TDR kit built

My Time Domain Reflectometer (TDR) circuit has been available as kit made by Far Circuits. The kit consists only of circuit board and components needed to build the circuit in a small plastic bag (you need to download the building instructions).


The original circuit design is from my web page and Far Circuits added 5V regulator and designed the circuit board.

I have written some information about the TDR kit earlier, but now you have more. I just finished building my own kit sample some days ago.


Around half of the components on the kit are SMD components and half of the components are traditional through-hole soldered components. I was pretty easy to build, no problems there. I used lead free solder to build the circuit even though it might not be optimal solder if some components contains lead.

I first soldered the SMD components to clean circuit board using pinbypin method. Then I assembled the through hole components to their places and solder them.



The kit worked well but with some reduced performance compared to my original design. The original circuit design used pretty high speed 74AC14 IC, but this kit I received used a slower speed 74HC14 IC. That was the actual IC that was in component bag instead of 74AC14 as listed on the component list.

Things seen on the pictures not included on the original kit: IC socket, pins to connect wire to, jumper wire connected between two pins to select the pulse length and the wired feeding power to the circuit.

NOTE: The first kit versions were shipped with 74HC14 IC. According to Farcircuits the newer kit versions are shipped with 74AC14 IC.


  1. Tomi Engdahl says:

    Ask Hackaday: Is Our Power Grid Smart Enough To Know When There’s No Power?

    Bouncing Pulses Along Your Power Lines

    Time domain reflectometry is an extremely simple process that relies on the property of a traveling waveform to bounce off the end of a transmission line and be reflected back to its originator. It’s a standard lab experiment for electronic engineering students that can easily be replicated with a pulse generator, a coil of cable, and an oscilloscope. Adjust the ‘scope to see the end of the generated pulse, and there a short time later will be its reflection. The time between the end of the sent pulse and the arrival of the reflection is the time it has taken to travel the length of the cable and back again, so from that the length of the cable can be calculated.

    Since the pulse will reflect from any faults, the distance to the fault can also be worked out. Once the breaker has been triggered by the fault the electricity company can measure the distance, and send out a repair team to fix it. That’s exactly how an El Segundo steam plant located a fault in ten miles of buried cable.

    Find And Repair A 230kV 800Amp Oil-Filled Power Cable Feels Like Mission Impossible

    Finding out the location of the fault itself was quite a feat. It involved time-domain reflectometry (inconclusive), ultrasound, and radar (didn’t work) and then using an Impulse Generator-Tester (Thumper) which got them pretty close to the defective segment. What pinpointed the problem was a bunch of car batteries and some millivoltmeters. They hooked up car batteries to both ends, tapped the cable at several points and knowing the drops and resistance of the cable, got within a few feet of the fault. Finally, X-Ray equipment was brought in.

    The failure was attributed to “TMB”, short for Thermal Mechanical Bending. TMB causes the cable to wiggle in place due to load surges. This eventually causes insulation failure due to abrasion against the pipe and separation of the many layers of paper tape.


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