read rs232 from external device

Projects Networking, Protocols, and Devices
1

Hi, I need to read some data from an external device that has a rs232 port.
I'm using Arduino Uno.
In order to accomplish this, I can use the pin 0(RX) and pin 1(TX) or I have to buy an rs232 shield?
Thank you

2

It depends on the signal levels.

A normal RS-232 port uses signal 3...15V and -3...-15V.
The RX and TX of the Arduino Uno are called TTL level serial. The 'TTL' is an old name for logic 5V levels.
Some Arduino boards run at 3.3V, so those boards have 3.3V level signals.

So you need to convert the RS-232 to 5V levels with an adapter.
http://www.ebay.com/itm/1PCS-MAX232-RS232-COM-Serial-to-TTL-Converter-Module-Board-/251131170646

3

If you are just receiving, you can use a transistor and two 10k resistors like below to invert the signal.