This simple AVR ATtiny2313-based LAN tester allows you to check the type of LAN cables (straight or cross) and to test whether LAN cable is broken or not. The project has 8 outputs. Each one of them produces a pulse successively and only one output can be high at any time.
To check the LAN Cable, you need to plug the end cable to rj45 connector A and the other cable end to RJ45 connector B. And then the MCU will send pulse to connector A and the LEDS will glow one by one for straight LAN cable and glowing changes to 1,2,7,4,5,8,3,6 for cross wire. If a wire is broken, the corresponding LED will not glow.
If both ends of the cable are not close enough to be plugged onto the circuit, you can use a remote board, which has only one rj-45 connector and 8 LEDs. Then plug one end of the cable to connector A on main board and connect the other end to the remote unit. This practical LAN tester is designed by Vasilis Stergiopoulos.
Cable Tester Tools
Project Detail and Documentation