In that small overview consider the possibility of self-production of such an interesting and useful home appliance in everyday life as a simple tester. Such a simple device is very useful for promptly checking the performance of radio components and for use in everyday life.
Despite the fact that you can buy a tester in stores at a fairly low price, self-assembly of such a small device will be an excellent practice for any novice amateur radio technician.
The assembled device is very convenient and may well be used even by masters of their craft. You can see a photo of a homemade tester in the review below.
Schematic diagram of a simple tester
Such a device includes a minimum number of elements for assembly, which are in use in almost any home or can easily be purchased if necessary at any radio parts store or even in a hardware store.
In essence, this is the only multivibrator that is assembled on a transistor basis. With its help, rectangular-type pulses are generated.
The control circuit of the current is connected to the elements of the multivibrator on a serial basis in opposite and parallel using two color LEDs.
As a result, the circuit to be tested with the device is tested with an AC current, which ensures high accuracy of the test.
How the tester works
An alternating current is removed from the main working component, which is a multivibrator, which is approximately equal in amplitude to that supplied by the power source. Anything above 3.7 V is suitable as a condensing element, for example, 16 or 25 V.
Naturally, with an open circuit, the LEDs do not light up. When the circuit is closed and current flows through the circuit, the LEDs light up. It's simple.
With such a device, you can very quickly and efficiently check any element for performance or a circuit for a break in it. It is very convenient for use at home, especially by a not particularly well trained person. DIY transistor tester - what could be simpler?
Such a device is assembled either using a simple printed circuit board or by means of a hinged mount. Also in the field of application includes the ability to determine the "plus" and "minus" when you do not know where they are in the element under study. For battery use, 2-3 AAA batteries can be used to minimize the size of the device.
The second method of making a compact tester for use in a car. Such a device will have literally 2 main working functions - the ability to read the voltage “on the ground” and the presence of 12 V in the circuit. Moreover, all this will be available literally when one wiring is connected to the machine's network.
What is needed to create such a functional device:
- an ordinary medical syringe for 5 cm3;
- batteries LR-44 in the amount of 4 pieces;
- two small LED elements with a resistor component;
- a small piece of steel wire;
- wiring with a clamp at its end.
Automotive homemade testers circuits
- In the opposite way, we solder both LEDs used in parallel;
- Through the resistor used, one of the ends must be soldered tightly to the steel wire;
- Install batteries one by one directly inside the syringe body. These are chosen because they fit perfectly into a five-cube syringe;
- The probe is isolated from the syringe with a plastic tube, you check the functionality directly in the machine in practice;
- Check if the LEDs on the 12V element light up.
So, the use of the tester made by you yourself is more than conditioned in everyday life. Believe me, such a small device will definitely come in handy, if not in everyday life, then at those moments when you need to check something in your home or car's electrical network.
Making a tester with your own hands can seriously raise the self-esteem of any person who does not believe that he can do anything with his own hands - only desire is important.
Photos of testers with their own hands
Those who like to do everything with their own hands are offered a simple tester based on the M2027-M1 microammeter, which has a measurement range of 0-300 μA, an internal resistance of 3000 Ohm, an accuracy class of 1.0.
Required details
This is a tester that has a magnetoelectric mechanism for measuring current, so it only measures direct current. A moving coil with an arrow is attached to the guy wires. It is used in analog electrical measuring instruments.
Finding radio parts at a flea market or buying radio parts at a store will not be a problem. There you can also purchase other materials and components, as well as attachments to the multimeter. In addition to a microammeter, you will need:
If a person decides to make himself a multimeter with his own hands, it means that he has no other measuring instruments. Based on this, we will continue to act.
Selection of measuring ranges and calculation of resistor values
Let's define the range of measured voltages for the tester. Let's choose the three most common, covering most of the needs of the radio amateur and home electrician. These ranges are 0 to 3 V, 0 to 30 V, and 0 to 300 V.
The maximum current passing through a homemade multimeter is 300 μA. Therefore, the task is reduced to the selection of additional resistance, at which the arrow deflects to full scale, and a voltage corresponding to the limit value of the range will be applied to the serial chain Rd + Rvn.
That is, on the 3 V range, Rtot = Rd + Rvn = U / I = 3 / 0.0003 = 10000 Ohm,
where Rtot is the total resistance, Rd is the additional resistance, and Rvn is the internal resistance of the tester.
Rd = Rtot-Rvn = 10000-3000 = 7000 Ohm or 7kOhm.
On the 30V range, the total resistance should be 30 / 0.0003 = 100000 ohms
Rd = 100000-3000 = 97000 Ohm or 97 kOhm.
For 300 V range, Rtotal = 300 / 0.0003 = 1,000,000 Ohm or 1 mOhm.
Rd = 1000000-3000 = 997000 Ohm or 997 kOhm.
To measure currents, select the ranges from 0 to 300 mA, from 0 to 30 mA and from 0 to 3 mA. In this mode, the shunt resistance Rsh is connected to the microammeter in parallel. therefore
Rtot = Rsh * Rin / (Rsh + Rin).
And the voltage drop across the shunt is equal to the voltage drop across the tester coil and is equal to Upr = Ush = 0.0003 * 3000 = 0.9 V.
Hence, in the range of 0 ... 3 mA
Rtot = U / I = 0.9 / 0.003 = 300 Ohm.
Then
Rsh = Rtot * Rvn / (Rvn-Rtot) = 300 * 3000 / (3000-300) = 333 Ohm.
In the range 0 ... 30 mA Rtot = U / I = 0.9 / 0.030 = 30 Ohm.
Then
Rsh = Rtot * Rvn / (Rvn-Rtot) = 30 * 3000 / (3000-30) = 30.3 Ohm.
Hence, in the range of 0 ... 300 mA Rtotal = U / I = 0.9 / 0.300 = 3 Ohm.
Then
Rsh = Rtot * Rvn / (Rvn-Rtot) = 3 * 3000 / (3000-3) = 3.003 Ohm.
Fitting and installation
To make the tester accurate, you need to adjust the resistor values. This part of the work is the most painstaking. We will prepare a board for installation. To do this, you need to draw it into squares measuring a centimeter by centimeter or slightly less.
Then, with a boot knife or something similar, the copper coating is cut along the lines to the fiberglass base. The result is isolated contact pads. We marked where the elements will be located, it turned out a semblance of a wiring diagram right on the board. In the future, the tester elements will be soldered to them.
In order for a home-made tester to give correct readings with a given error, all its components must have at least the same accuracy characteristics and even better.
The internal resistance of the coil in the magnetoelectric mechanism of the microammeter will be considered equal to the 3000 Ohm declared in the passport. The number of turns in the coil, the diameter of the wire, the electrical conductivity of the metal from which the wire is made are known. This means that the manufacturer's data can be trusted.
But the voltages of 1.5 V batteries may differ slightly from those declared by the manufacturer, and knowledge of the exact voltage value will then be required to measure the resistance of resistors, cables and other loads with a tester.
Determining the exact voltage of the battery
In order to find out the actual voltage of the battery yourself, you will need at least one accurate resistor with a nominal value of 2 or 2.2 kOhm with an error of 0.5%. This resistor value was chosen due to the fact that when a microammeter is connected in series with it, the total resistance of the circuit will be 5000 ohms. Therefore, the current going through the tester will be about 300 μA and the needle will deflect to full scale.
I = U / R = 1.5 / (3000 + 2000) = 0.0003 A.
If the tester shows, for example, 290 μA, then the battery voltage is
U = I * R = 0.00029 (3000 + 2000) = 1.45 V.
Now, knowing the exact voltage on the batteries, having one exact resistance and a microammeter, you can select the required resistance values for shunts and additional resistors.
Collecting the power supply
The power supply for the multimeter is assembled from two series-connected 1.5 V batteries. After that, a microammeter and a 7 kOhm resistor preselected at the nominal value are connected to it in series.
The tester should show a value close to the current limit. If the device goes off scale, then in series to the first resistor it is necessary to connect the second, small value.
If the readings are less than 300 μA, then a large resistance is connected in parallel to these two resistors. This will reduce the total resistance of the pull-up resistor.
This operation continues until the needle is at the 300 µA full scale, which signals a fine fit.
To select an accurate 97 kOhm resistor, select the closest one that is suitable for the nominal value, and do the same procedures as with the first 7 kOhm one. But since a 30 V power supply is required here, it will be necessary to rework the multimeter's power supply from 1.5 V batteries.
A block with an output voltage of 15-30 V is assembled, as long as it is enough. For example, it turned out 15 V, then the whole adjustment is made on the basis that the arrow should tend to a reading of 150 μA, that is, to half of the scale.
This is permissible, since the tester's scale is linear when measuring current and voltage, but it is desirable to work with full voltage.
DC current or voltage generators are required to adjust the 997 kΩ pull-up resistor for the 300 V range. They can also be used as attachments to a multimeter when measuring resistance.
Resistor ratings: R1 = 3 Ohm, R2 = 30.3 Ohm, R3 = 333 Ohm, R4 variable by 4.7 kOhm, R5 = 7 kOhm, R6 = 97 kOhm, R7 = 997 kOhm. Are matched by fit. Power supply 3 V. Installation can be done by hanging elements directly on the board.
The connector can be installed on the side of the box into which the microammeter is cut. The probes are made of single-core copper wire, and the cords for them are made of stranded wire.
The shunts are connected with a jumper. As a result, a tester is obtained from a microammeter, which can measure all three main parameters of electric current.
Having made myself a mini-tester, I have been using it for several years now in the repair of household electrical and radio equipment. Assembled according to the classical scheme, the device allows, with sufficient accuracy for practice, to measure voltages up to 300 V in DC and AC circuits, to check resistors, diodes, transistors and capacitors.
To manufacture such a mini-tester, a small number of radio components are required, and none of them are expensive and scarce. They are always, as they say, at hand, they can be easily found in stock at any radio amateur. And as a supporting structure, a circuit board and a device body ... the measuring head itself M42100 (or a similar type) is used, designed to measure a DC voltage of 3 or 30 V.
Miniature sockets are mounted on the head body. There are also "seats" for the screw MZ (the probe "General" is attached to it), the variable resistor R2 "Ust.O" and the flashlight FRM-1, which acts as a case for a power supply such as STs32, STs21, etc. If desired, you can add a phase indicator to the device (shown in dotted lines in the diagram) - there is enough space inside the head.
The scale "-30 V" is basic, it is taken ready-made. It is used to bind the divisions in the range with the upper limit "-300 V". And to measure alternating voltages(due to the nonlinearity of the initial section), as well as for measuring resistances, it is desirable to have additional scales. They are graded according to methods that are described in sufficient detail in the popular literature.
It is advisable to replace the glass in the tester with a plexiglass plate - it will not break when the device is hit or dropped.
V.REZKOV, Vitebsk, Belarus
Greetings, dear friends! In this article, I will show and tell you how to make a very simple tester for testing radio components such as diodes, transistors, capacitors, LEDs, incandescent lamps, inductors and much more. Especially novice radio amateurs will like this tester. Although, it is so convenient that experienced radio amateurs use it to this day.
Tester circuit
The tester contains the minimum number of elements that are sure to be found in the household even for novice radio amateurs. The whole circuit is essentially one multivibrator, assembled on transistors. It generates rectangular pulses. The monitored circuit is connected to the arms of the multivibrator in series with two LEDs, counter-parallel. As a result, the circuit under test is tested with alternating current.How the tester works for checking radio components
An alternating current is removed from the working multivibrator, which is approximately equal in amplitude to the power source. Initially, the LEDs are off because the circuit is open. But if you close the probes, then the alternating current will run through the LEDs. At this time, an alternating current with a frequency of about 300 Hz will run through the LEDs. As a result of the counter-parallel switching on, the LEDs will flash alternately, but due to the high generation frequency, this will not be visible to the human eye, but it will be seen that both LEDs are simply lit simultaneously.What does it do? - You ask. For example, if you connect a diode to the probes, then only one LED will light up, since the alternating current will run only after one period. As a result, it will be immediately clear that the connected diode is working properly. The same is observed when checking the transitions of the transistor.
The main convenience of this tester is that it can be seen immediately whether the diode transition is working or not. There is no need to turn the elements over to match the polarity of the tester, as in a conventional multimeter. This gives a huge advantage when checking a large number of radioelements, and in general it is very convenient.
You can also check for breakdown or breakage of other elements or circuits.
The tester can be assembled on the board or by surface mounting. It is better to take LEDs of different colors so that you can clearly see the work visually.
Also, with the help of this simple device, you can determine in no time where the cathode and anode of an unknown diode are. But for this it is necessary to mark the location on the LEDs of the tester.
As a power supply I used a 3.7V lithium-ion battery. But you can take 2-3 "little finger" 1.5V batteries connected in series.
In general, the thing is very necessary. I recommend that you repeat this non-tricky device. And the convenience in work is provided to you, since in most cases it is required to determine the serviceability of the radio element, and not its parameters.