Lab Description The TCT lab is about
building a Twisted-Pair Cable Tester. Students build and learn how to use
the tester to check Ethernet 10Base-T or 10Base-Tx cables. Since the cable
wiring configurations are the same, tester can be used with CAT3, CAT5, and
CAT6 cables. The circuitry has been designed for minimal current
consumption with 4 x AA batteries, so it can be easily built as a portable
tester. TCT circuit can detect
opens, shorts, crossed wires, and crossed pairs. A counter driver applies
all 8-bit combinations to the cable and compares the input with the output.
The counting is stopped if a problem is detected, and the wire in question
is indicated on a separate set of LED indicators. A buzzer also provides
audible alert when a fault is detected. Three connector
sockets for the RJ45 cables accommodate both straight thru and crossed
patch cables. ·
Dual Timer/Oscillator
(1) ·
Dual 4-Bit Binary
Counter (1) ·
Octal
Driver/Buffer (1) ·
Dual D-Type
Flip-Flop (1) ·
RJ45 Sockets (3) ·
Green LED Lamps
(8) ·
Red LED Lamps (8) ·
Quad XOR Gates (2) ·
8-Input OR Gate
(1) ·
Push-Button
Switches (2) ·
Switching Diodes
(2) ·
Piezo-electric Sounder
(1) ·
Resistor Network
(2) ·
Resistors and
Capacitors ·
Blank PCB (1) ·
Lab Text ·
Semiconductor Data
Sheets Circuit Description The circuit of the is
made up of the following sections: Cable
Driver and Monitor: This
section includes a clock oscillator, an 8-bit counter and the cable driver.
The counter cycles through all 8-bit combinations and feeds the INPUT end
of the cable under test. Fault
Detector: This section
is made up of XOR gates, fault indicator LED lamps, and an 8-input OR gate.
The circuitry catches and indicates any discrepancies between the data fed
into the cable and data received at the other end. Start/Stop
and Control Section: This
section is made up of a dual flip-flop, and resistor-diode OR gates. The
start/stop switches control the operation of the tester and are used to
reset the circuit to a starting state. Buzzer Circuit: This section is made up of
an astable oscillator and a speaker to provide the audible alert when a
fault is detected. Learning outcomes v Ethernet cabling specifications v Crossed and straight thru patch cords v Familiarity with the differential nature of
Ethernet signals on TP cables v Techniques of testing cables v Use of cable drivers v Using flip-flops as start/stop control devices v Astable oscillator circuit v 8-bit counters with start/stop enable gating v Use of XOR as an intelligent decision making
device ·
Build the
oscillator and the counter ·
Build the audio
circuit and test ·
Build the control
circuitry ·
Build the cable
driver and the monitor ·
Test with a TP
patch cord ·
Build the fault
detector circuit ·
Complete test with
a straight thru patch cord ·
Complete test with
a crossed patch cord ·
Find the fault
with a defective cable sample
