A simple voltage detector with your own hands, schematic

Non-contact voltage detector with your own hands

When electricity is not handled properly, it leads to electrocution with a nasty experience. That’s why safety should come first when working with electricity. To avoid injury, you must first make sure that there is no AC voltage before you start working with an electrical unit such as an AC switchboard or power supply. It’s really hard to completely isolate the unit from the main power source; So, how can you be sure there is no voltage left?

Step 1:

There are several options available on the market and they vary in price, but if you don’t want to spend a lot and if you’re a true DIY enthusiast, this non-contact AC voltage detector is the right choice for you. After watching this video, you’ll be able to make your own AC tester for less than a dollar.

Step 2:

I’m going to show you 3 ways to make your own non-contact AC voltage detectors using: IC 4017 Decimal Number Counter 555 timer IC 3 x NPN general purpose transistors

Step 3:

I set out to do a review of the sensors most commonly used by the community in the design of various devices. Most of the sensors were not included in the series only because they will not be needed for my materials in the near future, but some are in the plans. I will definitely make a separate piece with acceleration, angular velocity, compass sensors and examples, so stay tuned for more articles!

All of these voltage detectors work on the simple principle of electromagnetic induction. A magnetic field is created around a conductor with current, and if the current through the conductor is alternating current (AC), the magnetic field created changes periodically. When we place an antenna near an AC object, a small current is induced into the antenna due to electromagnetic induction. By amplifying this current, we can illuminate an LED or buzzer circuit, indicating the presence of AC voltage.

Step 4: Tuning with the IC 4017

Picture

Let’s begin our discussion by assembling a circuit using an IC 4017. The IC 4017 is a 16-pin counter with a decimal number and is used for counting with a small range. It can count from 0 to 10 (number of decades) sequentially at a predetermined time and reset the count or hold it when needed. For this setup we will need: IC 4017, 2N2222 NPN general purpose transistor, 100 µF, capacitor, LED, 220 ohm, 1K resistor, buzzer, and a homemade antenna.

Step 5:

I set out to do a review of the sensors most commonly used by the community in the design of various devices. Most of the sensors were not included in the series only because they will not be needed for my materials in the near future, but some are in the plans. I will definitely make a separate piece with acceleration, angular velocity, compass sensors and examples, so stay tuned for more articles!

Connect pin 1 of the chip to the 1K resistor. The other end of the resistor connects to the base of the transistor. Then connect the pin collector to the -ve legs of the LED, the transistor, and the buzzer. The + ve legs connect to the + ve bus of the circuit board. The negative bus is connected to the emitter, pin 8, pin 13 and pin 15 of the chip. The antenna is connected to pin 14, which is the clock input pin. When the antenna receives the input clock pulses, it moves the counter and the LED flashes. You can connect the cable connected to pin 1 to either of the output pins of the chip. If you want, you can also connect 3 or 4 LEDs to the output pins to give it a chaser-like effect.

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Step 6: 4017 Demo

Picture

Now let’s do a quick test. When I move the live wire near the coil, the buzzer and the LED start flashing. But, as you can see, in some cases the LED and buzzer do not turn off even after I remove the wire. Also, this setting blinks when I put my fingers on the reel. Almost every other video on YouTube is made using this ultra-sensitive IC. But frankly, I’m not impressed with this setup.

Step 7: Tuning using the IC 555

Screenshot 4017 demo

In the second setup, I use the 555 timer IC. The 555 timer is the most common IC used in electronics projects because it is small, inexpensive, and very useful. This circuit is very simple. When the voltage on pin 2 drops below 1-3 VDC, the output on pin 3 becomes HIGH and the LED lights up. As long as this pin continues to remain low voltage, the OUT pin will remain HIGH. Thus, when the antenna detects a variable input, the output becomes HIGH and LOW and the LED flashes accordingly. For this setup we will need: IC 555, a 4.7 µF capacitor, an LED, 220 ohms, a 10K resistor, a buzzer, and a homemade antenna.

Step 8:

I set out to do a review of the sensors most commonly used by the community in the design of various devices. Most of the sensors were not included in the series only because they will not be needed for my materials in the near future, but some are in the plans. I will definitely make a separate piece with acceleration, angular velocity, compass sensors and examples, so stay tuned for more articles!

Connect pin 1 to ground. Pin 2 to the antenna. Pin 3 to the LED and the buzzer. Pin 6 to the + ve capacitor pin and pin 7 to one end of a 10K resistor. Then pin 6 or the threshold contact and pin 7 or the discharge contact should be connected to each other. Pin 8 and the other end of the 10K resistor are connected to the + ve bus on the PCB and finally connect all -ve branches to the negative bus on the PCB.

Step 9: 555 demo.

Picture

Okay, now let’s do a quick test. When we bring the live wire close to the antenna, the buzzer and LED start humming and flashing; and if I put my hand on the antenna, it will not affect the circuit. Which makes this setup more reliable because I don’t get any false readings.

Step 10: Tuning Using Transistors

Picture of 555 Demo

In the final setup, I use 3 2N2222 NPN general-purpose transistors. As you know, a transistor has three terminals – emitter, base and collector. The current from the collector to the emitter is controlled by the base current. When there is no base current, no current flows from the collector to the emitter. Thus, the transistor acts as a switch. Thus, the transistor can be ON, OFF, or intermediate. For this setup we will need: 3 x 2N2222 general purpose transistors, 1M, 100K and a 220 ohm resistor with LED buzzer and homemade antenna.

Step 11:

I set out to do a review of the sensors most commonly used by the community in the design of various devices. Most of the sensors were not included in the series only because they will not be needed for my materials in the near future, but some are in the plans. I will definitely make a separate piece with acceleration, angular velocity, compass sensors and examples, so stay tuned for more articles!

Connect the antenna to the base of the 1st transistor. The emitter is connected to the base of the 2nd transistor and coincides with the next one. Then connect a 1M resistor to the collector of the 1st transistor, 100k ohms for the 2nd and 220 ohms in series with the LED and buzzer. Then connect all resistors to the + ve bus of the circuit board. Finally ground the emitter of the 3rd transistor.

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Step 12: Demo Transistors

Picture

In this setup the antenna is connected to the base of the first transistor. When we bring the antenna close to an object under AC voltage, a small current is induced into the antenna due to electromagnetic induction. This current triggers the first transistor, and the output of the first transistor triggers the second and third transistors. The total gain (or ratio of collector current to base current) will then be a multiplication of three. The third transistor then turns on the LED and the buzzer circuit, indicating the presence of alternating voltage. Thus, the brightness of the LED is completely dependent on the base current. As the current increases, the brightness of the LED increases, giving a fading effect. You have to be very close to make this thing work. Maybe if I remove the antenna cover it will work well, but again this circuit failed to impress me.

Step 13: Soldering.

I really like the setup using the 555 IC timer. So, without wasting any time, let’s start soldering all the components on the board. I will start by soldering the base or socket of the IC. The IC socket is used as a chip filler. They are used to safely remove and install the ICs because the ICs can get damaged from heat during soldering. I then solder the 220 ohm resistor, LED and buzzer to pin 3 of the IC. After that I solder the 10K resistor and the capacitor to the board. When considering household appliances, your safety is the main goal. If you encounter big bills, flickering lights, and damaged appliances in your home, do one of these and make sure the home circuit is in proper working order. I then solder the 9V connector latch to the board. After soldering, I connect all the + ve and -ve pins according to the wiring diagram. Once everything is in place, it’s time for me to install the homemade antenna.

Step 14: Testing

Transistor Demo image

OK, now for the interesting part. Let’s see how this assembly works when a live wire is connected to it. Looks like I hit the jackpot. So, now you have no reason to blame the government energy system when you have bad wiring in our house. Go check it out now ….

Sensors and microcontrollers. Part 3. Measuring current and voltage

We move on to the final part of the sensor review series, in which we will look at DC and AC current and voltage sensors. For all the other sensors that didn’t make it into the main series, we will do additional reviews when we need them in future articles. This article opens a new series of materials about measuring power quality parameters, which will include the connection of current and voltage sensors to the microcontroller, consideration of the algorithms of power quality analyzers, the meaning of certain power quality indicators and what they mean. Besides we will touch upon the topic of digitization and data accuracy, that many people care about, and that was mentioned in the comments to the first article.

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Synopsis of

Part 1. The Math. Here we consider the sensor not connected to any particular measured parameter. The static and dynamic characteristics of the sensor are considered. Part 2. Climate control sensors. It deals with temperature, humidity, pressure, and gas composition sensors Part 3. Sensors for electrical quantities. In this part I will look at current and voltage sensors

There is direct current, there is alternating current. It can be all at once, which sometimes causes a lot of problems. But more about that later. First, let’s understand the terminology. Figure 1: Voltage in AC Circuits When we measure AC current, we have 4 different quantities to guide our measurements. All of the following formulas and terms apply to the current meter as well. 1. Instantaneous voltage value is the potential difference between two points. Measured at a certain point in time. This value is the base value in all other calculations. In fact, our task will be to read a successive set of instantaneous voltage values at equal intervals of time, in order to subsequently use them to obtain some other data. u = u(t) (1) We obtain approximately the following graph: Figure 2: Measurement of a series of instantaneous voltage values When selecting the frequency of the sensors we are guided by the Kotelnikov-Shannon theorem, when in order to recover a signal with frequency f we need to read out a frequency greater than 2f. I note the necessity of strict inequality, i.e. if we need to digitize a signal with frequency 50 Hz, it is necessary to read with frequency not less than 101 Hz. But, of course, the more the better. If you remember GOST for power quality indicators, then in the Harmonics section we will find that the harmonics up to 40, i.e. up to 2 kHz are interesting for our measurement. And the electricity meter chips make a reading with a frequency of 4096 times per second. The degree of two is chosen so that fast Fourier transform algorithms can be applied. Having this large data set collected in a unit of time such as 1s move on to the following: 2. The amplitude value of the voltage – which is defined as the maximum modulo value from our sample: (2) where [u(t)] is the data array. For harmonic oscillations, this value is used in the following formula: (3) 3. The mean value of the voltage, i.e., the arithmetic mean, i.e., the constant component of the alternating voltage. (4) Where is the sampling period of the analog signal. I intentionally write the sum instead of the integral. In an industrial AC network, the average value must be zero. If this condition is not met, there may be some problems, because the direct current magnetizes the transformers, bringing them into saturation, or heats up the supply line. The latter by the way can be useful to solve the problem of frozen ice on wires – the wire is heated and the ice comes off. In low-current analog circuits, the constant component is present all over the place and can be very useful. And if it gets in our way, we quickly get rid of it, but more on that later. 4. The rms voltage . – also known as the rms value of the voltage – on a linear active load it does the same work as a constant voltage of the same level. It is determined by the following formula: (5) When measuring the voltage at the outlet, we are usually interested in this very effective voltage, which is 230/380V. The amplitude and effective values of the sinusoidal voltage are related by . When designing the measuring system we will be primarily interested in the amplitude value of voltage and current.

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During the measurements we will be guided by one of the following schemes: Figure 3: Wiring the Measuring Devices A riddle to the mind – both wiring diagrams are correct, but under what circumstances is it important to choose the right one? The answers are in the comments.

Voltage gauges.

The first thing to do is to make a voltage measurement. All of the following applies to voltages at least as high as the supply voltage of the ADC of our controller. So we need to measure voltage with an amplitude greater than the ADC can chew. Therefore, the voltage level must be lowered – i.e. the signal must be attenuated. For small voltages (like the thermocouple thermoelectric emf from the last article) we need the inverse problem – signal amplification. This is a more complicated problem and we will definitely return to it in the next articles. Let’s set the condition for the calculation of our sensors: Measurement voltage: AC, 0-1000V, frequency 50/60Hz. For a three-phase voltage of 380V the amplitude is almost 600V, but there are also 660V networks. So let it be. Actually I took this calculation from my iron and I’m too lazy to redo it. Output voltage ± 1,65V is half of +3,3V
  • Voltage divider
  • Wide range of voltages and frequencies, determined by the nominal resistors;
  • High accuracy, again determined by the accuracy and thermal stability of the resistors;
  • Measures DC and AC voltages
  • no galvanic isolation – when interacting with an industrial network it is necessary to provide protection for the user from electric circuits, or to use galvanic isolation;
Low efficiency – all the current of the divider goes into heat;
  • Voltage transformer
  • A huge range of operating voltages – up to hundreds of kilovolts and higher;
  • much needed galvanic isolation.
  • Operates on a specific frequency bandwidth;
Operates only with AC voltages;

Electronic isolated sensor

The disadvantages of both circuits are deprived of the electronic isolated sensor. In fact, it is a complete device. There is a voltage divider, operational amplifiers, galvanic isolator and a scheme of isolated power supply for all this mess. Figure 9: Electronic isolated sensor schematic diagram I have seen only industrial sensors with 0-10V voltage or 0-10mA current output. Unlike previous sensors it produces a unipolar signal. Basically, you could design such a circuit yourself using, for example, an isolated analog amplifier like the HCPL-7850. The main drawback of this circuit is that it is very complicated and very expensive. And as Mr. progchip666 rightly points out in the comments

  • To transmit an analog signal with even one percent accuracy over a galvanically isolated interface is extremely difficult, so often in this case you have to convert it to digital and in this form already converted. Unfortunately, the amplifier shown in the schematic has to be powered as well. Of course from a galvanically isolated source.
  • galvanic isolation;
  • high accuracy;
  • High accuracy, again determined by the accuracy and thermal stability of the resistors;
  • measures DC and AC voltages.
  • expensive;
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complicated circuitry.
Additional references
Current Sensors
  • galvanic isolation;
  • high accuracy;
  • wide range of voltages and frequencies;
  • Measures direct and alternating currents.
  • no galvanic isolation;
low efficiency.
  • To transmit an analog signal with even one percent accuracy over a galvanically isolated interface is extremely difficult, so often in this case you have to convert it to digital and in this form already converted. Unfortunately, the amplifier shown in the schematic has to be powered as well. Of course from a galvanically isolated source.
  • galvanic isolation;
  • operation with large currents of thousands of amperes;
  • measures only AC current in a certain frequency range (except Rogowski coil);
Changes the phase of the signal and requires compensation
  • Hall-effect current sensors
  • AC sensor ACS712 measures dc and ac currents up to 30A with an accuracy of ±1.5%
  • ACS713 sensor – optimized for dc currents up to 30A. Has twice the sensitivity of its universal counterpart.
  • AC and DC probe ACS754 – measures DC and AC currents up to 200A with ± 1.5% accuracy
  • ACS755 sensor – optimized for direct current measurement.
  • ACS756 sensor – sensor for measuring DC and AC currents up to 100A with a supply voltage of 3-5V.
  • wide range of voltages and frequencies;
  • Measures direct and alternating currents.
  • galvanic isolation
Expensive
Additional references:

Conclusion

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