Once upon a time somewhere in 2015 i bought a couple of these little converters RS232 tot TTL.

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Here is how they work

From the RS232 Port – RX, TX and GND.  Thats the -> -<and the – signs.  Easy enough

– GND

-> RX

<- TX

On the TTL (Arduino)  side – DO NOT USE 5V use 3.3V as this toasts the device and heats up and like tops itself.  It certainly got very toasty when I put 5V across it.  This could be because I messed up somewhere in the wiring but it certainly works well for me.  I can also use the SoftwareSerial library as well so I don’t need to use TX/RX on the TTL Serial pins 0 and 1

So TTL is

– GND

-> – PIN X

<- PIN Y

For my device I used PIN 0 and PIN 1 – TX/RX – but I guess you can use other pins.

TTL RS232 Pinouts
TTL RS232 Pinouts

 

 

 

Hope this helps – it does work!