I have the notion of putting together a TP cable tester with an arduino. I've seen hacks sending power and lighting up a LED to check continuity, and used a similar 'professional' tester that just plugged into both ends and sent power through one wire at a time, lighting up a LED if it's got continuity aswell. But, at one of the cables, it had intermittent failures when using it for real data, and often didn't work at all. Swapping out a connector, and straightening what appeared to be a kink in the cable, made it work again.
So, I would like to do a little project where first a regular cable test is performed (check continuity, and that there are no shorts between wires). And if that passes, sending out whatever high frequency an Arduino of any type (from Uno to Mega2560..) can produce, and reading it back on another pin. Using a TP plug in the other end that basically just cross-connects each colored pair, so that a signal can be sent out on one color (say, green) and be received on green-white as it comes back. This would give some hint at the testing end if the cable is okay enough to use with at least a few MHz frequency as opposed to just static DC to light a LED.
After having used a 'plain' cable tester on a 70m cable recently, and us then spending a couple of hours trying to find out why the hecko the full network was seen sometimes but then dropping out again, I'd like to DIY a cheap solution to at least help track down simple problems like this.
(It didn't help matters that when the main switch managed to connect to a single test unit, but freaked out when connected to a switch at the other end as it was supposed to, so for a long time we thought the cable was okay because 'it works just fine with this one unit, must be something in the switch..')
Anyway.. well, I hope you see what I'm getting at. For cheap, testing one pair at a time with some frequency and matching the results or showing dropouts would probably be fine. And having it built into the same unit that first checks for continuity and short circuits means that it can do all the tests without risking shorting out the network buffer/chip on a 'real' machine, like a work laptop.