Lightweight and practical multi-core cable detection circuit

This circuit can check whether the two ends of a bundle of wires or a multi-core cable are the same bundle of wires or the same cable, can check whether there is a wire break or short circuit in a bundle of wires or a cable, and can calibrate the wire numbers at both ends of a bundle of wires or a multi-core cable. This circuit has the advantages of small size, light weight, simple operation, easy use, fast and accurate inspection, low power consumption, etc. It has certain reference significance in practical applications.

Working principle of the circuit. The circuit schematic is shown in the figure below. The whole machine is powered by a 9V dry battery. When the power switch S1 is turned on, the whole circuit is powered, the power indicator LED2 lights up, and the NE555 integrated chip starts to work. Its working state is multi-harmonic oscillation. Pin 3 outputs a rectangular pulse with a duty cycle of about 50%. LED1 starts to flash at this time. The pulse is input to pin 14 of the CD4017 integrated chip. At this time, CD4017 starts counting and outputs a high level in turn. This high level reaches each port of P1 through the resistor. A multi-core cable is connected between P1 and P2. If each line of the multi-core cable is turned on, LED3-LED10 will be turned on in turn and flash; if one line of the multi-core cable is disconnected, the corresponding LED light will not light up; if the line number of the multi-core cable is wrong, the order of diode light emission is wrong. Through this principle, the purpose of detecting multi-core cables is achieved.

Work debugging. Close switch S1, turn on the power, LED2 lights up, and use your hand to feel whether the main chip is hot. There is no abnormal phenomenon. Later, it was found that LED1 would not flicker, and the problem appeared. It was guessed that the 3rd pin of the NE555 chip did not output a pulse wave. Using an oscilloscope to detect, there was indeed no waveform output. At this time, carefully check whether the soldered circuit has a short circuit or a circuit break. Use a digital multimeter to detect whether each connection point is conductive. It was found that there was no abnormality in the line. Check the information about the NE555 chip, especially the connection method of each pin when used as a multivibrator. Analyze that the 5th pin of NE555 is not connected to the ground by a capacitor, which is easy to cause high-level crosstalk. So add a 4.7μF capacitor to the ground at the 5th pin of the NE555 chip to eliminate the high-level crosstalk; turn on the power again, use an oscilloscope to detect the waveform of the 3rd pin of NE555, and measure that the 3rd pin outputs a pulse wave with a duty cycle of about 50%, and LED1 flickers. Use a good network cable for testing. After power on, it is found that the light-emitting diodes LED3~LED10 light up in turn, and the frequency of the light emission can be synchronized with LED1, that is, when LED1 lights up and flashes once, one of LED3~LED10 lights up and flashes at the same time. Finally, cut one line in the network cable for testing. After power on, the corresponding LED5 does not light up, and the remaining 7 LED lights can light up one by one, and can be synchronized with LED1, so the detection is successful.