If all you want is to measure is cable length, then just measure the cable capacitance (or cable pair C). Knowing your pf/ft it's simple math after you measure C. Many DVM's can measure C directly. Alternatively use the cable C in an RC osc cct and measure frequency or period. The cheap TDR URL posted earlier uses a 74HC14 as the oscillator. Just use the cable for the C and you're done. KISS! Remember to substact out the connecting lead C. Using a 555 and current source for charging C would give you a linear read out that you could display on an analog meter. (One half of 556 oscillates using cable C, the other half generates a fixed width pulse which you low pass filter and use to drive meter IOW FtoV). No PIC required . Robert michael brown wrote: > > From: "Dennis J. Murray" > To: > Sent: Thursday, February 20, 2003 1:40 PM > Subject: Re: [PIC]: How would I build a reflectometer? > > > I'll tell you guys - I've been following this link since it's > inception and > > you REALLY have my curiosity piqued!! I've used TDRs quite a bit in a > past > > life and I DEPENDED on the visual representation on the screen to > interpret > > what is really on the line! I don't think I EVER had a clean line > that > > didn't require some interpretation - was that hiccup a sharp bend? > water in > > the line? an unauthorized tap? A long-forgotten splice? etc. > > > > How do you plan to accomplish this using a PIC or an oscillator > circuit???? > > Or don't you? Just looking to determine overall length to the most > > significant reflection?? > > I only wanted to measure the length of installed network cabling. I'm > not really looking for wiretaps or anything that subtle. ;-) I'm > thinking that as long as the injection end is terminated to match the > characteristic impedance of the wire, there should only be one large > reflection and that would be from the far end. I'm thinking that using > the latest arriving "echo" would represent the distance to the far end > of the wire. > > michael -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu