My goal is a very basic one: I want to communicate from my microcontroller to my PC/phone via RS232.

I bought a TTL/RS232 converter like this.
And since my PC does not have a RS232 port I am using a RS232/USB cable like this.

I did the setup to my best of knowledge, but when I connect the USB end of the cable to my PC, it is not recognized as a serial device.

Therefore my question:
At what point should my device be recognized as a serial device (COMx) on a Windows PC? Would powering the TTL/RS232 converter be sufficient or does the microcontroller need to send something specific or just anything at all?


My setup and what I have done and tried so far:
The microcontroller I use for testing is a NodeMCU ESP8266 module.

I connected it to the converter like this:
VCC --- 5V / 3.3V (which both should work with the converter module)
RX --- TX
TX --- RX

And then I hooked that up to my PC with the RS232/USB cable.

The schematic that came with the converter looks like this (I noticed however that the actual hardware I got does not have a 4x2 header): TTL/RS232 converter schematic

There is plenty of code out there for writing data to a serial connection with Arduino. I tried writing to the hardware serial and also a SoftSerial with two safe pins on the ESP controller. I don't want to go into detail here, as long as I lack such basic understanding of the problem^^.

Sadly, I do not own an oscilloscope to watch the converter output.

Thanks for any pointers! :)

  • 1
    \$\begingroup\$ The device should be recognized as soon as USB is connected to PC. Nothing connected on the RS232 side can affect this, so unfortunately either the cable or USB port is broken if the PC cannot see that device is connected. If it does see the device, then it is a driver issue if it does not show up as COM port. Post a link to the adapter, it looks weird if it has two USB cables. \$\endgroup\$
    – Justme
    Nov 5, 2020 at 8:55

1 Answer 1


The adapter in the picture does not work with a PC.

Only the MicroUSB cable will connect as serial port to smartphone in OTG mode.

The standard red USB-A connector is only for providing charging power to smartphone.

Use a standard USB-RS232 adapter with a PC.

  • \$\begingroup\$ Thanks for the hint :) I will get another USB-RS232 cable and check again \$\endgroup\$
    – bLind
    Nov 5, 2020 at 11:24
  • \$\begingroup\$ Got another cable, works. Thanks @Justme \$\endgroup\$
    – bLind
    Dec 4, 2020 at 16:06

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