Miniature Exam Device
Now having inserted the wiring of the coil into the holes of the base, the membrane is glued with a minimum of superglue to the outside of the case - the cylinder. Wiring soldered to the pads. At the same time, you should try not to overheat the earpiece in any other way, otherwise a magnet or something else might fall off. Now call with an ohmmeter and make sure that everything is in order of 20-80 Ohms.
A wireless headset for exams
This device was not assembled by necessity, but due to the absence of its circuitry in the network.
The receiver of the device is simple; it is a detector receiver with one cascade strong. The input circuit is composed of a resistor and a capacitor. The voltage induced in the circuit is detected by a diode and then amplified.the transistor in the collector of which the high-impedance earphone is installed and it is the load a small displacement of the base is achieved by a resistor whose resistance depends mainly on the coef fi cient of the base current amplification, its resistance can lie within 200-430 kOhm. Such a simple construction scheme provides high parameters with very small sizes. Transistor used domestic KT3130 when choosing a transistor should strive to maximize its amplification. The diode was taken flint with a Schottky barrier type KD514 or similar imported! Of course, it was better to apply germanium, but it was not possible to find miniature ones. Resistor RC0402 5% from 200 to 430m (pick up when tuning up to a maximal undistorted signal.In the circuit of the receiver any SMD throttle can be used I applied 1mkGn type SDR0402 type / size 0402 from Bourns SMD condenser type GRM size 0402 +/- 5% TKE MP0 The headphone type TEM-1957, TEM-1956, TEM-1958M, TEM-1958, TEM-2632 or any miniature main thing that its resistance was not less than 300 Ohms is better still higher. choose as small as possible from an electronic watch.But we should not forget that the less it is and the cheaper you get it, the less it will serve! Perhaps it will not be enough until the end of the exam. In the absence of miniature headphones, I can’t lay out the whole headphone design, although it’s not hard to guess, but soon they should appear then the article will be much more complete and not expensive self-assembly kits will appear! &Nbsp;Transmitter.
An offset voltage should be applied to the base of the T4 transistor resistor, it is omitted in the circuit. The 180 kΩ resistor from the power supply plus to the base of the transistor T4
ULF (T 1) and the modulator (T 3) do not need to be adjusted. Setting the master oscillator by changing the position of the trimmer common coil L 1, L 2 and changing the values of the capacitors C 6 to the maximum wavemeter. The next stage is L 3. It may be necessary to select the values of the 24k base resistor (transistor of the master oscillator).When tuning the antenna by changing the capacitors of the P-filter and adjusting the L 5, it is advisable to use a wave meter. When adjusting the output stage and its coordination with the antenna, it is advisable to take into account not the optimality of its length, which reduces the radiated power of the transmitter. Therefore, it is advisable (as in the previous case) to use additional inductance (although this is not mandatory), which increases the effective length of the transmitting antenna of the transmitter. This coil is connected in series with the antenna (not shown in the diagram). The parameters of the elements of the U-shaped filter (L 5) and the additional coil are the same as the parameters of the previous construction.
Wireless headset for exams
This radio headset differs from Variant 1 in all even the principle of operation. It works by using an inductive method. The coil that will be on your neck is the primary winding, and on the earpiece it is secondary. All other electronics are low-frequency amplifiers.Now, by construction.
We wind up the receiving coil with the TEM-1958 earphone; it contains 70-100 turns of enameled wire of the type PEV-2 0.05-0.07 thicker should not be used ( can not get into the ear). Radio parts used in the radio headphone can be seen in Fig. 1
All parts of the headphone can be mounted in two ways. The first and the simplest is a mounted installation, see fig. 2 and 3
Now we’ll look at the headset. It is assembled rather primitive and does not need any sort of adjustment, if assembled from previously functioning components. Refer to Fig. 4.
As you can see from the diagram, this is a normal low-frequency amplifier with a direct connection (links) the coil is connected via a coupling capacitor. All transistors in our variant were chosen by the enemy, mainly because of the miniature type SOT-323, they are called VS847.You can apply any other sound low-power even the structure does not matter only the size. (If the structure of the transistors changes, just change the polarity of the device's power.)
Transmitter antenna (see figure 5)
It is easy to make. A wire with a diameter of 0.33 mm or so. It is better to take a flexible mounting, than it will be softer, the better. Also need a shrink tube close to the color of clothing or body. But this is not necessarily just faded tones. On the mandrel (pot of pot or something else) we measure 20 cm in diameter by bending the heat shrink tube and cut it off. We also do it, I use a rocky wire about 1-2 mm thick and thread it into a therm tube and tie our wire to one end with any convenient method. It will be an improvised needle. Now measure a piece of wire, measuring its resistance, it should be about 16nnom. Now begin to pass the wire around the gap between the ends of the tube. When everything is ready you will get a ring with a diameter of 20 cm with at least 40 wires. We put the tube in warm air and clean the two ends by soldering to them a piece of shielded wire from the faulty headphones for the player, well, if the connector on the wire it, then come in handy,since it is possible not to assemble the amplifier, but connect the antenna to the player to the receiver and so on. At the junction (soldering) we put on a piece of tube 5-8 cm, taking into account that the tube closes the soldering and the folded two antenna coils are inserted into it. The transmitter of this antenna can be any audio power amplifier over 50 mW and capable of operating at a load of 8-16 ohms.
Printed circuit board of the second layout.
They did not finish the article to the end, but people are already muddling. They pass exams very well probably. Dmitry sent pictures of his device (see below).
Amplifier (Option # 1)
Transmitter amplifier number 2. It doesn't get any easier. The difference is that you have to wind the coil on the resistance indicated in the diagram. (instead of dynamics)
Wireless earphone for exams(Option 2 - continued)
How to make an amplifier (transmitter) :
1). We buy ordinary Chinese radio with automatic tuning, without dynamics. Any model will do as the scheme is practically the same.
2). Parse the radio.
a). We find the chip. Carefully remove 2, 4, 5 legs. (If you look at the chip from above, and assume that the first leg is next to the label).
b). Find the headphone jack. We find the foot of the socket, which gives a signal to the middle contact of the plug (if the plug is stereo). We find the path that comes from this leg and cut it. Generally the socket will be adapted for a mono plug. There will be stuck an antenna worn around the neck.
c). Find a variable resistor, which is a volume control and a switch. The two outermost contacts go to the hundsfree instead of the headset (see photo_1).
3). We cut a place for the hundsfree wire in the radio case. We close everything as it was in the case. Amplifier is ready to eat! (see photo_1)
We connect the phone to the hundsfree (the hundsfree should answer the phone!).In the amplifier (former receiver), instead of headphones, we plug the antenna.
Hundsfree doesn't need much refinement! Instead of a headphone we connect the amplifier. You can open the hundsfree button and pull out the microphone from there. Make it on a separate wire (see photo_1). The most important thing is that the hundsfree should be chosen for a specific phone model. Otherwise there may be problems with the sound.
The headphone coil is wound right on the phone capsule (TEM) along it! After winding, it is convenient to fix the coils on the primer with super glue. Headphone parts are mounted on the board, which simplifies the assembly process and allows you to solder chip parts of size 0805 and smaller. The place for the battery is located behind the earphone. The board is located above the battery. Headphones are obtained from one end of a bit thicker, which holds it well in the ear and does not allow it to get into the brain! : 0)
Contacts for the battery are cut from the copper screen (from some kind of coil) and soldered to the board. A cap with a coil wound on it can also be glued with a super glue to one of the battery contacts (through the gasket). All systems are shipped in a shrink tube diameter 9-10 mm.and with the help of a building hair dryer or an ordinary candle, it is gently adjusted to the ready state (the battery should be inserted into the earpiece and the tube on the wide side of the earpiece should be clamped with tweezers, after cooling down, a beautiful seam is formed in the clamped area, which can be trimmed with nippers). See the photo.
I wanted to add it especially for crazy pens! In order not to buy or break a receiver even if it is Chinese, let's turn to its scheme. see below
From it we see that most of it is not used, but only the AF amplifier assembled on two transistors is used! We can replace them with domestic ones, for example, KT3102. It will not be worse, and maybe better. This amplifier is capable, with distortions, to give away power that will be sufficient for high-quality earphone operation. But there are pitfalls, this scheme will not provide high-quality sound and it will be at the level of industrial designs! But we are lovers of radio and will not stop at what has been accomplished.
Amplifier AF is better quality can be assembled on one cheap chip and four discrete elements. I hope no need to explain what we turn on instead of headphones? Yes, correctly, the transmitter coil is sluggishly hanging from the neck.="">
Here we come to the final part of the article. And we put a bullet on this.
A wireless headset for exams
(Option 2 - ending)
The radio headset, the assembly of which will be discussed, is assembled according to the scheme (Fig. 1), which was previously presented. To do this, we will need all the radio components (SMD) shown in the diagram, the TEM-1958 electromagnetic telephone, the heat shrink tube (preferably in flesh-colored) and the enameled wire of 0.04-0.05 mm (you can get it by breaking the Chinese alarm clock).
First of all we make a printed wiring diagram on a computer becauseitisreadythenjustdownload,printandmaketheboarditself.
The layout of printed montage, as seen in the figure, consists of two separate parts. On the main board are located: transistors V1-V3 and resistors 10K and 43K. On the second board are: 0.1mF capacitor and 560K resistor.
Since the radio headset must be as compact as possible, therefore, you must also make the board with the utmost care. In order for the boards cut in this way to be not only small in area (Fig.6), but also in thickness, we start very carefully and painstakingly grinding the surface of the board from the reverse side, and for one also nails. For a start, it is best to use a large sandpaper well, and only then when the reverse surface is ground to a minimum (the main thing here is not overdone!) We take as small sandpaper as possible and gently modify the surface, remembering that with this surface both boards will be glued to the TEM case -1958.
Then, as expected, the soldering of elements follows.Solder best on some kind of metal surface, which will absorb excess heat, because when soldering on so much thin boards can go off the track! (well, however, it all depends on your ability to solder). We stick the finished boards with a reliable superglue so that the boards fit together (Fig.9), we solder the junction point (just the place where the capacitor is connected to the emitters of the transistors). The protruding edges are removed with a scalpel!
Now we take the coil (Fig.10) with the previously mentioned enameled conductor and wind 70-100 turns on the remaining free space on TEM-1958 and according to the scheme we solder its ends to the boards. For reliability, you can drop a bit of glue onto the reel. Using a conductor with a larger diameter can lead to self-excitation of the earpiece (high-frequency squeak).
If the workpiece looks like this, then you are in the right direction!
We use tin (can be removed from the old battery) and the material for the manufacture of boards to make a battery fusng. Cut out the main part of the body from the tin (which is also a “+”), see figure 12, cut a circle with a diameter of 6 mm from the material for making boards, and again take a nazhdachka and grind the surface and, without that, bleeding, fingers to a minimum, This is how we got the clams "-". As a result, the Fassung looks the same way. fig.13.
Now comes the very crucial moment of “Installing the Fasung”. If you do not concentrate now, then consider the matter failed! First of all, we solder the Clamp “+” to one of the TEM-1958 contacts (better to the right, when viewed from the marking side and considering that the contacts are on top), this should be done very carefully and quickly, because these contacts disappear very quickly and then everything , "Hemorrhoids"! Well, if everything worked out, then we can continue further, so that this terminal will no longer disappear and spoil your mood,then it needs to be properly glued or poured with a two-component superglue (its durability is 250kg / cm ?, it is possible and weaker), at the same time we glue the terminal "-" (But before that, do not forget to connect the second TEM contact with the circuit, otherwise it will be too late!) Clem " + "Should not come into contact with the body!" After the glue dries well, , we add, according to the scheme, the missing connections, for this we use an enamelled conductor. In places where it will pass, spill a moderate amount of Chinese glue second, so as not to perekknulo (isolation). In the end, the resulting construction is placed in a heat shrinkable tube (the battery must be in the fungus!), Heated with a building dryer or a lighter, from the battery side we clamp the heated tube with tweezers, carefully sticking out the extremities with a scalpel. A properly assembled headphone will emit a slight hiss!
So it looks in the ear!
Making a transmitter antenna is set out in previous articles!Goodlucktoall!!!!
Wireless micro earpiece on a microcircuit
Gathered for this exam all this setup on the TDA7050 chip, both the amplifier for the loop and the headset itself.
For a loop, I used a chip in a regular package. The circuit is similar to the stereo (bottom), only connected together 2nd and 3rd legs, and 7 and 8 separately go to the capacitors. But after them, not on 2 speakers, but connected together on a loop (purely by ear, so the sound is more powerful than using the mono-variant, ie, the upper 1st circuit), the second end of the loop is naturally minus.Ialsoused361Abatteries,theyareindiametersameasLR41butthinner.361Alastsapproximatelyatleast1.5hours,Icannotsayforsure,Icheckeditwitholdbatteries.Thecurrentbetweenthemandtheearisabout5-6mA(ifmeasuredwithacheapoldChinesetester).Butaccordingtothemanualforthemicrocircuit,itiswrittenthatat3Vthecurrentconsumptionis3.2mA.Asfornoise,speechandmusicintheearphonecanbeheardanddisassembled,butthefewerturns,thelessaudible,butlesshissing.Themoreturns,thebetteryoucanhearboththespeechandthehiss,thoughthereisacertainlimit,whenitisexceeded,thespeechbeginstodisappearandthehissandsensitivitytoallkindsofinstrumentsincreaseevenmore.Youcan,leaningyourearagainstthewall,todeterminewithoutanyproblemswherethewiringpasses.
I loop the loop by 32 ohms. As a battery, I took the battery from Samsung X100.
If there is a possibility, it is better to assemble the amplifier for the loop using m / s TDA7052, the earphone catches a lot better!
I used a microcircuit in the SMD package in the earpiece itself. The speaker took from Nokia (the one that seems to be 60 ohms). Collected according to the first scheme, but only without any resistors and capacitors, i.e.I connected the coil to the input (without capacitors and resistors !!!), which I wound on the microcircuit.
And to have more resistance, I simply wound more turns (minutes 12 -13 was wound by hand with a wire of 0.01 mm, until the wire itself broke, at this place and attached to the minus).
I used two LR41 batteries (such but fit). And so well learned, for me the best option, because I do not sell small parts in my city at all, I did not immediately find a microcircuit. The size of the “ear” is in principle normal, but let's say it wouldn't fit in my classmate.
Here are the pictures, though they are draft versions (paper body, so that would somehow keep the batteries), tk. I haven’t yet found the shrinkable tube of the required diameter.
Well, that's what under the piece of paper, of course, you need to do more tightly
>div style="text-align: left;">Perhaps the most important part: the coil is wound directly on the microcircuit attached to the speaker. All 45 soldering tools were soldered. There is nothing particularly complicated and small details too: only the microcircuit and the speaker from the Nokia, well, the coil is natural.Ofcourse,ifitismorecarefultodoeverythingandputlessbatteries,thenitcanstillbewoninalengthof1-1.5mmandindiameterintheareaofbatteries.Onlythediameterofthespeakercannotbechanged,ifonlythespeakerisfoundsmaller.Myversioninlengthturnsout9mmtogetherwithbatteries.Thediameterintheareaofthespeakeritselfis8mm,wherethebatteriesareupto8mm(dependingonwhichbatteriestoput).
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