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.
The circuit can be built using either a PIC16C62B or a PIC16F72. This microcontroller was chosen, as it has 22 input/output pins. Each RJ-45 socket uses eight input/output pins, i.e. 16 in all, plus two I/Os are used for two LEDs.
The tester described is built using the PIC16C62B, which can work with a supply voltage of 3 V, justifying the use of a power unit with two batteries. Unfortunately, this microcontroller can only be programmed once. It is possible to use the PIC16F72, which is reprogrammable and pin-compatible, but you’ll need to use a three-battery power unit to achieve a voltage of 4.5 V. The clock circuit is formed by R1/C1, a cheap solution, since we don’t need an accurate clock frequency.
The circuit is started using push-button ??BP, the power is maintained and controlled by transistors T3 and T2. It stops automatically, after a delay generated using Timer0. When Timer0 overflows, an interrupt is produced which leads to pin RA0 going low, and in this way transistor TQ2 turns off, followed by T3. The LED bargraph allows us to follow the testing of each connection. The first LED (pin 1), ontrolled by RA2, lights if the cable is good. The second LED (pin 2), controlled by RA3, lights if the cable has a wiring or continuity fault. Both LEDs light if the cable has a short circuit. The other eight LEDs show how the cable is connected. If the cable is all right, we see a left>right chaser; but if the cable is crossed over, we get a back-and-forth chaser — just like Kitt in the cult TV series ‘Knightrider’.
The software in assembler code is available on .