Serial Data from Arduino Diecimila


I have an Arduino Diecimila, which is a USB type board. I am attempting to get the Ardiuino to send serial data to my PC using one of the 9pin D-type com ports wired from the TX/RX arduino pins.

I have the arduino connected to the PC with virtual COM4 over the USB link so I can program the board. In my prog I use the serial.println function. With this I can see the data appear in the "serial monitor" on COM4.

I then connect the following pins on my PCs COM1 D-type serial port: arduino pin 0 RX to PC pin 3 TX arduino pin 1 TX to PC pin 2 RX arduino pin 14 to PC pin 5 signal ground

When I disconnect the USB connector and reboot the arduino, I either get complete nonsense when I monitor the output on D-type COM1 port from with in Hyperterminal on my PC... or I get nothing at all.

I have hyperterminal set to 9600-8-N-1 (none), which is also set by Serial.begin(9600) in my program.

... it looks almost as if the RX/TX serial communications is conflicting between going out over the USB, with simultaneously running the Arduino serial pins. To support this theory, if I connect the D-type serial pins and USB at the same time, the IDE locks up when attempting to send the binary program to the arduino.

Has anyone experienced this before or shine any lights on how I can make serial serial output that I can read from a d-type serial interface on my PC?

Any help would be gratefully received. Thanks in advance...


You need one of these:

You can make your own for a few bucks. The Arduino is putting out ttl and your computer is expecting rs232. A quick google search will provide a ton of details.

Your problem is because of incompatable voltage levels. The Arduion digital input and out pins work at a 0vdc or 5vdc levels. A 9 pin RS-232 serial port uses voltage levels of (+3 to +15vdc) or (-3 to -15vdc) for it's logic levels. You need to use a voltage convertor to utilize a RS-232 interface for a Arduino application. Here is one example:

If you wish to DIY then a MAX232 convertor chip and some caps will accomplish the same task.