Homemade mini tester with your own hands. Tester from a smartphone. What capabilities does a smartphone tester provide?
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. Beginner radio amateurs will especially like this tester. Although, it is so convenient that experienced radio amateurs still use it to this day.
Tester circuit
The tester contains a minimum number of elements that even novice radio amateurs will definitely find in their household. The entire circuit is essentially one multivibrator assembled using transistors. It generates rectangular pulses. The controlled 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.Operating principle of the tester for checking radio components
Removed from the working multivibrator AC, approximately equal in amplitude to the power source. Initially, the LEDs do not light up because the circuit is open. But if you short the probes, then alternating current will flow through the LEDs. At this time, an alternating current with a frequency of approximately 300 Hz will flow through the LEDs. As a result of back-to-back switching, the LEDs will flash alternately, but due to the high generation frequency, this will not be visible to the human eye, but will be visible that both LEDs are simply glowing at the same time.What does this give? – You ask. For example, if you connect a diode to the probes, only one LED will light up, since the alternating current will flow only after one period. As a result, it will immediately be clear that the connected diode is working. The same thing is observed when checking transistor transitions.
The main convenience of this tester is that you can immediately see whether the diode junction is working or not. There is no need to flip the elements to match the polarity of the tester, as in a conventional multimeter. This gives a huge advantage when testing a large number of radio elements, and is generally very convenient.
You can also check other elements or circuits for breakdown or breakage.
The tester can be assembled on a board or mounted. It is better to take LEDs of different colors so that the work can be clearly seen visually.
Also, using this simple device, you can quickly determine where the cathode and anode are on an unknown diode. But to do this, you need to mark the location on the tester LEDs.
I used lithium as food ion battery voltage 3.7 V. But you can take 2-3 “pinky” 1.5 V batteries connected in series.
In general, this is a very necessary thing. I recommend that you repeat this simple device. And you are guaranteed ease of use, since in most cases you need to determine the serviceability of the radio element, and not its parameters.
Watch a video on working with a tester to check radio elements
Despite the high reliability of the auto electrics of modern cars, you still have to deal with its repair. Most often, lighting devices, headlights, side lights or direction indicators stop working. The cause of the malfunction may be the light bulb itself, or the current-carrying contacts or fuse. All three faults may occur at once. Due to poor contact in the socket or socket of the light bulb, it may burn out. At the moment of burnout, an arc occurs in the light bulb itself, shortening the filament, which leads to a sharp increase in current in the circuit. When a light bulb burns out, the fuse often blows too.
It’s impossible to figure out the cause of the breakdown without instruments. simple task. You will have to substitute known good parts. The malfunction can be determined using a dial tester or multimeter, but not everyone has such a device and it is not very convenient to work with it in a car, especially in bad weather. It is much more convenient to look for a fault with the simplest universal car tester-probe, made by yourself.
A car probe tester can be made from any ballpoint pen by removing the writing core from it and placing in its body just one LED of any type and a current-limiting resistor. The parts are connected to each other according to the electrical diagram below. schematic diagram. As you can see, simpler than the diagram doesn't happen. Any car enthusiast who has no experience in making electronic devices can make such a probe with his own hands.
For reliable electrical contact when touched by the probe and the possibility of puncturing wire insulation when troubleshooting, the end of the probe is made in the form of a steel tip. To make such an end from a writing rod, you need to remove the writing unit and insert a thin sewing needle into it from the side where the paste arrives. The needle will squeeze out the ball, and its sharp end will come out of the writing unit. If you insert it with considerable force, it will be firmly fixed. A conductor leading to the LED is soldered to the needle itself.
The writing rod must be taken with a brass writing unit and a large ball (pens with such rods are left wide line), otherwise the needle may not enter the writing unit sufficiently and will not protrude sufficiently, by 1.5-2 mm.
The conductor for connecting the car tester to the negative of the battery or the car body can be soldered directly to the terminal of resistor R1. But to be able to change the conductor in case it breaks or if a longer wire is required, I connected it on a thread.
To do this, it is enough to fuse a piece of tube with an internal thread, heating it with a soldering iron, into the prepared hole in the body of the pen, having previously soldered a conductor of the required length to it.
The LED is installed on the side of the body of the car tester, but you can install it on the end of the body and bring the negative wire out to the side.
How to use the tester
I will give examples of how you can use a tester to check the serviceability of a battery, fuse, incandescent light bulb and electromagnetic relay.
How to check the battery
To check the presence of voltage at the battery terminals, you need to connect the alligator clip to the negative terminal of the battery, and touch the positive terminal with the end of the tester probe.
How to check a fuse
How to check an incandescent light bulb
To check an incandescent light bulb with a tester, you need to touch one terminal of the light bulb base to the positive terminal of the battery, and touch the second terminal of the light bulb with the probe of the tester.
If the LED lights up, then the bulb is working. If there are two filaments in a light bulb, for example a car headlight bulb, then the filaments are checked one by one.
How to test a car relay
In addition to the electromagnet winding, an automobile relay also has contacts, which burn out over time and may stop switching electrical circuits. Using a tester, you can check both the integrity of the winding and the serviceability of the contacts.
Standard automotive relay has below electrical diagram. Terminals 85 and 86 are made from the relay winding. The output numbered 30 is made from a moving contact, 87a is from a normally closed contact with moving contacts 30 and 87, this is the output from the contact to which moving contact 30 is connected when supply voltage is applied to the winding.
To check the relay winding, you need to touch one of its terminals 85 or 86 to the positive terminal of the battery, and touch the second terminal with the tester probe. If the LED lights up, it means the winding is intact. The serviceability of the contacts is checked by touching the terminal of the moving contact 30 to the battery terminal, and the probe to terminal 87a. In the same way it is easy to check any switches and microswitches.
How to use the tester
when repairing car electrical wiring
In practice, when troubleshooting a car's electrical equipment, there is no need to remove fuses and light bulbs. As you know, the negative terminal of the battery is connected to the body of the car and all electrical equipment in the car is also connected to the body with one terminal. Thus, it was possible to halve the number of electrical wiring wires and increase its reliability. The only exceptions are activators for car door locks, since they need to be supplied with voltage of different polarities depending on the need to open or close the door lock.
For example, if one of the headlights does not light. The malfunction may be in one of the elements supplying voltage to the light bulb - a switch in the cabin, a relay, a fuse, or a malfunction of the light bulb itself. Most likely the light bulb itself has burned out, and that’s where you need to start checking.
To do this, use the alligator clip of the tester to grab onto any exposed metal part of the car body or the negative terminal of the battery. Check the quality of the contact by touching the probe needle to the battery positive. The LED should light up. Turn on the idle headlight and use the end of the probe to touch all the light bulb connection contacts one by one. If this is not possible, then you can use a probe needle to pierce each wire in turn, and if there is no voltage on any of them (the probe LED does not light up), then the light bulb is intact, and you need to check the fuse.
Use the diagram to see where it is installed and check it without even removing it from the block. To do this, just touch first one of its conclusions, and then the other. The tester LED should light up every time. If it only lights up when you touch one of the terminals, then the fuse has blown. If you cannot get to the fuse terminals, you need to remove it and check it, as described in the article above.
Using this method, any electrical wires and contacts in the car are checked.
In this article I will tell you how to make a dial tester out of a smartphone. electrical circuits for a break or short circuit. In fact, I'll make a console for cell phone(rather, even an adapter with probes), with which you can take measurements. Its circuit is incredibly simple and contains one resistor.
This craft may come in handy if your working multimeter is broken. Or you don't want to take it with you. Personally, I made such an adapter-attachment and threw it in the glove compartment of the car. Now, when I need to ring a light bulb, fuse or something else, I take out the probes and connect them to the phone.
What capabilities does a smartphone tester provide?
With this tester you can:- - Check the circuit for an open or short circuit.
- - Find out the approximate resistance value (0-70 Ohm).
- - The smartphone makes a sound when continuity is detected.
Adapter-attachment diagram
Pinout of headset jack pins.We will feed the signal from the probes to the microphone input.
Everything can be done by surface mounting by soldering a resistor to the plug, soldering the wires and filling the whole thing with hot glue. Or make a separate unit with a split for the probes, put on heat shrink and blow it off. As a last resort, use electrical tape. 15 minutes of work, no more...
Smartphone app
After the adapter is soldered, download the application from (active link to the application) and install it.Launch the application and connect the adapter. Everything should work. If you close the probes, you will hear a beep, which means everything is fine and you can use it.
Initially zeros are shown:
And when you close the probes together, this word appears and the phone beeps.
Caution when using the tester
This tester cannot measure circuits where there is voltage! Because your smartphone may fail. Also keep in mind that in some circuits there may be residual voltage on the device’s capacitors, which will also be dangerous for the smartphone.Sometimes a thing is very necessary and useful in the household.
Smartphones have long been part of our lives and are being used more and more.
Those who like to do it themselves are offered a simple tester based on the M2027-M1 microammeter, which has a measurement range of 0-300 μA, internal resistance of 3000 Ohms, accuracy class 1.0.
Required Parts
This is a tester that has a magnetoelectric mechanism to measure current, so it only measures DC current. The moving coil with an arrow is mounted on guy wires. Used in analog electrical measuring instruments.
Finding it at a flea market or buying it at a radio parts store won’t be a problem. There you can also purchase other materials and components, as well as attachments for the multimeter. In addition to the 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.
Selecting measurement ranges and calculating resistor values
Let us determine the range of measured voltages for the tester. Let's choose the three most common ones, covering most of the needs of radio amateurs and home electricians. These ranges are from 0 to 3 V, from 0 to 30 V and from 0 to 300 V.
The maximum current passing through a homemade multimeter is 300 μA. Therefore, the task comes down to selecting an additional resistance at which the needle will deflect to full scale, and a voltage corresponding to the limit value of the range will be applied to the series circuit Rd + Rin.
That is, on the 3 V range Rtot=Rd+Rin= U/I= 3/0.0003=10000 Ohm,
where Rtot is the total resistance, Rd is the additional resistance, and Rin is the internal resistance of the tester.
Rd = Rtot-Rin = 10000-3000 = 7000 Ohm or 7 kOhm.
On the 30 V range the total resistance should be 30/0.0003=100000 Ohm
Rd=100000-3000=97000 Ohm or 97 kOhm.
For the 300 V range Rtot = 300/0.0003 = 1000000 Ohm or 1 mOhm.
Rd=1000000-3000=997000 Ohm or 997 kOhm.
To measure currents, we will 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. That's why
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.
From here in the range 0...3 mA
Rtotal=U/I=0.9/0.003=300 Ohm.
Then
Rsh=Rtot*Rin/(Rin-Rtot)=300*3000/(3000-300)=333 Ohm.
In the range of 0...30 mA Rtot=U/I=0.9/0.030=30 Ohm.
Then
Rsh=Rtot*Rin/(Rin-Rtot)=30*3000/(3000-30)=30.3 Ohm.
From here, in the range of 0...300 mA Rtotal=U/I=0.9/0.300=3 Ohm.
Then
Rsh=Rtot*Rin/(Rin-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. Let's prepare the board for installation. To do this, you need to draw it into squares measuring a centimeter by a centimeter or a little smaller.
Then, using a shoemaker's knife or something similar, the copper coating is cut along the lines to the fiberglass base. Turned out to be isolated contact pads. We noted where the elements would be located, and it looked like a wiring diagram right on the board. In the future, tester elements will be soldered to them.
In order for a homemade tester to give correct readings with a given error, all its components must have accuracy characteristics that are at least the same, or even higher.
We will consider the internal resistance of the coil in the magnetoelectric mechanism of the microammeter to be equal to 3000 Ohms stated in the passport. The number of turns in the coil, the diameter of the wire, and 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 battery voltage
In order to find out the actual battery voltage 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 because when a microammeter is connected in series with it, the total resistance of the circuit will be 5000 Ohms. Consequently, the current passing 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 of the shunts and additional resistors.
Assembling the power supply
The power supply for the multimeter is assembled from two 1.5 V batteries connected in series. After this, a microammeter and a 7 kOhm resistor pre-selected at 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 a second, small value resistor must be connected in series to the first resistor.
If the readings are less than 300 μA, then a high-value resistance is connected in parallel to these two resistors. This will reduce the total resistance of the additional resistor.
Such operations continue until the needle reaches the scale limit of 300 μA, which signals an accurate fit.
To select the exact 97 kOhm resistor, select the closest one that matches the nominal value, and follow the same procedures as with the first 7 kOhm. But since a 30 V power source is required here, the multimeter’s power supply will need to be reworked from 1.5 V batteries.
A unit is assembled with an output voltage of 15-30 V, as long as it is enough. For example, if it turns out to be 15 V, then all adjustments are made on the basis that the needle should tend to read 150 µA, that is, half the scale.
This is acceptable, since the tester scale when measuring current and voltage is linear, but it is advisable to work with full voltage.
To adjust the additional resistor of 997 kOhm for the 300 V range, generators will be needed DC or tension. They can also be used as attachments to a multimeter when measuring resistance.
Resistor values: R1=3 Ohm, R2=30.3 Ohm, R3=333 Ohm, R4 variable at 4.7 kOhm, R5=7 kOhm, R6=97 kOhm, R7=997 kOhm. Selected 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 wall of the box into which the microammeter is embedded. The probes are made of single-core copper wire, and the cords for them are made of stranded copper wire.
The shunts are connected using a jumper. As a result, a microammeter turns into a tester that can measure all three main parameters of electric current.