This is a simple RS232 cable tester. It can be used to quickly diagnose communication problems, due to cable/port defects or software bugs. Useful on those situations where you can’t connect an oscilloscope or multimeter to debug a problem.
Basically, there are two rows of LEDs, one for a high level signal and one for a low level signal. The LEDs in these rows represent every RS232 signal: TXD, RXD, RTS, CTS, DTR, DSR, DCD and RI for a full modem RS232. The corresponding LED will lit depending on the signal level. There is no need of power supply: the LEDs are powered directly from the RS232 signals.
The board has a female DB9 connector on one side and a male DB9 connector on the other side, so it’s easy to connect.
If you want to intercept the ongoing communication with an oscilloscope, there is a a row of 0.1″ (2.54mm) pins to place probes. This saves you from stripping cables or interrupting the communication.
There are also four mounting holes to fix the board to a static location.