This project is a Cable Fault Detector based on Time Domain Reflectometry (TDR). It helps in identifying faults in cables by sending a pulse and analyzing the reflected signal.
- A pulse is sent down the cable.
- If there is a fault, the pulse is reflected back.
- The time taken for the reflection helps determine the location of the fault.
A compact Time Domain Reflectometer (TDR) add-on for oscilloscopes, featuring two pulse generation methods:
- Schmitt-trigger (74AC14) pulse generator for coarse/long-range scans
- Avalanche transistor + Cockcroft–Walton multiplier for high-voltage, ultra-fast pulses and high-resolution fault localization
This README covers design intent, differences between pulse modules, calibration notes, safety warnings, and future improvements.
- Dual pulse sources for multi-resolution TDR testing (coarse scan and high-resolution probe)
- Simple oscilloscope interface
- Configurable resistive splitting/termination for high-impedance and 50 Ω setups
- Battery operation for low-voltage stage; compact voltage-multiplier for high-voltage stage
- Generates square/short pulses using a hex inverter
- Low voltage operation (~4.5 V)
- Suitable for long, lossy cables and coarse fault location
- Simple, low-cost, compatible with common oscilloscopes
- High-voltage, ultra-fast pulse generation for high spatial resolution
- Uses oscillator, flyback inductor, voltage multiplier, and avalanche transistor
- Suitable for short cable segments and fine fault localization
- Requires careful handling due to high voltages
- Use BNC T-piece and scope's high-impedance input for general testing
- For 50 Ω setups, use matched resistive splitter and terminated path
- Connect TRIG output to oscilloscope external trigger for stable traces
| Pulse Length | Frequency (approx.) | Blind Spot | Practical Range |
|---|---|---|---|
| 10 ns | ~50 MHz | ~4 m | up to ~500 m |
| 50 ns | ~10 MHz | ~8 m | longer than 10 ns |
| 200 ns | ~2.5 MHz | ~30 m | up to ~1.5 km |
| 1 µs | ~500 kHz | ~100 m | up to ~5 km |
| 5 µs | ~100 kHz | ~600 m | very long range |
Note: RG-58 is a 50 Ω coaxial cable; RG-59 is 75 Ω. Always match termination to cable impedance to avoid reflections.
- High-voltage stage can reach several hundred volts; treat all high-voltage areas as live
- Discharge capacitors safely before handling
- Only work on high-voltage stage with proper experience and equipment
- Use proper grounding for oscilloscope probe
- Improve pulse shaping for even higher resolution
- Add automated calibration routines
- Enhance safety features and enclosure design
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Cockcroft, J. D., & Walton, E. T. S. (1932). "Experiments with High Velocity Positive Ions." Proceedings of the Royal Society of London, Series A, 137(831), 229-242.
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Furse, C., & Haupt, R. (2001). "Down to the wire." IEEE Spectrum, 38(2), 34-39.
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Smith, P., Furse, C., & Gunther, J. (2005). "Analysis of spread spectrum time domain reflectometry for wire fault location." IEEE Sensors Journal, 5(6), 1469-1478.
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Agilent Technologies. (2006). "Time Domain Reflectometry Theory." Application Note AN-1287-2.
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Nahman, N. S., & Guillaume, M. E. (1980). "Deconvolution of time domain waveforms in the presence of noise." NBS Technical Note 1047, National Bureau of Standards.
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Andrews, J. R., & Bell, B. A. (1982). "Broadband sampling oscilloscope techniques." IEEE Transactions on Microwave Theory and Techniques, 30(11), 1913-1920.
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Hippel, A. R. (1954). Dielectrics and Waves. John Wiley & Sons, New York.
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Texas Instruments. (2013). "74AC14 Hex Schmitt-Trigger Inverter Datasheet." Literature Number: SCLS089J.
Note: This project was developed independently, incorporating principles from the above references and standard TDR literature.
All images used in this project are located in the Images folder.