Contactless Voltage Detector

When electricity is not properly handled, it results in electrical shocks with nasty experiences, which is why safety must come first when working with electricity or electrical devices. In order to avoid injury prior to starting your work on an electrical box such as an AC main switchboard or a power supply, you must first verify that there is no AC voltage. It is really hard to completely isolate a device from the main supply. So how can you be sure that there is no voltage remaining? There are several options available in the market and they range in price. But if you don't want to spend a lot and if you are a true DIY lover, this non-contact AC voltage detector is the right choice for you. After watching this video, you should be able to make your own AC tester for less than a dollar. In this video, I'm going to show you three ways of making your own contactless AC voltage detector using IC4017 decade counter, 555 timer IC and three general purpose NPN transistors. All these voltage detectors work on a simple principle of electromagnetic induction. A magnetic field is produced around a current carrying conductor and if current through the conductor is alternating current, the magnetic field produced varies periodically. When we place an antenna near an AC energized object, a small current gets induced into the antenna due to the electromagnetic induction. By amplifying this current, we can light up an LED or a buzzer circuit indicating that the AC voltage is present. Let's start our discussion by assembling the circuit using the 4017 IC. 4017 is a 16 pin decade counter. It is used for low range counting applications. It can count from 0 to 10 sequentially in a predefined time and reset the count or hold For this setup, we need a 4017 IC, a general purpose NPN transistor, 100 microfarad capacitor, LED, a 220 ohm and a 1k resistor, a buzzer and a homemade antenna. Connect pin number one of the IC to the 1k resistor. The other end of the resistor connects to the base of the transistor. Next, connect the collector pin to the negative legs of the LED transistor and the buzzer. The positive legs connect to the positive rail of the circuit board. The negative rail connects to the pin number eight, pin number 13 and pin number 15 of the IC. The antenna is connected to pin number 14 which is the clock input pin. When the antenna receives input clock pulse, it advances the counter and the LED flashes. You can connect the cable connected to pin number one to any one of the output pins of the IC. If you want, you can also connect three to four LEDs to the output pin to give it a chaser like effect. Now let's do a quick test. Moving a live wire close to the coil makes the buzzer and the LED to flash. But as you can see, at some instances, the LED and the buzzer won't go off even after moving the wire away. Also, this setup flashes when I put my finger around the coil. Pretty much every second video on YouTube is made using this hypersensitive IC. But frankly speaking, I'm not impressed by this setup. In the second setup, I'm using the 555 timer IC. 555 timer is the most common chip used in DIY electronic projects because it's small, inexpensive and very useful. For this setup, we need a 555 timer IC, 4.7 microfarad capacitor, LED, 220 ohm and a 10k resistor, buzzer and a homemade antenna. Connect pin number one to ground, pin two to the antenna, pin three to the LED and the buzzer, pin six to the positive leg of the capacitor and pin seven to one end of the 10k resistor. Then pin six or the threshold pin and pin seven or the discharge pin need to be connected to each other. Pin number eight and the other end of the 10k resistor connects to the positive rail of the circuit board and finally connect all the negative legs to the negative rail of the circuit board. This circuit is very simple. When the voltage on pin two falls below one third of the VCC, the output on pin three goes high and the LED lights up. So, when the antenna detects an alternating input, the output goes high and low and the LED flashes accordingly. As we bring a live wire close to the antenna, the buzzer and the LED starts buzzing and flashing and if I put my hand around the antenna, it has no effect on the circuit which makes this setup more reliable as I'm not getting any false readings. In the final setup, I'm using three general purpose NPN transistors. As we know, a transistor has three terminals, emitter, base and collector. Collector to emitter current is controlled by the base current. When there is no base current, no current flows through the collector to emitter. Thus, a transistor acts like a switch. So, a transistor can either be on, off or in between. For this setup, we need three 2N2222 general purpose transistors, one 1Meg, one 100K and a 220 ohm resistor, LED, buzzer and a homemade antenna. Connect the antenna to the base of the first transistor. The emitter connects to the base of the second transistor and the same with the next one. Then connect the 1Meg resistor to the collector of the first transistor, 100K to the second and 220 ohm in series with the LED and the buzzer. Then connect all the resistors to the positive rail of the circuit board and finally ground the emitter of the third transistor. When we move the antenna close to an AC energized object, a small current get induced into the antenna due to the electromagnetic induction. This current triggers the first transistor and output of the first transistor triggers the second and the third. The total gain or the ratio of the collector to the base current would then be the multiplication of the three. The third transistor then turns on the LED and the buzzer circuit indicating the presence of AC voltage. So the brightness of the LED totally depends on the base current. As the flow increases, the LED's brightness goes high giving it a fading effect. One thing to note is you have to be really up close to the wire to get this thing to work. Maybe if I take the antenna's cover off, it will perform well but again this circuit was not able to impress me at all. I don't know about you but I really like the setup using the 555 timer IC. So without wasting time let's solder all the components to the circuit board. I'll start by soldering the base or the socket of the IC. An IC socket is used as a placeholder for ICs. They are used in order to allow safe removal and insertion of ICs because IC chips may get damaged from heat while soldering. Next I'm soldering the 220 ohm resistor, LED and the buzzer to pin number 3 of the IC. After that I'm soldering the 10k resistor and the capacitor to the board. When considering household electrical appliances, your safety is the main goal. If you're facing high bills, flickering lights and damaged appliances at your home, go ahead and make one of these to make sure that your home circuit is in proper working condition. Next I'm soldering the 9 volt battery snap-on connector cable to the plate. Once soldered, I'm connecting all the positive and the negative pins as per the circuit diagram. Once everything is in place, it's time for me to install the homemade antenna. Okay, now the interesting bit. Let's check out how this assembly works when I bring a live wire next to it. Looks like I've hit the jackpot. So, now you have no reason to blame the nation's power system when you have a poor wiring inside your home. Go ahead and check it now. Thanks again for watching this video. I hope it helps you. 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