avr_fred:
Another time waster with the OP withholding very pertinent information because he thinks it doesn’t matter. Twenty two posts to find out the actual use is totally different than the use outlined.Testing a faulty line line involve checking line to ground rather than isolating it from ground for use. There are dozens of existing devices and designs for line quality checking and for line identification. For ID, Fox and hound testers have been around for a long, long time.
Please Read my original post:
TAJS-C:
It's essentially working on a project with telephone lines, and I would like to be able to identify when somebody manually sends basic 1/2 second pulses of Negative voltages of more than -12V up to -50v in order to change the state of the arduino.
I was not going to overshare the rest of the project, as it is already finished. There is no point in over-complicating a simple question.
Yes, there are Far-end devices out there that can do the job, but the ones available here that are compatible with our testers cost many HUNDREDS of pounds.
I'm making something similarly useful, if not superior in some ways, for <£40.
So, although I appreciate your help, but I found your comment to be non-factual and rude.
Please re-read and rethink, but I feel I provided more than enough information for what I required- as proven by the fact that another poster instantly responded with an answer that works perfectly. (A reply of thanks to follow)