All feet off the Internet throughout the era of the global village, the network has changed people's traditional way of life. Now that computer technology advances, broadband has been every family, and network access can take a variety of ways, such as unit LAN, ADSL, ISDN, MODEM, power line carrier broadband and so on. The most commonly used medium or five twisted pair connections, has been widely used network engineering. We often use to build the network RJ45 connectors, crimp tool used for a variety of interfaces, shown in Figure 1. The quality of the interface is very important, it affects the network connection is successful or not. Cable ready, the common network cable tester for testing. Here a simple cable tester works, you can DIY.

The cable tester in two units: one is the sending unit, using a 9V laminated battery-powered, and the power switch and green power light. The other is receiving unit, 5 LED indicates the network cable connection status. Circuit shown in Figure 3.
1. Transmission unit
Circuit shown in Figure 2, using three integrated circuits and a small amount of external components. CD4069 inverter is a six form the multivibrator and the LED drive circuit, CD4017 is a decade counter pulse divider. Assigned to the appropriate network cable test pulse, 74LS367 is a six-bus driver, to help produce cable test pulse.

2. Work
In Figure 2, CD4069 inverter inside the two N1, N2 and R1, C1, R2 constitute a positive feedback network, composed of multivibrator to produce a rectangular pulse. Pulse signals to the decimal counter / pulse divider CD4017's feet (CLK-side), CD4017's15 pin (RST side) when power is reset,13 feet (CKINF1 side) ground, the input pulse count. From Q1, Q3, Q5, Q7, Q9 and CO output pulse signal, QI positive output pulse added to D2, so D2 conduction. Q1 pulse signal at the same time added to CD4069 (U1A) of 1 feet, so that its output pin goes low 2, current through D2, the sending unit interface RJ45 1 feet, measured network cable, RJ45 interface, the receiving unit 1 feet, D11, receiver unit RJ45's 2 feet back sending unit. If D1 1 lights to indicate feet and 2 1 foot cable is the Messenger. D4 Q3 output pulse added to the cathode, while added to the six-bus driver 74LS367's 15 feet (E2-side) and the D4-side, the signal through 74L-S367 from the Q4 output high, the 4069's U1D inverter to send the unit RJ45 The 6 foot into a low current through transmission unit 3 feet, measured cable, the output to the receiving unit, after D13, receiving unit 6 feet of network cable to test the foot 3 and 6. Similarly, the output pulse from the Q5 feet added to D1 positive and CD4069 (U1B) of 3 feet, CD4069 (U1B) of the pin output low added 4 4 RJ45's feet, complete legs and 5 4 foot network cable test. Q7 positive output pulse added to the D3 and CD4069 (U1C) of 5 feet, complete legs and 8 7 foot network cable testing.
If the network cable connection errors, changes in flow through the circuit, LED status light changes, so you can determine the connection mode right or not. If the test is BNC interfaces, Q9 output pulse added to the positive and the 74LS367 in the D5 D5 and E1-side, Q5 output high level, by 4069 (U1D) down the other end of the phase added to the BNC, the BNC interface testing. 4017 the CO-side also will be added to the R4 output pulse by DIO, the power light flashes.
3. Test results
D11 said pin RJ45 of the state of 1 and 2, D12, said pin RJ45 to 4 and 5the state, D13 and 6 9 said pin RJ45 to the state, D14 and that 7 8 pin RJ45 to the state, D15, said BNC state. Normal network cable, LED is green; open circuit, LED off, LED light under the timing conditions can determine the network cable connection.