I have a USB 2 Serial adapter and the device is working fine. I see the device perfectly configured in my System.

I have connected the TX0 pin of Arduino to DB 2 pin (read pin) of the adapter. Below is my Arduino code:

int i = 0;
void setup()

void loop()

But when I try to read thru terminal software of data received at my COM port I see some junk character incoming. I am pretty sure that I am using same baud rate / flow setting both side. Why am I facing this issue - do I need to connect any other pins also as I just need to receive data at system side?

1 Answer 1


I have a USB 2 Serial adapter...I have connected the TX0 pin of Arduino to DB 2 pin (read pin) of the adapter.

You must not connect Arduino pins directly to a D-SUB connector of a USB-Serial adapter, as those connectors traditionally carry higher voltage, opposite sense RS232 signals.

  • The voltage is too high, and likely to cause damage to your Arduino's processor
  • The signal is inverted in sense from the logic-level signaling used by your Arduino's processor.

If you actually needed to make this connection, you would need to either use a "logic level" USB serial adapter (sometimes informally called a USB-TTL adapter). These terminate in various types of connections such as bare wires or header pins/sockets - but basically never in an D-SUB connector. Or you can use an inverting line driver and receiver such as the MAX2232 type devices, or even an old 1488/1489 pair.

But it's not clear that you should be doing this at all - an Arduino Mega already has a USB-serial converter onboard - that is the interface you use to program it, and it would ordinarily be simplest to use that for runtime communication as well.


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