michael brown wrote: > > From: "Wagner Lipnharski" > To: > Sent: Thursday, February 20, 2003 3:42 PM > Subject: Re: [PIC]: How would I build a reflectometer? > > > hehe, again, I take back what I said in the last email, sent seconds > ago. > > You are in true trying to measure the wire distance. > > > > If you build a cable loop terminator, simply a connector to make a > loop > > between the cat-5 wires, lets say, building a 4 pairs loop, so you are > > multiplying by 8 the cable distance, and using any low cost thing as I > > suggested, a million pulses repeater, measuring the time, you could do > it > > with less than $10 hardware. > > I'm going to work on this in my "spare" time. ;-) I recently noticed > that a couple of "cheap" tools were available that would measure a > cable. Since the time to send a pulse and receive a response is very > short (nanoseconds), I had wondered how these tools could do it using an > inexpensive micro. Sampling. You generate a fast ramp whose slope is based on cable dielectric constant and have a damn fast comparator to sample the signal at a progressive delay (rising reference) after pulse is launched. The micro does the A/D conversion at it's leisure since the sampling process can be as slow as required by the A/D speed. The only 'hard' part is making a damn fast sample and hold (picosecond aperture times). There was a project in Circuit Cellar in the past decade that used a garden variety micro to do something similar to what you want. I looked on their site but didn't find it. Someone else here probably knows what article I'm thinking of. Robert -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu