Voltage indicator 12. Voltage indicator, types, functions, instructions for use. DC Voltage Check

The device is an LED voltmeter (voltage indicator) of a 12V battery, using the well-known LM3914 microcircuit (datasheet).

I needed this device so that I knew when the car battery was fully charged from charger. Because The charger was of an old type and did not have any dial or digital indicators for measuring voltage.

For the LED bar indicator (bar), I chose HDSP-4832 with 10 LEDs of three different colors: three red, four yellow and three green.

To correctly indicate voltage, you need to determine the lower and upper levels of the measured voltages, so that the first and last LEDs (strips) on the indicator light up at these levels, respectively.

For 12V car battery, the following ranges were selected: the first LED lit up at a voltage of 10V, and the last at a voltage of 13.5V, i.e. The voltage indication step was 0.35V per LED. Naturally, you can set other voltages using two trim resistors. This makes it possible to use this indicator to measure voltage, for example NiCd or NiMH batteries. The voltage limits in this case are set to V min = 0.9 * N cells and V max = 1.45 * N cells, where N cells is the number of battery “cans”. Plus, between the + and - batteries, a powerful resistor rated for a current of at least 0.5A must be placed to simulate a real load.

The LM3914 chip can operate in two modes: “dot” mode, in which only one LED lights up, and “bar” mode, in which several LEDs light up in increasing order. This scheme operates in “bar” mode; for this purpose, pin 9 of the microcircuit is connected to the plus of the power source.

When operating in bar mode, the power consumption of the LM3914 increases accordingly. When all 10 LED segments are lit, the LM3914 consumes almost 10 times more than if only one LED (segment) was lit. To prevent burnout of the LM3914 m/s, it is necessary to ensure that the LED current does not exceed the maximum permissible.

The maximum power dissipation of the microcircuit should not exceed 1365 mW. And if we assume that the maximum input voltage is 14.4V, then the maximum possible current will be I = P/V = 1.365/14.4 = 94.8mA. That. the current of each indicator segment should not exceed 94.8/10=9.5mA. In the circuit, the resistance of resistor R3 (4.7 kOhm) sets the maximum current of the LEDs. The LED current is approximately 10 times greater than the current that passes through this resistor I R3 = 1.25 / 4700 = 266 μA. That. The current per LED is limited to 2.6 mA, which is much less than permissible.

Input stage: to take readings of the input voltage (and it also powers the circuit), the circuit uses a 1:2 voltage divider connected to pin 5 of the microcircuit. The divider consists of two resistors with a nominal value of 10 kOhm, etc. the voltage taken from the divider is in the range from 5V to 6.75V, while the input voltage will be from 10V to 13.5V. These same values ​​will be used to calibrate the LM3914.

Schematic diagram of the indicator

The circuit consists of two elements: a separate control circuit and a separate indicator board. They are connected to each other using an 11-pin connector.

The main defining elements of the circuit:
R1 and R2 - voltage divider
R3 and R4 - limiting the LED current and setting the upper voltage limit
R5 - setting the lower voltage limit

I talked about R1, R2 and R3 above. Now let's look at R4, which sets the upper threshold (output 6 m/s):
At pins 6 and 7 of the microcircuit, it is necessary to set the voltage to 6.75V (which is the input voltage of 13.5V after the divider, if the battery is fully charged). Knowing the value of the current passing through R3, and also adding here the “error current” current from pin 8 of the microcircuit (120 μA), we can calculate the resistance of R4:
6.75V = 1.25V + R4(120uA+266uA)<=>
R4 = (6.75 - 1.25)/(386uA)<=>
R4 = 14.2 kOhm or more (we choose a 22 kOhm trimmer resistor)
With a 22 kOhm trimmer resistor, we can adjust the voltage on pin 7 in the range from 1.25V to 9.74V, which makes it possible to set the upper voltage limit from 2.5V to 19.5V.

Resistance R5 sets the lower voltage limit:
Substituting the following values ​​into the formula V O = V I * R B /(R A + R B):
R A = 10 * 1K internal resistors LM3914
R B = R5
V I = upper voltage limit 6.75V
VO = lower voltage limit 5V
we get:
5 = 6.75 * R5/(R5 + 10K)
R5 = 28.5K or more (we choose a 100kOhm trim resistor)

PCB

As mentioned above, the device consists of two components; accordingly, 2 different printed circuit boards are used. This makes it possible to use remote display, for example on a car panel.

There was only one jumper on the printed circuit board (marked in red).

Download the project in and printed circuit boards you can below

List of radioelements

When carrying out even the most basic work with electricity, it is important to follow safety precautions. Even with extensive experience in in this direction There is no point in taking the risk, as it is life-threatening. To check availability electric current, it is necessary to always have a voltage indicator on the farm. The main advantage of this device is its ease of use and instant determination of the presence of current in the network.

If you look at the photo of the voltage indicator, you can see that this tool is a screwdriver with a built-in indicator.

Manufacturers offer a lot various types indicators, but each has its own operating principle. Before use, you need to understand the rules and avoid mistakes.

Types of indicators

Screwdriver

The simplest and most common is a passive screwdriver indicator. With its help you can find out whether there is voltage in the circuit or not. The main advantage of this type of screwdriver is that the indicator shows the presence or absence of voltage after touching the contact.

There is a contact on the handle that must be clamped when we bring it to the conductor. The result of the current is shown by a neon lamp built into the handle.

Electricians rarely use this type of mains voltage indicator due to its low functionality. This type of indicator is more suitable for home use.

Active screwdriver

A more advanced indicator model is the active screwdriver. This type of screwdriver determines the presence of voltage in the network, as well as its integrity. The case contains a battery-powered circuit and an LED.

The main feature of this indicator is the possibility of contact and non-contact use, and is suitable for professional use.

Control

The most popular tester among electricians is a do-it-yourself voltage indicator - control. This is a design in the form of a light bulb inserted into a socket and wires, the edges of which are probes.

The control is convenient because it shows the presence of voltage and whether the power of the network is normal. The main advantage of this indicator is the ability to test three-phase circuits.

Multimeter

Another type of voltage indicator is a multimeter. This is a universal device that measures current, voltage, frequency, capacitance, etc. The multimeter measures to the nearest thousandths.

Universal probe

For professional use, electricians often choose a universal probe. This device is more multifunctional than the others. Thanks to the ability to determine phases, pros and cons, call, etc. This indicator is considered one of the main tools of an electrician.

Non-contact voltage indicator

A non-contact voltage indicator is also considered one of the safest. This type The indicators are equipped with three operating modes. This is non-contact use with high and low sensitivity and light notification. These three modes vary depending on the tasks being performed:

• Light notification - a signal is given by the glow of a light bulb. Detects the presence of current only upon contact.
• Non-contact notification with low sensitivity - the device detects the presence of current at a short distance.

Non-contact alert with high sensitivity – detects the presence of current over a long distance. This mode allows you to measure the voltage in wires plastered in the wall, as well as identify their route.

This screwdriver is a simplified multimeter. This is an excellent device with many functions and very easy to use. With its help, you can check the integrity of the circuit, determine the voltage at a distance, and also have light and sound indication.

To obtain more information about the electrical circuit, use a digital voltage indicator. This indicator on the display provides more detailed information by showing the digital value of the network voltage. With its help, you can control the voltage by setting maximum and minimum values. This device is installed to protect against voltage surges.

When choosing an indicator, it is important to know all the pros and cons. It is recommended to carry out work related to electricity with extreme caution and check the presence of electricity in the network only using indicators.

Photo of voltage indicator

A very necessary tool in the household, which must be present in every apartment or house. Surely, in the life of every person, such a situation has happened when suddenly, for unknown reasons, the lights went out. The first reaction of any person is confusion, and in some cases even panic. What happened, where is the light, where did the electricity go, what to do now and what to do? After some time, thoughts about the following content come to mind: I wonder if it’s just me who lost the light or everywhere?

With the right approach to the matter, answers to all these questions can easily be given by voltage indicator. With its help, you can easily determine the presence of or or on the switch. And also, establish the presence or absence of voltage on the input circuit breaker and the electricity meter.

In this article, we will get acquainted with the most common types of voltage indicators in everyday life, analyze visual methods of working with each of them, the pros and cons, and also summarize for each of the options regarding ease of use in everyday life.

Nowadays the electrical equipment market offers a huge variety of various types voltage indicators, which one to choose and how not to make a mistake with the purchase? Let's figure it out.

In this article we will look at the main types of voltage indicators,

Indicator screwdriver - voltage indicator with light warning, contact type

This voltage indicator has one function, determining the presence or absence of voltage on a wire or contact of electrical equipment.

This type of pointer has two working parts. The first has the shape of a flat screwdriver and comes into direct contact with a live element of the electrical wiring.

The second part is located on the handle of the indicator screwdriver and is necessary to create resistance.

Let's check this indicator in operation

Let's look at the use of this screwdriver using a specific example. We have a phase wire connected to one contact and a neutral wire to the other. The voltage indicator will indicate which wire the phase is on.

To determine, we hold the contact located on the handle of the voltage indicator with our thumb and alternately bring the working part of the indicator first to one, then to the other contact circuit breaker. Thumb At the same time, he must be naked, without gloves.

If there is voltage on the contact, the pointer indicator will show it, a weak red or orange light inside the screwdriver will light up. But on the zero contact (in our example the blue wire goes to it), the indicator will not show anything.

Let's summarize the testing results

Pros:

• does not have batteries, operates directly from the phase;
• due to its simple design, it has high accuracy and reliability;
• it is possible, if absolutely necessary, to use the voltage indicator as a flat-head screwdriver;
• easy to operate;
• service life is not limited;
• remains operational under any temperature conditions environment.

Cons:

• very weak voltage indicator light, very difficult to see in the sun;
• To work with the indicator you have to take off your protective gloves.

We conclude: A very simple and reliable voltage indicator, ideal for indoor work.

Indicator screwdriver - voltage indicator, with the function of contact and non-contact use, with light notification

This type of voltage indicator has two functions. Determination of the presence and absence of voltage (phase) by contact and non-contact methods, as well as the function of checking the integrity of the circuit (wire, cable, fuse).

The index has two working parts. The first one looks like a flat screwdriver. Designed for direct contact with live elements.

The second is intended for non-contact determination of the presence of voltage, as well as for determining the integrity of the circuit in conjunction with the first part.

Inside the insulated transparent handle of the voltage indicator there is an LED light bulb, which, when interacting with a phase, signals its presence. It also contains batteries, LR44, 157, A76 or V13GA batteries.

Let's check this indicator screwdriver in operation.

We alternately bring the first working part of the voltage indicator to the contacts of the two-pole circuit breaker. First to one, then to the other. At the zero contact the indicator showed nothing.

On the phase one, the voltage indicator light came on, signaling the presence of voltage (phase) at this contact.

Also, using this voltage indicator, you can determine the presence of a phase using a non-contact method; for this we will use the second working part.

It is worth noting that for this voltage indicator to work correctly, it must be held correctly. This must be done, as shown in the figure below, by the middle of the screwdriver body, without touching the first working part with your hand, otherwise the pointer may operate in the “dialing” mode, thereby giving a false signal about the presence of a phase.

We bring the indicator screwdriver with the second working part to the wire insulation; it is not necessary to touch it; the indicator will begin to signal the presence of a phase already at some distance from the wire.

The function of checking the continuity of the circuit (continuity) works simply.

Attention! All manipulations to check the integrity (continuity) of a wire, cable or various types of fuses are carried out only with the voltage turned off.

Sequence of actions in dialing mode

Let's say we need to test the integrity of one wire strand. To do this, we carry out the following series of actions.

• take off the gloves;
• we pinch the second (back) part of the voltage indicator with a bare finger, say the right hand;
• With the first working part (made for a flat-head screwdriver) of the voltage indicator, we touch one end of the core of the wire being tested;
• The second end of the wire being tested must be touched with the fingers of your left hand.

Now let's look:

• If the voltage indicator lamp lights up, the wire being tested is intact.
• If the indicator light does not light up, the core is damaged and is in a clean break.

Fuses are also checked in a similar way.

Pros and cons of this indicator screwdriver

Pros:

• bright indicator light;
• the possibility of contact and non-contact use to determine the presence or absence of a phase;
• there is a function for checking the continuity of the circuit (continuity);
• If necessary, it is possible to use the pointer as a flat-head screwdriver.

Cons:

• the need to periodically replace batteries;
• ambient temperature limitation from -10 to +50 degrees Celsius.

We conclude: A reliable and understandable voltage indicator, it has the functions of checking circuit integrity and without contact determining the presence of voltage.

Suitable for both home and professional use.

Digital indicator screwdriver, with contact and non-contact voltage detection functions

This voltage indicator does not have any power supply.

On its body there is a window with a liquid crystal display, which displays digital voltage values ​​of 12, 36, 55, 110, 220 Volts.

There are also two pole buttons. The first is designed for non-contact voltage measurement.

The second is for contact measurement.

The indicator has one working part, made in the form of a flat screwdriver.

Let's check the voltage indicator in operation

First of all, we will test the contact measurement method. We bring the indicator to the first, zero contact of the circuit breaker. A value of 55 V appears on the indicator display.

A small voltage may indeed be present on the neutral wire, but as a rule, it is only observed under loads (working electrical equipment). Our machine was turned off at the time of measurements, that is, there was no actual load.

Now, bring the indicator to the phase contact.

The indicator clearly showed 110 Volts. The real voltage value of 220 V on the indicator display appeared barely visible.

Attempts to make the voltage indicator work in non-contact mode were unsuccessful, but a function not stated in the digital indicator’s instruction manual was identified: if you touch a phase without pressing the buttons, the indicator shows a barely visible lightning bolt on the display, indicating the presence of voltage.

Let us summarize the results of testing this voltage indicator:

Pros:

• does not have a power source;
• shows approximate digital voltage values.

Cons:

• The non-contact voltage detection function declared by the manufacturer does not work;
• ambient temperature restrictions from -10 to +50 degrees Celsius;
• has limitations on the measured voltage of 250 V;
• According to the instructions, it is forbidden to touch two buttons at once ( can probably give you an electric shock).

We conclude: This indicator is very unreliable in operation.

Voltage indicator with non-contact, sound and contact light indication functions

This indicator, unlike its competitors presented above, in addition to a light warning, also has an audible warning. This feature makes this device very safe in detecting the presence or absence of voltage.

On this indicator, the non-contact mode for detecting the presence of voltage has a sound alert, and it is accompanied by a green light indication.

Contact mode has only a light warning, accompanied by a red indication.

For this purpose, the device has two LED lights.

There is a speaker for sound.

At the end of the pointer there is an operating mode switch:

1. "O" - contact light warning function, accompanied by the glow of a red light, detects the presence of voltage only in direct contact with the phase;
2. "L" - non-contact sound notification function of medium sensitivity, accompanied by the glow of a green light, detects voltage from short distance, even through double insulation of the wire;
3. “H” is a sound notification function of maximum sensitivity, accompanied by the glow of a green light, detects the presence of voltage from a long distance through the wire insulation.

The working part, hidden under a protective cap, is made in the form of a flat-head screwdriver.

There is a special contact at the end of the voltage indicator, which, in conjunction with the main working part of the device, is used to determine the integrity of the circuit. The so-called “dialing” mode.

Sequence of work in the "dialing" mode:

• take off the gloves;
• press the end contact of the voltage indicator with the finger of your right hand;
• then, with the main working part (made for a flat-head screwdriver), we touch one end of the core of the wire being tested;
• You must touch the second end of the wire with the fingers of your left hand.

If the chain is complete, then:

• in "O" mode - the red light will light up;
• in “L” and “H” modes - the green light will light, accompanied by a sound signal;

If the chain is damaged:

• The indicator will not respond in any of the modes.

Let's check the pointer in action

We turn on the contact indication mode - “O”.

Now, one by one, we bring the voltage indicator first to the zero contact of the circuit breaker, where it does not show anything, as expected.

Then, to the phase contact. The voltage indicator light comes on.

We move on to the non-contact mode of medium sound and light indication “L”.

This mode can work both with the bare working part of the pointer and with a protected cap. So, turn on the mode and move the pointer to the circuit breaker. No need to touch contacts! We keep the device at a distance of 1-2 cm from live parts. Near the zero contact, the pointer indicators are silent, and near the phase contact they begin to emit a sound and light warning, and a green light comes on.

We test the device in the last position of the switch - “H”, the mode of increased sensitivity of non-contact sound and light indication.

You can use this mode with the cap on or off. We turn on the device and bring it to the circuit breaker.

The indicator turns on a sound and light alert when a phase is detected on one of the wires or cables already 20 centimeters before the contacts of the circuit breaker.

Let us summarize the testing of this voltage indicator

Pros:

• a wide range of functions, three display modes, one light and two sound;
• the ability to determine voltage at a distance;
• non-contact light indication is duplicated by sound;
• There is a circuit continuity check function.

Cons:

• The device runs on LR44, 157, A76 or V13GA batteries, which run out quite quickly. Before carrying out work, a preliminary check of the functionality of the device is required;
• operating ambient temperature from -10 to +50 degrees Celsius.

Conclusion: An excellent, understandable and adequate device, with a wide range of functions. Suitable for both professionals and beginners.

Double-pole voltage indicator, two-pin type, with voltage detection function

This voltage indicator belongs to the professional category. Unlike conventional single-pole indicators, it cannot determine which of the contacts the phase is on, but can notify the presence of voltage in general.

This device consists of two probes, at the end of each of which there is a working part made in the form of sharp pins, the probes connected to each other by a soft copper wire.

One of them has an indicator scale with stepped voltage values ​​6, 12, 24, 50, 110, 120 and 380 Volts printed on it.

By making measurements using a two-pole indicator, the device will show in which range the measured voltage is located. Can be used in a 380 Volt network.

The only indicator capable of accurately determining a specific network voltage of 220 or 380 Volts, as well as identifying 220 Volts in the network.

The device has two working parts.

The first is made in the form of a sharp probe located on the main body of the device.

The second one is located on the additional body; its working part also looks like a sharp probe.

Let's check the bipolar voltage indicator in operation

To operate the device, you need two contacts, phase and zero or phase and ground. We touch the phase contact with one working element, and the neutral or ground contact with the other. In our example, on a two-pole circuit breaker there is a phase and a zero. We touch the contacts of the circuit breaker with the working parts of the device. We insert the probe of the main part into one contact, and the probe of the additional part into another.

If there is voltage on the machine, the indicator lamps begin to glow. The scale of the main part of the indicator displays a value equal to the mains voltage. In our example, the display shows a voltage of 220 Volts, which corresponds to reality.

Let's summarize the results of testing a two-pole voltage indicator

Pros:

• has a step scale for determining voltage;
• has the ability to work in a network of 220 and 380 Volts;
• is able to detect overvoltage in a 220 Volt network;
• does not have electrical power elements;

Cons:

• weak point: flexible wire connection between the main and additional parts of the device;
• Compared to the voltage indicators presented above, it is quite cumbersome;
• cannot determine where the phase is and where the zero is;
• The ambient temperature for stable operation of the device is limited from -10 to +50 degrees Celsius.

Conclusion: This indicator is good in professional electrical work. For household needs, in addition to it, it is better to purchase an indicator screwdriver.

In any technology, LEDs are used to display operating modes. The reasons are obvious - low cost, ultra-low power consumption, high reliability. Since the indicator circuits are very simple, there is no need to purchase factory-made products.

From the abundance of circuits for making a voltage indicator on LEDs with your own hands, you can choose the most best option. The indicator can be assembled in a couple of minutes from the most common radioelements.

All such circuits are divided into voltage indicators and current indicators according to their intended purpose.

Working with a 220V network

Let's consider the simplest option - phase checking.

This circuit is a current indicator light found on some screwdrivers. Such a device does not even require external power supply, since the potential difference between the phase wire and the air or hand is sufficient for the diode to glow.

To display mains voltage, for example, checking the presence of current in the socket connector, the circuit is even simpler.

The simplest current indicator on 220V LEDs is assembled using capacitance to limit the current of the LED and a diode to protect against reverse half-wave.

DC Voltage Check

Often there is a need to ring the low-voltage circuit household appliances, or check the integrity of the connection, for example, the wire from the headphones.

As a current limiter, you can use a low-power incandescent lamp or a 50-100 Ohm resistor. Depending on the polarity of the connection, the corresponding diode lights up. This option is suitable for circuits up to 12V. For higher voltages, you will need to increase the limiting resistor.

Indicator for microcircuits (logic probe)

If there is a need to check the performance of a microcircuit, a simple probe with three stable states will help with this. If there is no signal (open circuit), the diodes do not light up. If there is a logical zero on the contact, a voltage of about 0.5 V appears, which opens transistor T1; if there is a logical one (about 2.4 V), transistor T2 opens.

This selectivity is achieved due to the different parameters of the transistors used. For KT315B the opening voltage is 0.4-0.5V, for KT203B it is 1V. If necessary, you can replace the transistors with others with similar parameters.