This document describes a simple computer network lead tester project that uses LEDs and integrated circuits to check if network leads are correctly wired. The tester connects each wire in a network lead to an LED. The LEDs will light up in sequence if the lead is wired correctly. If an LED fails to light or they light in the wrong order, it indicates an incorrect wiring. The circuit uses a 555 timer and 4017 counter IC to sequentially activate the LEDs. A stripboard layout and circuit diagram are provided to construct the tester.

1. Computer Network Lead Tester Project
This project was designed for confirming the continuity and correct wiring of computer network leads
which have 8 wires, but it can be used to check any lead with up to 8 wires by using appropriate
connectors. For example stereo audio leads with 5-pin DIN plugs can be checked by just using the first 5
LEDs. The tester is simple but it can save a great deal of time when making up leads and it is much
cheaper than the more sophisticated alternatives!
The tester works by connecting each wire to an output at one end and an LED at the other end. The
outputs are switched on one at a time in sequence so that a correctly wired lead will make each LED light
in turn. The 4017 IC counts up to 10 so there is a pause (for the 9th and 10th counts) before the LED
sequence repeats. If the LEDs light up in the wrong sequence one (or both) of the connectors is wired
wrongly. If an LED fails to light it indicates a broken connection. Please note that the RJ45 computer
network plugs cannot normally be re-wired, instead they must be cut off and replaced.
Parts Required
•
•
•
•
•
•
resistors: 2.2k, 22k, 180k, 560 ×8
• 555 timer IC
capacitors: 0.1µF, 1µF 16V radial ×2
• 4017 counter IC
red LEDs ×8
• DIL sockets for ICs: 8-pin, 16-pin
push switch
• battery clip for 9V PP3
stripboard: 16 rows × 19 holes
RJ45 computer network sockets ×2 (a dual socket for example)
(or choose suitable connectors for the leads you wish to test)
555
Stripboard Layout
2k2
0.1µF
red
180k
1µF
Press to
to test
red
560
560
560
560
560
560
560
560
red
1µF
22k
5
6
2
1
3
7
8
4
8 wires to the
network lead socket
then to LED anodes
(the numbers show
the LED sequence)
black
to LED cathodes (0V)
4017
cut the track under
each 560 resistor
Each socket should be wired up in the
same way, so that wire 1 from the
stripboard connects to pin 1 on the first
socket, and pin 1 on the second socket
connects to LED 1.
= cut track
to stripboard (see above)
1 wire
socket
8 wires
Network lead
being tested
8 wires
0V wire to LED cathodes
8 wires to
LED anodes
(long leads)
LEDs mounted on case
socket
Circuit diagram
1µF
2k2
7
4
8
6
2
180k
0.1µF
555
timer
16
4017 1-of-10 counter
14
15
1
3
8 13 3
2
4
7
10
1
5
6
8x
560
+
8-way lead is connected in here
1µF
1
2
3
4
5
6
7
8
If the lead is OK each LED should light up in
sequence from left to right (1 to 8 above).
THE
ELECTRONICS
CLUB
+
© John Hewes 2006, The Electronics Club,
www.kpsec.freeuk.com
A kit for this project is available from
RSH Electronics
22k
9V