The purpose of this litle circuit was to go/no-go test a quantity of CAT5 cables and provide some indication of floor wiring (data jack to switch port) via the path & punchdown panesl. It will indicate a crossed pair or an open pair and a short across pairs. It is not intended as any other type of tester, there are plenty of commercial units for that.

IC1 is a 555 timer IC connected in astable mode. Output pulses appear at pin 3 to trigger IC2, a CD4017 decade counter. The 555 output with the components specified provides one pulse per second. For each pulse at pin 14, the decade counter sets the next output pin high. Only one output is high at any one time. After 4 pulses, the next decade output (pin 10) resets the decade counter via pin 15, and the next pulse sets the first output high once more. In this way we get a repetitive sequence from the 4017 on pins3, then 2, then 4, then 7, then reset.

These outputs pins are connected to the RJ45 socket, so that a pulse is sent down one leg of each wire-pair in turn.
The return legs are connected to 0 volts via LEDs showing the current flow in each pair.

1. Component values are not critical, they only affect the speed of the sequence.
2. The circuit is wired for 586B compliant cables, 586A would change the sequence of LEDS 2 & 3.
3. Practical unit built on stripboard (veroboard), not pcb.
4. for more details on cables.

If you have any questions or are in need of other additional information in regards to the above circuit, please contact Paul Hancock here.
This project is copyright © by Paul Hancock.

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Project Copyright © 2002 - by Paul Hancock