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PIC RJ-45 Cable Tester Schematic Circuit Diagram

This RJ-45 cable tester automatically checks cable continuity and tests the connection configuration. Each of the eight connections is checked independently and short-circuits are detected.

PIC RJ-45 Cable Tester Schematic Circuit Diagram

Choosing the Suitable Microcontroller

The circuit can be constructed using either a PIC16C62B or a PIC16F72 microcontroller. The reason behind selecting these options is the presence of 22 input/output pins on these microcontrollers. Each RJ-45 socket requires eight input/output pins, totaling 16, and two additional pins are allocated for the LEDs.

Power Supply and Microcontroller Selection Considerations

For the described tester, the PIC16C62B is employed, operating at a supply voltage of 3 V. This choice necessitates a power unit with two batteries. However, this microcontroller can only be programmed once. Alternatively, the reprogrammable and pin-compatible PIC16F72 can be used, albeit requiring a three-battery power unit to attain a voltage of 4.5 V. The clock circuit, comprising R1/C1, provides a cost-effective solution as an accurate clock frequency is not essential.

Operation and Testing Features

The circuit initiation is triggered by the push-button (BP), and the power is controlled through transistors T3 and T2. It automatically ceases operation after a delay initiated by Timer0. Timer0 overflow generates an interrupt, causing pin RA0 to go low. Consequently, transistor TQ2 turns off, followed by T3. The LED bargraph facilitates the monitoring of each connection test. The first LED (pin 1) illuminates if the cable is in good condition. The second LED (pin 2) indicates a wiring or continuity fault. Both LEDs light up in the presence of a short circuit. The remaining eight LEDs demonstrate the cable connection status. In a properly functioning cable, a left-to-right chaser pattern is observed; however, if the cable is crossed, a back-and-forth chaser pattern is displayed—resembling Kitt from the cult TV series ‘Knightrider’.

The software in assembler code is available on [1].

www.elektor.com/090643

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