In everyday work, electricians often need to take voltage measurements and test circuits and wires for integrity. Sometimes you just need to find out whether a given electrical installation is energized, whether the socket is de-energized, for example, before changing it, and similar cases. A universal option that is suitable for making all these measurements is to use a digital multimeter, or at least an ordinary pointer Soviet ABO meter, often called “ Tseshka”.

This name came into our speech from the naming of the device Ts-20 and more recent versions of Soviet production. Yes, modern digital multimeter a very good thing, and is suitable for most measurements carried out by electricians, with the exception of specialized ones, but often we do not need all the functionality of a multimeter. Electricians often carry with them, which is a simple continuity tester, powered by batteries, and indicating the continuity of the circuit on an LED or light bulb.

The photo above shows a two-pole voltage indicator. And to control the presence of a phase, use an indicator with a screwdriver. Two-pole indicators are also used, with an indication, as in the case of a screwdriver indicator, on a neon lamp. But we now live in the 21st century, and electricians used these methods in the 70s and 80s of the last century. Now all this is long outdated. Those who don’t want to bother with manufacturing can buy a device in the store that allows you to ring circuits, and it can also show, by lighting a certain LED, the approximate voltage value in the circuit being tested. Sometimes there is a built-in function for detecting diode polarity.

But such a device is not cheap, I recently saw it in a radio store for a price of around 300, and with extended functionality - 400 rubles. Yes, the device is good, there are no words, multifunctional, but among electricians there are often creative people who have knowledge of electronics that goes at least minimally beyond the scope of basic course college or technical school. This article was written for such people, because these people who have assembled at least one or a couple of devices with their own hands, they can usually estimate the difference in the cost of radio components and the finished device. I can tell you from my own experience, if of course it is possible to choose a case for the device, the difference in cost can be 3, 5, or more times lower. Yes, you will have to spend the evening assembling it, learning something new for yourself, something you didn’t know before, but this knowledge is worth the time spent. For knowledgeable people, radio amateurs, it has long been known that electronics in a particular case is nothing more than assembling a kind of LEGO set, albeit with its own rules, which will take some time to master. But you will have the opportunity to independently assemble, and if necessary, repair any electronic device, initial, and with the acquisition of experience and average complexity. Such a transition, from an electrician to a radio amateur, is facilitated by the fact that the electrician already has in his head the base necessary for study, or at least part of it.

Schematic diagrams

Let's move from words to action, I will give several probe circuits that can be useful in the work of electricians, and will be useful to ordinary people when carrying out wiring, and others similar cases. Let's go from simple to complex. Below is a diagram of the a simple probe- arches on one transistor:

This probe allows you to test wires for continuity, circuits for the presence or absence of a short circuit, and, if necessary, also tracks on a printed circuit board. The resistance range of the dialed circuit is wide, ranging from zero to 500 ohms or more. This is the difference between this probe and the arcade, which contains only a light bulb with a battery, or an LED connected with a battery, which does not work with resistances from 50 Ohms. The circuit is very simple and can be assembled even by surface mounting, without bothering with etching and assembly on a printed circuit board. Although, if foil PCB is available and experience allows, it is better to assemble a probe on the board. Practice shows that devices assembled by surface mounting may stop working after the first fall, while this will not affect a device assembled on a printed circuit board, unless, of course, the soldering was done well. Below is printed circuit board of this sample:

It can be made either by etching or, due to the simplicity of the design, by separating the tracks on the board from each other with a groove cut with a cutter made from a hacksaw blade. A board made in this way will be no worse in quality than an etched one. Of course, before applying power to the probe, you need to make sure that there is no short circuit between sections of the board, for example, by testing.

Second sample option, which combines testing functions that allow testing circuits up to 150 kiloOhms, and is even suitable for testing resistors, starter coils, transformer windings, chokes and the like. And a voltage indicator, both direct and alternating current. At DC The voltage is shown from 5 volts to 48, possibly more, I have not checked. Alternating current shows 220 and 380 volts easily.
Below is the PCB for this probe:

Indication is carried out by lighting up two LEDs, green when dialing, and green and red when voltage is present. The probe also allows you to determine the polarity of voltage at direct current; the LEDs light up only when the probe probes are connected in accordance with the polarity. One of the advantages of the device is the complete absence of any switches, for example, the limit of the measured voltage, or dialing modes - voltage indication. That is, the device operates in both modes at once. In the following figure you can see a photo of the assembled probe:

I collected 2 such probes, both still work fine. A friend of mine uses one of them.

Third sample option, which can only ring circuits, wires, tracks on a printed circuit board, but cannot be used as a voltage indicator, is an Audio probe, with additional LED indication. Below is its schematic diagram:

I think everyone has used audio dialing on a multimeter, and they know how convenient it is. When making a call, you do not need to look at the scale or display of the device, or at the LEDs, as was done in previous probes. If our circuit rings, then a beeping sound is heard with a frequency of approximately 1000 Hertz and the LED lights up. Moreover, this device, like the previous ones, allows you to ring circuits, coils, transformers and resistors with a resistance of up to 600 Ohms, which is sufficient in most cases.

The picture above shows the audio probe circuit board. The audio dialing of a multimeter, as is known, only works with resistances up to a maximum of ten ohms or a little more; this device allows dialing in a much larger range of resistances. Below you can see a photo of the sound probe:

For connection to the circuit being measured, this probe has 2 sockets compatible with multimeter probes. I assembled all three probes described above myself, and I guarantee that the circuits are 100% working, do not need adjustment and start working immediately after assembly. It is not possible to show a photo of the first version of the sampler, as this sampler was recently given to a friend. Printed circuit boards of all these probes for the sprint-layout program can be downloaded in the archive at the end of the article. Also, in Radio magazine and on resources on the Internet, you can find many other probe circuits, sometimes supplied directly with printed circuit boards. Here are just a few of them:

The device does not require a power source and operates when dialing from the charge of an electrolytic capacitor. To do this, the probes of the device need to be plugged into a socket for a short time. When ringing, LED 5 lights up, voltage indication LED4 is 36 V, LED3 is 110 V, LED2 is 220 V, LED1 is 380 V, and LED6 is a polarity indication. It looks like this device is similar in functionality to the installer’s sample shown at the beginning of the article in the photo.

The figure above shows a diagram of a probe - a phase indicator, which allows you to find the phase, ring circuits up to 500 kiloOhms, and determine up to 400 Volts, as well as voltage polarity. On my own behalf, I will say that it is possible to use such a probe less convenient than the one described above and which has 2 LEDs for indication. Because there is no clear certainty about what this probe shows in this moment, the presence of voltage or the fact that the circuit is ringing. Of its advantages, I can only mention that it can determine, as already written above, a phase wire.

And at the end of the review, I will give a photo and diagram of a simple probe, in a marker body, which I assembled a long time ago, and which any schoolchild or housewife can assemble if the need arises :) This probe will be useful on the farm, if you don’t have a multimeter, for testing wires, determining the functionality of fuses and the like.

The figure above shows a diagram of this probe that I drew, so that anyone, even someone who does not know a school physics course, could assemble it. The LED for this circuit needs to be taken from the Soviet Union, AL307, which glows at a voltage of 1.5 Volts. I think, after reading this review, every electrician will be able to choose a sampler according to his taste and degree of complexity. Author of the article AKV.

Discuss the article REVIEW OF ELECTRICAL TESTS

In this article I want to show you how to make a simple tester for NPN transistors structures, with your own hands. If you are assembling any circuit and want to use used transistors in it, then you can easily check its performance with this tester! This diagram was found on an American website, translated and published! 2 schemes are offered.

I'll tell you in a nutshell, for those who don't know how a transistor works. In fact, in simple terms, a transistor is nothing more than a micro switch, only it is controlled by current. The transistor has 3 terminals, emitter-base-collector. In order for the transistor to work, a small current is supplied to the base, the transistor opens and can pass more current through the emitter and collector. Using the proposed tester, you can check whether the transistor has any defects.

Transistor tester circuit 1

Parts List

• Resistor 330 Ohm - 1 pc.
• Resistor 22 kOhm - 1 pc.
• LED - 1 pc.
• Krona 9 Volt - 1 pc.
• Circuit board
• Crown stamps

Solder all the parts onto a piece of circuit board. The contacts for connecting the transistor under test can be made from thick wire, or best of all, bite off the legs from a powerful resistor, divide them into 3 equal parts and solder them to the board.

Below is a finished tester with a connected transistor. As you can see, the LED is on, which means the transistor is open, current is flowing, which means it is working. If the LED does not light up, it will no longer be possible to use it.

I bring to your attention a development that will make life easier for people involved in the installation of multi-core cables. This topic is not new, but I wanted to do something of my own. And the idea for the device was suggested by my work colleague. He often does installation work and he really needs such a device. The cable tester consists of a transmitter that has 22 pins and generates 22 digital values ​​from 1 to 22, and a receiver that recognizes these values ​​and displays them on the indicator. Using the device is very simple: on one side of the cable being called, we connect the digital terminals of the transmitter and the common one to the required cores, which can be connected either to the cable screen or to a colored core so that it would be easier to find it at the other end of the cable. On the other hand, connect the common receiver, and with the input we touch each cable core in turn and look at the indicator. When the receiver recognizes the supplied signal from the transmitter, a digital value will be displayed on the indicator.

Here is the transmitter diagram

Finished PCB

And a photo of the device in the case.

Here is the receiver circuit

Such a chaotic connection of the 7-segment indicator is caused by the fact that the printed circuit board was drawn first and it was convenient to arrange the conductors from the indicator to the microcircuits.

Receiver PCB

When the receiver is turned on, dashes are displayed on the indicator until a signal is received from the transmitter

Here is a photo of the device in action

The receiver recognized the first output of the transmitter

Another photo of the device in operation

The receiver recognized pin 16 of the transmitter.

Unfortunately with the receiver housing question c was not resolved and the device was tested as shown in the photo. Regarding the receiver display, I’ll say a few words: if the value supplied to the receiver is less than 10, then the first digit indicating the tens goes out. This is done in order to save some battery. During field tests, the device showed the following results: the length of the tested cable was 850 meters (it was not possible to find a longer one), the maximum line resistance was 3 kOhm.

As for the MK firmware. I flashed the program: the transmitter controller is flashed to the internal oscillator at 8 MHz, the rest is by default. The receiver is wired for 9.6 MHz as well as an internal oscillator, the rest is default.

When installed correctly, the devices begin to work immediately.

Due to numerous requests, I posted a video of the new version of the device in operation.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
IC1	MK AVR 8-bit	ATmega8	1			To notepad
	Linear regulator	LM78M05	1			To notepad
	Composite transistor	ULN2003	4			To notepad
	Diode	M7	1			To notepad
HL1	Light-emitting diode		1			To notepad
	Capacitor	0.1 µF	1			To notepad
	Electrolytic capacitor	0.22 µF	1			To notepad
	Resistor	240 Ohm	3			To notepad
	Resistor	10 kOhm	1			To notepad
General, 1-22	Terminal clamp		23			To notepad
SA1	Switch		1			To notepad
B1	Battery	9 V	1			To notepad
	Receiver circuit.
IC1	MK AVR 8-bit	ATtiny13	1			To notepad
DD1, DD2	Shift register	SN74HC595	2			To notepad
VR1	Linear regulator	LM7805	1			To notepad
OC1	Optocoupler	PC817	1			To notepad
VD1	Zener diode	5.1 V	1			To notepad
D1	Rectifier diode	1N4001	1			To notepad
R1, R4-R17	Resistor	240 Ohm	15			To notepad
R2	Resistor	4.7 kOhm	1

The problem of testing freshly laid local network always relevant. Once upon a time I came across a piece of hardware called “Rapport II”, which, generally speaking, is a tester for CCTV systems, but twisted pair He also knows how to call. That piece of hardware died a long time ago, but the impression remains: when testing a twisted pair cable, it showed not just polarity reversal and uncoupling, but an exact crimping pattern! For example, for a crossover it looked like 1 → 3, 2 → 6, 3 → 1, and so on.
But to pay about 800 non-Russian rubles for a device in which I will actually use only one function? Excuse me! How does it work, maybe it’s easier to do it yourself? Google in hand, and... complete disappointment. The search output consists of 80% LED flashing lights on shift register/ AVR / PIC / your own version, and 20% from the thoughtful discussions of forum gurus on the topic “buy %name_of_cool_hardware_for_100499.99_evergreen% and don’t worry.” Therefore, I want to offer the habra community my solution to this problem in DIY style. If anyone is interested, please see the cut below (be careful, there are a lot of photos!).

Introductory

Determining the exact cable crimping pattern is mandatory.
All information is displayed from the tester side. No blinking LEDs on the response part. Suppose that the response part is in the hands of a monkey, and not even a circus one, and only thanks to the latest technologies The monkey was trained to use a hammer drill and cross-connect cables in sockets. Or, to put it a little more scientifically: the response part is completely passive.

Hardware

Operating principle: the response part is a set of resistances of various values. Let's measure them. Knowing their ratings and the wiring of the mating part, we can find out exactly how the cable is crossed. Below is a diagram of the device (all illustrations are clickable). Specific resistance values ​​were chosen based on availability in the store rather than deliberately, although a piece of the Fibonacci series was obtained.

The tester's work is divided into several stages, which are repeated cyclically.

Stage 1: Initial checks

• Let's check if any active equipment. We transfer all control lines (port C, let me remind you) to the Hi-Z state, measure the voltage on all lines. They should be near zero. Otherwise, we understand that anything is connected on the other side of the wire, but not our counterpart, and there is no point in continuing further. But it makes sense to inform the user that “there is voltage on the line!”
• Let's check the signal level on PB2. If there is 0, then the battery is discharged. We will report the problem to the user, if everything is OK, move on.

Stage 2. Checking the integrity of the lines and the presence of short circuits

For each of the 8 lines we do the following. We supply +5V to it from port C, keeping all other lines of the port in a high-impedance state, and measure the voltage on the remaining lines. If all lines have near-zero values, the line under study is broken. If +5V also appears on one of the lines, this is a short circuit. Normally, we will see some intermediate values.

Stage 3. Determining the cross-connection scheme

Now we get to the most interesting part. Having weeded out all obviously faulty lines (broken and shorted wires), we proceed to measuring the resistance of the remaining lines (let their number be N, 0<= N <= 8). Введем обозначения:
R xy - resistance between lines x and y.
R x is the value of the resistance connected to line x.
It is clear that R xy = R x + R y

By measuring the resistance between the lines, we obtain a system of linear equations. By comparing the obtained values ​​of R 1 ... R N with the reference ones, we will find out the cross-connection scheme.

Resistance is easy to calculate. Let's apply a high level to line X, a low level to line Y, and leave the other lines of port C in Hi-Z. In the circuit (see Fig. 3), the voltage drop across the known resistance formed by the parallel connection of R1.Y and R2.Y according to the circuit is U 1, and at the unknown R xy it drops (U 2 - U 1). This means R xy = (R 1 || R 2) * (U 2 - U 1) / U 1.

Rice. 3. Resistance measurement principle

If N< 3 - мы бессильны. Мы можем произвести всего одно измерение сопротивления между ними, в то время, как имеем 2 неизвестных - сопротивление, подключенное к каждой из них. Система, в которой число уравнений меньше числа неизвестных, имеет бесконечное множество решений. Придется показать пользователю знаки вопроса на этих линиях - они вроде бы исправны, но выяснить схему кроссировки возможным не представляется.

When N = 3 we have only one possible option. Having measured all available resistances R 12, R 13, R 23, we get the system:
R 1 + R 2 = R 12
R 1 + R 3 = R 13
R 2 + R 3 = R 23
It is easy to show that:
R 1 = 1/2 * (R 12 + R 13 - R 23)
R 2 = R 12 - R 1
R 3 = R 13 - R 1.

With b O At higher values ​​of N, we can compose a system of equations in many ways, taking measurements of various resistances R xy. At first glance, there is no difference in how to choose which resistances to measure. However, the devil is in the details. Using the example of N = 8, I will explain what I mean. In the first implementation of the algorithm, I made measurements like this:
R 1 + R 2 = R 12
R 1 + R 3 = R 13
…
R 1 + R 8 = R 18
R 2 + R 3 = R 23
Adding the first two equations and subtracting the last, we get the same thing: 2R 1 = R 12 + R 13 - R 23, and we find all other resistances from equations 1 - 7, where R 1 is already known.

The problem lies in the fact that with some types of cross-connection, the value of R 1 turned out to be large (15 kOhm and above), and the error in measuring resistance increases with its increase. As a result, it turned out that small resistances relative to R 1 with a nominal value of 1-2 kOhm were measured with an error of 70-80%! Obviously, to ensure good accuracy, we should compose the system so that in place of R 1 there is another unknown, the smallest of all. To do this, we will have to perform all possible measurements (it’s good that there are not many of them, in the worst case 28). In fact, we have obtained an 8 x 8 matrix, symmetrical about the main diagonal (clearly, R xy = R yx). Let us choose the minimal one from all the results, let it be R ij = R i + R j . In line i we find R ik, such that R ik > R ij, but less than other elements of the line. We get:
R i + R j = R ij
R i + R k = R ik
Rj + Rk = Rjk
We solve and find the smallest among R i, R j, R k (let’s assume it turns out to be R i). the remaining unknowns R x are found from R x = R ix - R i .

Stage 4. Determining the break point, if any

Smart and expensive hardware measures the distance to the break point using TDR. Difficult, expensive, cool. Our capabilities are much more modest, and it’s not so often that we need to know the position of a cliff down to centimeters - usually an understanding in the style of “right next to me”, “at the other end”, “in the middle where the wall was recently chiseled” is more than enough. So - measuring the cable capacitance.

We convert all lines of port C, except the one connected in the core where there is a break, to Hi-Z. We apply +5V to the core, charging it. Let's measure the voltage on it, this will be our initial U 0 . Convert all lines to Hi-Z. The cable discharge begins through resistor R2.X with a resistance of 1 MOhm. After waiting 1 ms, we measure the voltage on this line U.

We must not forget that the circuits on the board, connector, etc. also have their own capacity, so the device needs to be calibrated on a couple of pieces of cable of different lengths. I got 1710 pF at zero length, and the cable capacitance was 35 pF / m. Practice has shown that even if it lies, it’s not much, by 10 percent. A situation like “where did you miss the contact, in the closet on the patch panel or in the socket? solved instantly.