HiLetgo 5pcs RS232 to TTL Converter Module COM Serial Port Board MAX3232 MAX232CSE

I was using this to convert the TTL from the Arduino to the RS232 of my Stone HMI display. Then I got brave and removed the 4 SMT resistors on the Display and re-soldered them on the TTL line. Now I don't need these, but they were very good for testing functionality before doing surface mount soldering...

Great product for the money. Mine were all RS3232 chips and output correct voltage. Unfortunately, the pin labled txd is actually rxd and rxd is txd. A lame mistake by the maufacturer but once you know, they work well. Using this for serial testing with a LibreComputer "Le Potato" connected to pins 4,6,8,10 which map to /dev/ttyAML6 once you "ldto enable uarta". I would buy more but this came with 5x units. All set for four more projects.

First, all of these worked so no complaints there. Contrary to what I'm reading here, RX and TX silkscreens are NOT labeled backwards. But the spec on a DS232 I.C. REQUIRES +5V for VCC. These chips are not designed to operate at 3.3V. If your circuit needs a 3.3V TTL level from/to this device, use an open collector component, such as 2N4401 or 7406 with 1K pullup resistor to level shift the 5V TTL down to 3.3V

Hooked TX to TX and Rx to Rx. Worked fine with an USB to rs232 adaptor on the other end.

These allow connections to RS232 lines and convert to TTL level signals, all units work as advertised