Homemade simple network cable tester

In the era of the global village where the Internet is everywhere, the Internet has changed people's traditional lifestyle. Now computer technology has made great progress, and broadband has entered thousands of households. Network access can be achieved in many ways, such as unit LAN, ADSL, ISDN, MODEM, power carrier broadband, etc. The most commonly used connection medium is still Category 5 twisted pair, which is now widely used in network engineering. When we build a network, we often use RJ45 connectors and use crimping pliers to make interfaces of various specifications, as shown in Figure 1. The quality of the interface is very important, which affects the success of the network connection. After the network cable is made, it is often tested with a network cable tester. Here is a simple working principle of a network cable tester, which you can DIY.



The network cable tester is divided into two units: one part is the sending unit, which is powered by a 9V laminated battery, and has a power switch and a green power indicator light. The other part is the receiving unit, which has 5 light-emitting diodes to indicate the network cable connection status. The circuit is shown in Figure 3.

1. Sending unit

The circuit principle is shown in Figure 2, which is composed of 3 integrated circuits and a small number of peripheral components. CD4069 is a six-phase inverter, which forms a multivibrator and LED driver circuit. CD4017 is a decade counter pulse distributor. It distributes appropriate test pulses to the network cable. 74LS367 is a six-phase bus driver, which helps to generate network cable test pulses.



2. Working principle

In Figure 2, the two inverters N1 and N2 inside CD4069 and R1, C1, and R2 form a positive feedback network to form a multivibrator and generate rectangular pulses. The pulse signal is added to the ⒁ pin (CLK terminal) of the decade counter/pulse distributor CD4017. The ⒂ pin (RST terminal) of CD4017 is reset when power is applied, and the ⒀ pin (CKINF1 terminal) is grounded to count the input pulses. The pulse signal is output from Q1, Q3, Q5, Q7, Q9 and CO. The pulse output by QI is added to the positive pole of D2 to turn on D2. The pulse signal of Q1 is simultaneously added to the pin ① of CD4069 (U1A), making its output pin ② become low level. The current returns to the sending unit through D2, pin ① of the sending unit interface RJ45, the network cable under test, pin ① of the receiving unit interface RJ45, D11, and pin ② of the receiving unit RJ45. If D1 1 is lit, it means that the network cables at pins ① and ② are connected. The pulse output by Q3 is added to the positive pole of D4, and is also added to the pin ⒂ (E2 end) and D4 end of the six-bus driver 74LS367. The signal outputs a high level from Q4 through 74LS367, and is inverted by U1D of 4069 to make pin ⑥ of the sending unit RJ45 become low level. The current is output to the receiving unit through pin ③ of the sending unit and the network cable under test, and then passes through D13 and pin ⑥ of the receiving unit to test pins ③ and ⑥ of the network cable. Similarly, the pulse output from Q5 pin is added to the positive electrode of D1 and the ③ pin of CD4069 (U1B). The ④ pin of CD4069 (U1B) outputs a low level and is added to the ④ pin of RJ45 to complete the test of the ④ and ⑤ pins of the network cable. The pulse output from Q7 is added to the positive electrode of D3 and the ⑤ pin of CD4069 (U1C) to complete the test of the ⑦ and ⑧ pins of the network cable.

If the network cable is connected incorrectly, the circuit flowing through changes, and the light-emitting diode lighting state changes, so it can be determined whether the connection mode is correct or not. If the BNC interface is tested, the pulse output from Q9 is added to the positive electrode of D5 and the D5 and E1 terminals of 74LS367. Q5 outputs a high level, which is inverted by 4069 (U1D) and added to the other end of BNC to test the BNC interface. The CO terminal of 4017 will also output a pulse and be added to DIO through R4, and the power indicator light will flash.

3. Test results

D11 indicates the status of RJ45 pins 1 and 2, D12 indicates the status of RJ45 pins 4 and 5, D13 indicates the status of RJ45 pins 9 and 6, D14 indicates the status of RJ45 pins 7 and 8, and D15 indicates the status of BNC. When the network cable is normal, the LED is green; when it is open, the LED is off. The network cable connection status can be determined based on the LED lighting sequence