Essential Components of the Network Wiring Tester
In its fundamental design, the network wiring tester follows a universal blueprint, comprising two essential components: the transmitter unit, stationed at the network’s starting point and powered, and the passive receiver unit, which can be maneuvered from one socket to another. Both units feature eight LEDs, each distinctly marked from 1 to 8. Through the manual mode activated by a push-button or the automatic mode initiated by a clock, the eight LEDs sequentially illuminate on the transmitter unit. The objective is for the LEDs on the receiver unit to mirror this sequence precisely. By observing the cycle of LED illumination on the receiver unit, users can promptly detect any crossed wires. Moreover, this method allows for the immediate identification of open circuits (indicated when the corresponding LED fails to light up) and shorts (indicated when two or more LEDs light up simultaneously).
Transmitter Unit Circuit Design
The transmitter unit circuit is elegantly straightforward. It features a Schmitt-input NAND gate IC1.A, configured as a multivibrator with adjustable speed via P1. In addition, IC1.B functions as a basic debounce circuit for button S2, a crucial component in manual mode. The network tester offers the flexibility to choose between these two circuit outputs using switch S1. These outputs are then directed to IC3, a decade counter IC forced to count up to eight by connecting its Q8 output back to its reset input. However, the outputs of IC3 lack the ability to directly drive LEDs, particularly over circuits that may pose risks (e.g., short circuits). To overcome this, a ULN2803 is employed to drive the eight LEDs within the transmitter unit (D12–D19).
The ULN2803 is a composite network of eight Darlington transistors, each capable of handling up to 500 mA. This network not only powers the LEDs but also routes the signals to the socket, housing contacts O1–O8, where the wiring to be tested is connected. The corresponding receiver unit, situated at the opposite end of the cable, consists of eight LEDs (D20–D27) and their accompanying current limiting resistors. To ensure proper operation, there must be a shared connection between the transmitter and receiver units. In the case of shielded network wiring, the shield can fulfill this role. Alternatively, the earth wire of the electrical installation can be employed for the same purpose. However, if neither of these options is viable, you may need to incorporate a flying lead for this purpose.
Power Supply for the Transmitter Unit
The power supply for the transmitter unit is readily sourced from a ‘plugtop’ adapter, delivering approximately 9 V at around 10 mA. The supply voltage for IC1 and IC3 is regulated at 5 V, a measure that, while not strictly necessary, provides added stability. In cases of occasional, short-term usage, a 9 V battery may be used as a viable alternative.
Maintaining Consistency and Order for Functionality
If the network wiring tester is intended exclusively for network wiring testing, the connectors O1–O8 and I1–I8 will take the form of RJ45 sockets, with COM linked to their screening contact. To ensure seamless operation, it’s imperative to maintain consistent numbering for the LEDs in both the transmitter and receiver units. In instances where automatic mode will be employed, extra attention is required to ensure the LEDs are correctly aligned in order.