Serial Problem

I am using an Arduino Diecimilla.

My problem is that when I try to print to serial, e.g. Hello World. I can see the output using the included Serial Monitor.

However, when I try to view the output using other terminals such as Hyperterminal or Python. I can't seem to read any character.

Help please :(

Have you selected the correct port? Have you selected the correct bit rate? Have you selected the correct data format (8 data, one stop, no parity)? Have you turned off hardware and software handshaking? Does the Tx LED blink?

Thank you for the reply.

I checked for the following settings and applied them to the Hyperterminal. However, I still cannot display the output.

My Arduino board does not have a Tx LED.

Post your Arduino Sketch (please use "code tags").

The Diecimilla should have Tx and Rx LEDs...

You did close the Serial Monitor window before trying to connect to the Arduino using another serial connection, right?

Yup. I did closed it.

I was able to open a connection to the COM port which means no other program such as Serial Monitor is accessing it. I ruled out baud rate error since I must still receive garbage characters but instead I cannot receive any.

It is really baffling.

I am using a modified Arduino board so it does not have Tx and Rx LEDs.

I used the “Hello World” sketch from the examples.

I used the "Hello World" sketch from the examples

That is not good! You have to do it in a loop.

As you are using a modified board a lot of things can happen during the reset phase.

Standard Arduinos sport a capacitor which differenciates the DTR signal to a reset pulse. When yourboard does not do it, it will stay reset by communication program which insist on holding the DTR low....

The Hello World sketch actually does printing "Hello World" in a loop


Just to satisfy my curiosity I looked at the difference between Hyperterminal and Arduino Monitor signals.

Hyperterminal - in contrast to Arduino Monitor - toggles the RTS line (low), which does not cause any effect on most Arduinos. I looked into the drawing and found a 100 Ohms resistor R2 which should in fact force a permanent reset condition in that case. A sharper look at my boards showed however that this resistor was not installed! For obvious reasons...

If this 100 Ohms resistor between pin 3 of the FTDI chip and reset is installed on your (modified) board, then this is a perfect explanation for the situation...

Best remove it, as there is little use for it....

Be careful! I should not have recommended to "remove" anything from your board ;D The schematic of the Diecimille e.g. shows TWO 100 Ohms resistors each from RTS and DTR.

In this case the 100 Ohms will (though hardly) prevent the reset condition in case DTR is is low and RTS is high....

We need to know your board to find a solution.

Note: I used the voltage of the FTDI chip output when saying "high" or "low", which is inverse to what is on the RS232 lines....