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 NXP Semiconductors


  • Live Line Detector

  • Created: Nov 03, 2014

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Summary

This circuit is a simple battery powered live line detector. The device effectively detects live ac mains without making any electrical contact with it. It uses 74HC4017D that is a 5-stage Johnson decade counter with 10 decoded outputs.It has an overriding asynchronous master reset input (MR) with wide supply voltage ranging from 2V to 6V.


Live-line detector has a capacitive coupling between the live conductor and the probe. It will clock the counter when around a live conductor causing the LED to flash 5 times per second in the 50Hz 220V line and 6 times in the 60Hz 110V line.It can occur due to the 74HC4017D IC that divides the mains 50Hz frequency by 10. When pin 14 (CP0) gets a clock, it will start counting to give 10 decoded outputs taken one at a time. A 100 Hz clock will result a frequency of 10 Hz in each output pins. The RESET pin is kept low so that the counter keeps on counting and the CP1 advances the count one step at the positive clock signal transition. Moreover, keeping it away from the live wire will eventually lower or break the capacitive coupling. Thus, the counter will stop and the LED will turn off.


This circuit can run from 3V only, two AA sized battery can do this. With the use of a 3V supply, there is no need to use current limiting resistor with the LED. It can work with up to 18V supply. However, voltage over 4V will require a current limiting resistor. The probe can be a stiff insulated piece of wire that is 5-20 cm long. To adjust the sensitivity of the circuit, the length of the probe can be varied. This device will be helpful in diagnosing a line whether it is live or not which is convenient to electricians to avoid fatal accidents.

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