RS-232 Loop Back Test

I have and electronics background but have not done much lately can getting back into it.

I need to test RS-232 cables. I would like to be able to use Arduino to do the following but I have not yet connected the dots:

I would like to be able to hit a button have the unit send out a string of characters via RS-232, have it read the string, and the light a Red LED if the comms did not receive the proper string or a Green LED if the string was correct.

I know I need to cross connect the end of the cable to get the loop back part.

The second part of the project (could be separate unit if needed) is do the same as above but with cables that have the USB to RS-232 Chip in the cable. I am not sure how the different chip sets will affect this project. Those different chips may not allow this project to work properly.

Thanks in advance,

Jeff - W7GRV

If you have a cable built right, why do you even need to send characters?

At one of my former jobs, we checked continuity and that is it.

The Arduino uses TTL level signals so you cannot connect RS232 directly to it you need a shield.
However since the Arduino will be both sending and receiving in this case that does not matter.

A lot though depends on the exact configuration of RS232 cables. At the most simple they have Rx , Tx and signal ground. However some cables also use signals for hardware handshaking so that the transmitter does not send characters too fast for the receiver to process. You could probably use the Arduino I/O pins to check the connectivity but to accurately simulate RS232 you might want to go back to having a shield.

For testing a bare cable you follow their spec and check for broken, shorted or wrong connections.

The cable with the USB converter is a special thing. You have to connect proper (expected) signal transmitters and receivers to both ends, and check for proper transmission. This may include RS-232 level shifters or line drivers/receivers, and a PC program at the USB side. I'd test pairs of such cables with a null modem in between, and use PC programs to send on one USB port and receive at the other port.

How many conductors in your cable? Any shield? What type connector?