Circuit of cable tester with a separate LED Will show open circuits, short circuits, reversals, earth faults, continuity and all with four IC's. The circuit comprises transmitter and receiver, the cable under test linking the two. The transmitter is nothing more than a "LED chaser" the 4011 IC is wired as astable and clocks a 4017 decade counter divider. The 4017 is arranged so that on the 9th pulse,the count is reset. Each LED will light sequentially from LED 1 to LED 8 then back to LED 1 etc. As the 4017 has limited driving capabilities, then each output is buffered by a 4050. This provides sufficient current boost for long cables and the transmitter and receiver LED's. The receiver is simply 8 LED's with a common wire.
Skema rangkaian kabel (lan) tester
Pinning IC 4017
With a good cable and all wires connected then LED 1 will light at both cable ends, followed in sequence by LED 2 ,3, 4 etc to LED 8, the sequence then repeating. If a 4 wire cable is used, it must be connected to use the common. The sequence would be LED 1,2,3,4 repeating with a delay as the 4 unused outputs are stepped through. To check for earth contact faults, the probe labeled "to earth connection" would be physically connected to a local earth. A wire that is earthing will dim or extinguish the LED's at both ends of the cable. An LED not lighting at the receiver, indicates a broken or open circuit.
The LED sequence of course is stepped through, as you know the transmitter "pattern" it is easy to tell the state of the cable by viewing the receiver pattern. The earth condition will only show up if the contact to earth is less than 1000 ohms, a better but more time consuming method for earth faults is to use a meter on the Megaohms range.
The LED sequence of course is stepped through, as you know the transmitter "pattern" it is easy to tell the state of the cable by viewing the receiver pattern. The earth condition will only show up if the contact to earth is less than 1000 ohms, a better but more time consuming method for earth faults is to use a meter on the Megaohms range.
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