Once upon a time somewhere in 2015 i bought a couple of these little converters RS232 tot TTL.
Here is how they work
From the RS232 Port – RX, TX and GND. Thats the -> -<and the – signs. Easy enough
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
-> – PIN X
<- PIN Y
For my device I used PIN 0 and PIN 1 – TX/RX – but I guess you can use other pins.
Hope this helps – it does work!