Chip voltage probe. Improved Probe

The simplest work related to electricity is difficult to perform without measuring tools.
It is not at all necessary to measure the parameters of the electrical circuit with a tester; in many cases it is more convenient to get by with a universal probe that infects the presence of these parameters by means of light signals. This is quite enough for convenient and safe work with electrical circuits.
The considered probe-indicator circuit does not contain batteries. Instead of the energy normally used in batteries, probes use the energy of a charged capacitor.

Functionality.
The probe allows you to control the presence of alternating and direct voltage in the range from 24 to 220 V, carry out continuity of an electrical circuit with a resistance of up to 60 kOhm, and determine the polarity in DC circuits.
When the probes XP1 and XP2 are connected to a DC source in accordance with the polarity of the input, the green LED HL1 lights up, indicating not only the presence of a constant voltage in the controlled circuit, but also the presence of a plus at the touch point of the XP1 probe.
Reversing the polarity on the probes causes the red HL2 LED to light up, which, in addition to the presence of voltage, indicates contact with the plus of the HP2 probe.
When the AC voltage is being monitored, both LEDs light up simultaneously.
The continuity of the circuit during continuity is indicated by the red LED HL2 lighting up.
This is the information you can get with just two LEDs built into this simple indicator probe.

Probe design.

Radio components. To implement the device, you must purchase or find in your stock the following parts:
Resistors R1-220 kOhm and R2-20 kOhm, power 2W, R3-6.8 kOhm;
LEDs HL1 - AL 307G, HL2 - AL 307B;
Diodes KD2 - VD5 - KD103 (possible replacement for KD 102);
Zener diode VD1 - KS222Zh (possible replacement for KS220Zh, KS522A);
Capacitor C1 - K50-6 1000x25.

Frame. Particular attention should be paid to the choice of case - the convenience of working with the probe depends on its configuration and dimensions. Let's consider two cases. In the first option, the relay cover is used, in the second, the case of an unknown gadget.

Holes are made in the cases for the output of the wire with the XP2 probe, LEDs are installed (only for the first option) and the XP1 probes are attached.
Pay. The package dimensions determine the board geometry. Mounting can be hinged, but it is not difficult to do it on a printed circuit board. All radio components (except LEDs in the first version) are mounted on a board that is mounted inside the case.

After installing the board in the case and soldering the conductors to the XP1 and XP2 probes, the probes-indicators are ready for operation. The device does not need to be adjusted.
The charge time of the probe capacitor at a voltage in the network within 220-24V is 3-25 seconds. The capacitor discharge time in case of a short circuit of the probe probes is at least 2 minutes.

Checking the voltage in the circuit is a procedure necessary when performing various kinds of work related to electricity. Some amateur electricians, and sometimes professionals, use a home-made “control” for this - a cartridge with a light bulb to which wires are connected. Although this method is prohibited by the "Rules for the safe operation of consumer electrical installations", it is quite effective when used correctly. But still, for these purposes, it is better to use LED determinants - probes. You can buy them in the store, or you can make your own. In this article, we will tell you why these devices are needed, on what principle they work, and how to make a voltage indicator on LEDs with your own hands.

What is a logic probe for?

This device is successfully used when it is necessary to perform a preliminary check of the operability of elements of a simple electrical circuit, as well as for primary diagnostics of simple devices - that is, in cases where high measurement accuracy is not required. With a logic probe, you can:

Determine the presence in the electrical circuit of a voltage of 12 - 400 V.
Determine the poles in the DC circuit.

Check the condition of transistors, diodes and other electrical components.
Determine the phase conductor in the AC electrical circuit.
Ring the electrical circuit to check its integrity.

The most simple and reliable devices with which the listed manipulations are performed are an indicator screwdriver and a sonic screwdriver.

Electrician's probe: principle of operation and manufacture

A simple determinant on two LEDs and with a neon light bulb, which received the name “arkashka” among electricians, despite a simple device, allows you to effectively determine the presence of a phase, resistance in an electrical circuit, and also detect a short circuit (short circuit) in the circuit. Universal electrician tester is mainly used for:

Diagnostics for broken coils and relays.
Ringing of motors and throttles.
Checking rectifier diodes.
Pin definitions on transformers with multiple windings.

This is not a complete list of tasks that are solved with the help of a probe. But the above is enough to understand how useful this device is in the work of an electrician.

The power source for this device is a conventional battery with a voltage rating of 9 V. When the tester probes are closed, the amount of current consumed does not exceed 110 mA. If the probes are open, then the device does not consume electricity, so it does not need either a diagnostic mode switch or a power switch.

The probe is able to fully perform its functions until the voltage on the power supply drops below 4 V. After that, it can be used as a voltage indicator in circuits.

During the continuity of electrical circuits, the resistance of which is 0 - 150 Ohm, two light-emitting diodes light up - yellow and red. If the resistance indicator is 151 Ohm - 50 kOhm, then only the yellow diode is lit. When a mains voltage of 220 V to 380 V is applied to the probes of the device, a neon lamp starts to glow, at the same time, a slight flicker of the LED elements is observed.

A diagram of this voltage indicator is available on the Internet, as well as in specialized literature. When making such a probe with your own hands, its elements are installed inside the case, which is made of insulating material.

Often, for these purposes, a case from the memory of any mobile phone or tablet computer is used. From the front of the case, a probe pin should be removed, from the end - a high-quality insulated cable, the end of which is equipped with a probe or a crocodile clip.

Assembling the simplest voltage probe with an LED indicator is in the following video:

How to make a do-it-yourself electrician's evuk tester?

Some thrifty fans in the "arsenal" can find a lot of useful things, including an earpiece (capsule) for the TK-67-NT phone.

Another similar device is also suitable, equipped with a metal membrane, inside of which there is a pair of series-connected coils.

On the basis of such a part, a simple sound probe can be assembled.

First of all, you need to disassemble the telephone capsule and disconnect the coils from each other. This is necessary in order to release their conclusions. The elements are placed in the earpiece under the sound membrane, near the coils. After assembling the electrical circuit, we will get a completely working determinant with sound indication, which can be used, for example, in order to check the tracks of printed circuits for mutual bridging.

The base of such a probe is an electric generator with an inductive opposite relationship, the main parts of which are a telephone and a low power transistor (preferably germanium). If you do not have such a transistor, then you can use another one with N-P-N conductivity, but in this case, the polarity of the power supply should be reversed. If the generator cannot be turned on, the conclusions of one (any) coil must be interchanged.

You can increase the volume of the sound by selecting the frequency of the generator so that it is as close as possible to the resonant frequency of the earphone. To do this, the membrane and the core must be placed at an appropriate distance, changing the interval between them until the desired result is obtained. Now you know how to make a voltage indicator based on a telephone earpiece.

Visually, the manufacture and use of the simplest voltage probe on the video:

Conclusion

In this article, we talked about how you can assemble a voltage indicator on LEDs with your own hands, and also considered the issue of making a simple diagnostic tool based on an audio earpiece.

As you can see, it is not difficult to assemble an LED indicator on your own, as well as a sound determinant - for this it is enough to have a soldering iron and the necessary parts on hand, as well as to have minimal electrical knowledge. If you don’t really like to assemble electrical devices on your own, then when choosing a device for simple diagnostics, you should stop at a regular indicator screwdriver, which is sold in stores.

This voltage indicator, also known as an electrician's probe, will allow you to determine the phase, the location of a short circuit or an open circuit in the AC network, it will make it possible to ring the motor windings and check the rectifier diodes. For ease of manufacture and ease of use, the electrician's probe does not have an operating mode switch and a power switch. But it has two LEDs of different colors, as well as a regular neon lamp

If the probe probes are closed, then the current consumption will be about 100 mA, if the probes are open, the current consumption tends to zero. It is easiest to power our home-made device from the Krona battery, but if its volts drop even to 4 V, the probe will continue to work.

During the continuity of the resistance in the range from 0 to 150 ohms, the green LED lights up, if the resistance is in the range from 150 ohms to 50 kOhm, the yellow LED lights up. During the measurement of AC voltage 220 - 380 V, the neon lamp lights up, and the LEDs will flicker a little.

Voltage indicator transistor circuit

The probe circuit is assembled on three transistors. At the initial moment, all transistors will be locked. If we close the probe probes, then the positive component of the voltage passes through the diode VD1 and the resistor R5 to the gate of the unipolar transistor, which opens under the influence of the field and contributes to the opening of the bipolar transistor V3.

During the supply of mains voltage to the probes, the neon light HL1 will light up, in addition, the rectified mains voltage from the diode VD1 is supplied to the zener diode VD3, and as soon as it reaches 12 volts, the transistor V2 will open, which will close the field effect transistor V1. The LEDs will flicker slightly.

Transistors V2, V3 can be taken 13003A from a conventional energy-saving lamp. Zener diode D814D, KS515A or any other with a stabilization voltage of 12-18 V. The neon lamp can be taken from the indicator screwdriver. Any rectifier diode with a current of at least 0.3 A and a reverse voltage of 600 volts is suitable, you can choose it from.

The probe will start working immediately if it was assembled correctly and does not need to be configured. The first range of 0-150 ohms, if necessary, can be changed by selecting the resistor R2.

This probe has two types of signaling - sound and light and two thresholds for turning on the sound signal - with the resistance of the measured circuit up to 50 Ohm and up to 1 kOhm. Therefore, it can be used to check the health of p-n junctions of transistors and diodes.

Voltage indicator on logic chip

If the probe probes are open or the resistance of the controlled circuit is more than the limit set by the switch, the transistor VT1 is locked and the DD1.2 element has a logical zero, so the audio frequency generator does not generate pulses. When we close the probes at the “50 Ohm” switch position, a current of about 3.6 mA will flow through the diodes VD1-VD3 and resistors R1-R3 and the “U” drop across the resistor R1 will be quite enough to open the transistor. The HL1 LED will light up, and the AF generator will start generating pulses with a frequency of about 1.2 kHz and an audible signal will sound. Resistor R10 is designed to reduce the volume of the signal, and resistance R8 limits the current flowing through the LED.

Series-connected resistors R1, R4, R7, or rather their total resistance sets the sensitivity of the probe. The higher it is, the higher the resistance of the controlled circuit will sound an audible signal. If the contacts of the switch SA1 are open, the probe is in the mode of measuring the continuity of circuits with a resistance of up to 1000 ohms. Diodes VD1-VD4 and resistor R3 will protect the electrician's probe from damage if the probes are erroneously connected to an under-pressure circuit or to a charged capacitor. But the possibilities of this protection are not perfect, remember this.

The probe setting consists in the selection of resistors R1, R4, R7. In mode 50 ohm resistor R1 sets the threshold for turning on the signal when the resistance of the controlled circuit is 50 ohms or less. In the 1 kΩ mode, resistors R4 (coarse) and R7 (fine) set the threshold to 1 kΩ. The voltage on the probe probes has polarity, so it is desirable to highlight them, for example, with colored heat-shrink sleeves.

On two LEDs of different colors, you can make a simple voltage probe indicator from 4.5 to 220 V. It can also determine the polarity of the power source. When checking the presence of variable "U", both diodes are lit, and if "U" is constant, only one of them is lit, depending on the polarity of the voltage indicator connection. The scheme was proposed by the Czechoslovak amateur radio magazine Amaterske Radio.

Ratings from 110 to 220 volts of alternating current should be measured for a short time so that the current-limiting resistance R1 does not overheat.

Czech zener diodes 1NZ70 can be replaced with domestic counterparts D815A, diodes V1 and V5 - with any low-power silicon, for example, one of the most common D226.

Voltage indicator on one LED

The performance of the circuit is guaranteed in the range from 3 to 30 volts. At the initial moment of time, when a controlled level appears at the input terminals, current flows through the resistances R1-R4, the LED and the resistor R5. It causes a voltage drop across the current sensor R5. As soon as the magnitude of this drop increases for the VT1 bipolar transistor to open enough, the latter will open, and part of the current will pass through it. This current will create an even greater drop across the resistances R1-R4, maintaining a constant voltage on the plus side of the LED, regardless of the input value. At 30 volts, the current flowing through the resistances R1 ... R4 can reach a nominal value of one hundred milliamps.

Given the magnitude of the current and the value of the drop across these resistances, I had to use four resistors, not one. In the role of transistor VT1, you can take KT603A, which has a constant collector current of about 300mA and a power dissipation of 0.5 W. You can also use KT815, but with a small heat sink.

DC and AC voltage indicator on LEDs

Using this probe, you can check for the presence of voltage, determine its nature (constant or variable), and also ring the circuit for serviceability. The HL2 LED indicates the presence at the input (XP1 and XP2 plugs) of a constant voltage of a certain polarity. If a plus is supplied to the XP1 plug, and a minus to the XP2, then current flows through the current-limiting resistance R2, the VD2 diode, the VD3 zener diode and the LED itself, so HL2 will burn. Moreover, its brightness depends on the input voltage level. With reverse polarity, it will not burn.

The HL1 LED indicates the presence of an AC voltage probe at the input. It is connected through a current-limiting capacitor C1 () and a resistor R3, a diode VD1 - which protects the LED from the negative half-wave of the alternating voltage. Simultaneously with the HL1 LED, HL2 will also light up. Resistance R1 is designed to discharge capacitance C1. The minimum voltage level at which the LED starts to burn is 8 V.

High-capacity C2 was used as a power source for "ringing" the connecting wires. Before testing, it must be charged by connecting to a 220 volt network for fifteen minutes. The ionistor is charged through the components R2, VD2, HL2, the voltage on it is limited by the zener diode VD3. After that, the probe input is connected to the circuit under test and SB1 is pressed. If the wire is good, through it, the button contacts, the LED HL3, R4, R5 and the fusible insert FU1 current follows and HL3 starts to burn. The energy reserve in the ionistor is enough for 20 minutes of work.

Often in amateur radio practice, when using various home-made power supplies and chargers, it becomes necessary to determine the polarity at their output. Of course, this is easy to do with a multimeter, but if you have a device for determining the polarity at hand, then you can determine “plus” or “minus” much faster, besides, the measuring device in the first version does not even require its own power source and is ready to use at any time. work.

When testing, setting up and repairing various electronic equipment, it often becomes necessary to quickly check for the presence of voltage and determine its polarity at different points of the device, wires, power connectors, etc. For these purposes, especially during work in the "field" conditions, it is convenient to use simple small-sized probes-indicators.
On fig. 1 shows a diagram of a simple voltage and polarity probe on a two-color HL1 LED. Indicator input voltage -
3.5 ... 18 V, the current consumption is approximately 1 to 15 mA. In accordance with the flowing current, the brightness of the LED also changes.
Resistor R1 limits the current through the LED, and the diodes VD1 and VD2 are turned on so that, depending on the polarity of the controlled voltage, one of the LED crystals shines. When a positive polarity voltage is applied to the input, the current flows through the current-limiting resistor R1, the red glow crystal and the VD2 diode, and therefore the glow of the HL1 LED will be red. When the polarity is reversed, it will turn green. If the input voltage is AC, the glow color is yellow.

Circuits. Low voltage probes. Voltage indicators

In some cases, it is necessary not only to check the voltage and polarity of various power sources, such as batteries or galvanic cells, but also to assess their condition and load capacity. To do this, it is convenient to use a probe, which includes a load that consumes a certain current. Incandescent lamps can be used as a load. The scheme of such a probe is shown in Fig. 2. With its help, the polarity of the controlled voltage is determined, for this, the EL1 lamp should be painted with heat-resistant varnish or covered with a red light filter, and EL2 - green. The operating voltage of the probe and the current consumed by it are determined by the applied incandescent lamps. For a small-sized probe, miniature lamps of the Media series are suitable.
To check the various nodes of the HF radio transmitting equipment in which high-frequency voltage is present, you can use a probe, the circuit of which is shown in Fig. 3. It operates in the frequency range of 1 ... 30 MHz and indicates voltage from 1.5 to 20 V. The input (XP1) is connected to the controlled circuit, and the XP2 probe is connected to the common wire. Capacitor C1 is a ballast and limits the input high-frequency current, diodes VD1, VD2 rectify the alternating voltage, resistor R1 additionally limits the current through the HL1 LED.
By selecting capacitor C1, you can change the sensitivity of the probe. An increase in the capacitance of this capacitor, along with an increase in sensitivity, leads to an increase in the shunting effect on the controlled circuits due to a decrease in the input resistance of the device. When working with a probe, it is recommended to first connect only the XP1 input to the circuit, without connecting the XP2 probe to the common wire. If the LED is not lit, the XP2 probe is also connected.
The basis of all probes can be a transparent case of a fountain pen with an inner diameter of at least 7 mm. Most of the elements are placed in it, connected by pieces of a mounting wire, and the soldering points are insulated with PVC tubes. As an XP1 probe, you can use a pin from a connector or a sewing needle. To connect the indicator to the common wire of the device, a flexible stranded wire 10 ... 20 cm long is used, at the end of which you can install a crocodile clip.
The probes use MLT, S2-23 resistors, a capacitor - KM-5, KT, K10-17, KD103A diodes are replaceable by any low-power rectifiers, KD521A - by KD510A, KD522B diodes. LEDs - in a plastic case with a diameter of 3 ... 5 mm with increased brightness.
Download: Low voltage probes. Voltage indicators
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Working with existing electrical installations and cable and wire products is associated with the risk of electrical injury. The reason for this is banal - the directed movement of charged particles along a conductor cannot be seen with the naked eye. Therefore, during installation, maintenance and repair of electrical equipment, a tester must be used to check the voltage.

Able to at least simply show the presence of potential, even without measuring its effective value.

A vital necessity

A voltage tester is a portable electrical device designed to indicate the presence of potential in conductive areas. In electrical networks, not all wires are dangerous when touched. The current beats those on which there is a phase, but the neutral or ground wire is safe. True, there are reservations.

To understand why a voltage tester may be needed at home, it is easiest to give a number of examples. Let's imagine that there was a need for a grinder (grinder), which a neighbor provided for a while. Still used models, the body of which is made of metal. How to check that the internal circuits are intact, and there is no voltage on the shell? Working with such a tool without first checking it is a very risky undertaking. Or, for example, you need to change a burned-out light bulb in a lamp, the glass bulb of which has fallen, and only the base remains in the cartridge. Believe the electricians who did the wiring that the switch really breaks the phase wire, and not the zero one, and boldly unscrew the base? Doubtful! There are many such examples. With your own voltage tester, you can always quickly check the electrical installation area. In addition, more complex models allow measurement of the effective value.

Basic features

To check the presence of a potential (phase), there is no need to spend money on buying an expensive device.

The simplest voltage tester is an indicator screwdriver. Inside its transparent case there is a small light bulb that lights up when the stinger touches the area under potential.

How to check the voltage with a tester? On the upper side of the dielectric handle there is a special metal "penny". To check the section of the circuit, it is necessary to touch the tip of the screwdriver to the conductor being checked, and with your finger to the “penny”. The sting itself cannot be touched. If the phase is present, then the light inside the screwdriver will light up. The second name of such screwdrivers is probes. They are rated for voltages up to 250 V.

It is not recommended to buy the cheapest models, because in the event of a breakdown of the internal resistor or an error in the circuit, you can get More advanced solutions that do not require direct contact with the circuit section. The sting of such a screwdriver just needs to be held over the conductor. Designed for voltages up to 600 V.

In addition, some models are equipped with a display showing the actual value.

There are modifications that do not require touching the penny with your finger. You can easily purchase a voltage tester. The instructions for it must be read. This will not only save the device from damage, but also protect the person himself.

double screwdriver

At the same time, the tool described above is too narrowly specialized. If it is required, for example, to perform the simplest task - phasing, then it turns out to be useless due to the presence of only one pole. In this case, you should pay attention to a more advanced tester - a dual low voltage indicator. Structurally, it can be compared with two screwdrivers connected by a wire. The maximum allowable voltage is 1 kV. Cost - from 100 rubles.

Consider how to measure the voltage with a tester of this class. The sting-electrode of one part must be touched to the checked section of the circuit, and the other - to the "ground". It can be any grounded conductor, since no dangerous potential flows through the device.

If the light inside the case lights up, this will mean that there is voltage in the area. If it is necessary to perform phasing, you need to touch one probe to one phase wire, and the other to the other. If the phase on the wires is of the same name, then there will be no indication. Simpler models show the very fact of the presence of a phase, while more complicated ones contain several LEDs on one of the handles, by the glow of which you can determine the voltage value.

Indicator

The next class of such devices are the most famous models of the Ukrainian manufacturer "Contact". Their cost starts from 400 rubles. Structurally, such testers vaguely resemble twin screwdrivers, but they have more advanced capabilities.

In particular, they can be used to determine the presence of a phase, approximately estimate the voltage level by the glow of the LEDs, and check the conductor for integrity. Inside there is a capacitor, which must be pre-charged by touching the probes to 220/380V for 20-30 s.

How to find a phase wire

Consider how to check the voltage with a tester. One of the probes of the device must be touched to the tested section of the electrical installation, and with a finger of the hand - to the Ph electrode on the body. If the corresponding LED lights up, then this conductor is energized. True, there is one nuance that is very well known to people who know how to work with this type of voltage tester. It lies in the fact that checking the phase through Ph is not always correct, since the readings can be affected by pickups from nearby conductors with current. To clarify: there are two adjacent wires, one of which is energized and the other is de-energized. If you do not know how to work with a voltage tester in detail, then when checking both conductors by touching them and the Ph electrode, it turns out that, according to the indication, they are both phase.

However, it is not. It's just that in a de-energized EMF is induced under the action of It reaches only a few tens of volts, but is determined by the device and is not a failure in its operation. In such cases, if in doubt, you need to do otherwise: touch one probe to the area being checked, and the other to a known grounded point. If there is a phase on the conductor, the LEDs will light up and show an approximate value of 220 V. By the way, having access to a three-phase voltage, you can check the site by touching not only the "ground", but also other phase wires. That is, the actions are similar to performing phasing. If voltage is present in the area, touching the opposite phase will cause the 380 V LEDs to glow.

Features of working with the pointer tester

The specification says that the current flowing through the circuits of the device, when checking the potential of 220 V, is no more than 10 mA. That is, if you touch one of the probes to a section of the electrical installation that is energized, then the ammeter connected to the other probe will show the above current value.

Theoretically, this is a dangerous value (100 mA is lethal), in practice, touching with a hand is possible, however, as long as the internal circuits of the device are working.

Preparing to work with "Contact"

All solutions in which two units are wired together are potentially dangerous. One of their disadvantages is the possibility of damage to the connecting conductive core with visible integrity of the sheath. Therefore, when checking the presence of a phase through Ph, it is recommended to use the probe of the block on which this electrode is located. In this case, the LED will work even if the wire is damaged. Nevertheless, before taking measurements, you need to connect the device to the network and hold it for 20 seconds - during this time, the internal energy source will be charged. After that, you need to connect the probes together. If the wire is intact, then the “test” LED will light up.

Universal Tool

In addition to all these devices, there is another variety - multimeters. Perhaps this is the most advanced voltage tester. How to use it, we will now tell. The cost of the most affordable models starts from 300 rubles. The operating procedure is described in the accompanying instructions, which you need to read. If we talk about checking the voltage, then one wire must be connected to the COM connector, the other to V. Then set the switch to AC 750 mode (alternating current, limit 750 V) and touch the probes to the “ground” and the area being tested.