Data sniffer box

Something easy to build that doesn't require any programming :-) and can be quite useful.

You need a few 9p RS232 type connectors (male and female), one diode like a 1N4148 and a 2.2K resistor.

Schematics is from https://www.lammertbies.nl/comm/cable/rs-232-spy-monitor

Pay attention to RX and TX connections.

DUT means Device Under Test and should be a device that transmit/receive serial data. It has to have RS232 levels. You may need a cross-cable to cross RX and TX if necessary.

You need 2 COM ports and I know it can be difficult these days (2022) to have a PC with 2 serial ports. To sniff the data, you can use PuTTY, Termite. You have quite a few options.

There is a possibility to connect a bluetooth module (BT) and replace one physical COM port. More about this option in another discussion. Obviously, your PC would need a BT module attached to a USB port.

Schematics:

Little box 3D printed: