Monday, July 28, 2014

AC Live Line Detector

Good Morning everyone! Hope everyone is doing great! Now I'm going to post a very small diagram that can be used as an AC main line detector even if it is buried under plaster. 

So what do we need?

1. CD 4017  Decade Counter with 10 decoded outputs.
2. 0.1uF non-polar polyester type capacitor. (can be replaced with a 47uF electrolytic)
3. Red LED.
4. Single Pole Single Throw(SPST) Press Button.
5. Probe made of 5-20cm long, stiff insulated piece of wire. Can be used 15Amp cables for this.

Now the diagram!

Live Wire detector
How it works?

To understand how this circuit is going to work we have understand the purpose and action of the IC CD 4017. In simple word #14 pin is the input clock pin for this IC, when it gets a clock it starts counting which means it will give output to its 10 decoded output pins one by one. So a 100Hz clock will result in each output pins giving a 10Hz output. 

#3 is one of its output pins, you can use any other output pin.

#16 Pin is for supplying positive voltage and #8 is for negative or ground reference.

#15 pin is the RESET pin, we are keeping it low so that the counter keeps on counting.

#13 is for clock inhibit, we want to advance the count one step at the positive clock signal transition. For that we have to keep this pin at low. So we hook it up to the ground reference point.

If the probe is brought closer to a live wire, capacitive coupling between the live wire and the probe clocks the counter. and causes the LED to flash, and as I said earlier the any of the output pins will get only 1/10th portion of it(as it has 10 output pins so yes that's logical) so the LED will flash 5 times in the 50Hz 220V line and 6 times in the 60Hz 110V line.

Keeping it away from the Live wire will eventually lower or breaks the capacitive coupling and thus the counter will stop and the LED will turn off.

Making The Probe!

5-20cm long and stiff insulated piece of wire can be used. Usually those used in high current applications such as powering up an air-conditioner. Sensitivity of this circuit can be varied with the length of this probe.

Powering up the circuit

This circuit can run from 3V only, two AA sized battery can do this. And because of using 3V supply no need to use current limiting resistor with the LED.

It can work with up to 18V supply but going over 3.5/4V will require a current limiting resistor with the LED.

Hope it will help! Happy Experimenting.

CD 4017 Datasheet for more information.

Read my other posts here!

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