets see how you are reading the data coming in.
You cannot have the USB connected up while you are reading that data.

CrossRoads:
Post your sketch, lets see how you are reading the data coming in.
You cannot have the USB connected up while you are reading that data.

Well you actually can as long a the PC is not actively sending serial data via the USB link. There is a 1k ohm isolation resistor between the boards usb serial converter chip and pin 0, and a idle comm channel is a logic level high, so pin 0 acts like it has a 1k ohm pull-up resistor, which an external device's serial data output wired to pin 0 should have no problem 'overriding'.

Lefty

Oh ok that makes sense...so what are my option to monitor serial activity if can't use the usb connection, can is use program like realterm but only in listen mode ?
I l try to post the sketch when i get back home.

You could add to your sketch to blink the D13 LED when ever you read a byte in, something like that.

Try connecting the IDE Serial Monitor, maybe you'll have good results.

Actually you should still be able to use the standard Serial.print statements in your sketch to send debug data to your PC, even while you are receiving data on pin 0 from your external device, just make sure your PC does not send data to the board as that would result in possible collisions of data with the external device and cause garbling. Plus your PC serial monitor must be run at the same baud rate as your external device as the rx and tx must run at the same rate specified in the Serial.begin(speed) statement.