What can be made from a radiotelephone handset. Electrical diagrams for free

Articles and Lifehacks

A smartphone is a multifunctional phone, the capabilities of which go far beyond “just making a call,” so the question of how to make a walkie-talkie out of a phone can be completely solved today thanks to many applications.

It would seem, why make a walkie-talkie out of a fully functional phone if you can’t use other features in this mode? But this device has a number of advantages:

the ability to communicate with many people at the same time;
a closed communication channel that is completely inaccessible for listening;
no tariffs for call duration, etc.

What programs can you use?

There are many mobile applications that allow you to simulate the operation of walkie-talkies. Some of them are very popular and have many advantages, others are less interesting, but are attractive due to their ease of use or lack of fees.

So, first of all, programs distinguish between paid and free.

The former, as a rule, pay the operator, while the latter work for free via mobile Internet or Wi-Fi. Another important difference is the platform on which the application runs.

Most are written for Android and iOS, but there are also those that work on the old Symbian, and there are even walkie-talkies that are provided by telecom operators, so they will be useful for any phone model.

Which program to choose

To begin with, it is important to understand not the principle of implementing this process, but which program to choose. So, if your smartphone runs Android and iOS, you can choose between Zello and Voxer.
The first allows 800 devices to work simultaneously (for comfortable use, it is better to reduce the number to three hundred), connecting via the Internet, you can also use it from a tablet and PC.
It is also compatible with Bluetooth headsets, has high channel protection and other properties.
The second can already unite only 100 people via the Internet and is used only on phones. But it already transmits photos and other media, allows you to save recordings, use it offline and then send it over the network.
For Symbian, Walkietooth and Push-To-Talk are recommended. The first one is quite old, but works offline.
It unites only two people, and the message can only be 10 seconds long, but this is an indispensable option in conditions where there is no connection.
The second one already uses the Internet and is more interesting in terms of functions.

Thus, a mobile walkie-talkie is a very useful feature that can be used and be relevant today.

Sometimes it happens that a home radiotelephone becomes obsolete and ceases to please you as much as before - after all, modern models appear that you want to “insert” into your interior for the joy of yourself and your loved ones. It also happens that he is overtaken by a local malfunction; for example, my Texet TX-D5300 phone, after falling to the floor, stopped displaying some symbols on the display, and reading information turned into torture for me. Disassembling the device and improving the contacts between the display and the printed circuit board yielded nothing. Unfortunately, there are hundreds and thousands of such and similar cases. The small (up to 1000 rubles) cost of such “toys” suggests that the owner will replace such a phone without regret, since the profitability of the repair will outweigh the cost of the product itself.

Nevertheless, household radiotelephones with minor and local faults are quite suitable for breathing “new life” into them with the hands of a radio amateur.

For example, it’s not at all difficult to make a remote signaling device for opening the front door out of a “toy”; and this task skillfully translated into reality will allow you to go even further and notify with sound about any other (with appropriate connection) change in the controlled parameter within the same apartment (office). The main thing is that the transmitting and receiving paths are working properly and the “handset search” function is working. Next, I will tell you how to turn such a semi-functional wireless kit into a useful household item.

In Fig. Figure 3.29 shows the appearance of the Texet TX-D5300 wireless kit, consisting of a base and one handset.

To modify the basic (standard) kit (base + handset), you will need to take a few simple steps. Here they are:

Disassemble the base of the radiotelephone (remove the housing to access the printed circuit board);

Connect a two-wire cable with a maximum length of no more than 1.5 m parallel to the contacts of the “tube search” button (to avoid false positives from alternating voltage interference from network wires);

Connect the other end of the cable to a limit switch (for closing) or a reed switch for opening (with a normally closed group of contacts) installed on the front door frame (see details below);

Install (fix) the radiotelephone base here, not far from the “remote switch”;

Using a standard adapter, connect the base to a voltage of 220 V;

Connect the remote handset to another (additional) network adapter with an output voltage of 3-5 V, so as not to depend on the discharge of batteries or batteries in the handset;

Place the handset with the adapter in the desired location, for example, not far from the desktop.

Let's look at these steps in more detail.

In Fig. 3.30 shows a view of the base with the housing cover removed.

In the center of the printed circuit board (as can be seen in Fig. 3.30) there is a microbutton with short-circuit contacts; it has 4 pins, two of which are connected (duplicate each other). Using an ohmmeter, we check the connection in the contact group of the button - when you press it, we identify the closing contacts. In parallel, with a soldering iron with a thin tip and a power of up to 25 W (so as not to damage the radio elements on the printed circuit board), we solder a two-wire cable; there is no need to shield it (see Fig. 3.31).

The connection diagram is quite simple, and, in my opinion, does not even need to publish a separate drawing. This is a reed switch connected parallel to the “tube search” button (on the base).

More recently, LEDs were considered a novelty, but now they are widely used for additional lighting and room decoration. LED strip is widely used to create exclusive lighting solutions by designers...

In accordance with state regulations, in enterprises with hazardous work conditions, lighting equipment with an increased explosion protection class must be used.

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Hello, dear lovers of experiments and DIY experiments!

We have already touched on the topic of telephone communication on the pages of the DIY science and technology blog. Back then we were talking about a phone made from plastic cups. Unfortunately, such a telephone demonstrates very well some of the laws of acoustics, but in practice it can only be used in fairly ideal conditions - the telephone thread must be taut and must not touch any obstacles. Yes, and the length of the thread is limited. Another thing is a regular wired telephone. There is no doubt about its applicability. Despite the spread of mobile communications, it will not soon be forced out of apartments and offices. We’ll talk about it, and at the same time we’ll build our own simple telephone network, devoid of the above-mentioned disadvantages.

Did you know that telephone communication officially dates back to the 19th century, and since then the basic design of the telephone has remained virtually unchanged? This is true. Of course, the phone has changed in detail - a modern telephone includes electronic components that simply did not exist at the time of its invention. In telephone networks there are automatic telephone exchanges that switch subscribers among themselves. Various telephone services have appeared. However, the purpose of a telephone set of any circuit has remained unchanged since its invention by Alexander Bell in 1876 - converting sound into an electrical signal and transmitting it along a communication line to the desired subscriber and converting it back into an audio signal. And in this classic telephone connection there is no equal.

To demonstrate this point, let's compare the above-mentioned plastic cup phone to a regular telephone network. We have already talked about the disadvantages of the first - it is a short range, the absence of obstacles in the path of the communication line, and ensuring thread tension. In addition, let's estimate the speed of sound propagation in the first and second types of communication. Thus, the speed of propagation of a sound wave in iron is approximately 5000 meters per second. Even if we found a way to eliminate sound wave attenuation, sound from, say, Moscow to Vladivostok would take 30 minutes! I don’t know about you, but I would quickly get tired of such a phone - the radio signal reaches Mars faster! Another thing is the speed of propagation of an electrical impulse - 300,000 kilometers per second. There is no better intermediary for sound transmission. You just need to come up with a way to convert a sound wave into an electrical signal and vice versa. And this is exactly the method that Alexander Graham Bell found.

In his telephone set, the sound signal was converted into electrical impulses, which reached the opposite device through wires and were converted there back into a sound signal. Everything turned out to be as simple as it was ingenious! Of course, the first telephone network had no telephone exchanges, no dialers, or other modern telephone delights. There were only two telephone sets connected to each other by an electric wire. I suggest you check the possibility of the existence of such a telephone network. Moreover, it is quite possible to use such a telephone connection in practice, for example, to install telephones in a home workshop. And if you take such a phone to your child’s place of play, it will remain a key link in many games for a long time.

So, we will need:

two telephone sets;
electrical wire.
DC source.
telephone patch cord.

As for the electrical wire - there is no need to limit yourself - any length of telephone wire can be used for your experimental or home needs. The type of wire can also be almost any. In my experiments I used 30 meters of twisted pair cable.

As for the DC source, we can say the following. In the telephone network, the voltage on the line at rest (when the phone is on-hook) is 60 volts. But for our experiments, the voltage from two Krona batteries will be sufficient. You can also use a 12-20 volt power supply.

Take the patch cord and cut it in half.

We clean the ends. The strands of the patch cord are often very thin, and it can be inconvenient to simply strip them with a knife. You can burn them.

If you use batteries, connect them in series. It is convenient to use clip-on contacts, but you can do without them.

We connect our current source to the circuit in series, that is, to the break of one of the wires.

Don't forget to insulate the contacts.

That's it, you can use it! The only significant drawback of this scheme is the inability to call a subscriber. To ensure this possibility, it is necessary either to supply alternating voltage to the line, as is done in city networks, or to install an additional line to provide sound or light calls.

Electronic tricks for inquisitive children Andrey Petrovich Kashkarov

3.7. Control using an old radiotelephone or unusual use of the radiotelephone base and handset in everyday life

Sometimes it happens that a home radiotelephone becomes obsolete and ceases to please you as much as before - after all, modern models appear that you want to “insert” into your interior to the delight of yourself and your loved ones. It also happens that he is overtaken by a local malfunction; for example, my Texet TX-D5300 phone, after falling to the floor, stopped displaying some symbols on the display, and reading information turned into torture for me. Disassembling the device and improving the contacts between the display and the printed circuit board yielded nothing. Unfortunately, there are hundreds and thousands of such and similar cases.

The small (up to 1,000 rubles) cost of such “toys” suggests that the owner will replace such a phone without regret, since the profitability of the repair will outweigh the cost of the product itself.

Nevertheless, household radiotelephones with minor and local faults are quite suitable for breathing “new life” into them with the hands of a radio amateur.

For example, it’s not at all difficult to make a remote signaling device for opening the front door out of a “toy”; and this task, skillfully implemented in reality, will allow you to go even further and notify with sound about any other (with appropriate connection) change in the controlled parameter within the same apartment (office).

The main thing is that the transmitting and receiving paths are working properly, and the “handset search” function is working. Next, I will tell you how to turn such a semi-defective wireless kit into a useful household item.

To modify the basic (standard) kit (base + handset), you will need to take a few simple steps. Here they are:

– disassemble the base of the radiotelephone (remove the housing to access the printed circuit board);

– connect a two-wire cable with a maximum length of no more than 1.5 m parallel to the contacts of the “handset search” button (to avoid false positives from AC voltage pickups from network wires);

– connect the other end of the loop to a limit switch (for closing) or a reed switch for opening (with a normally closed group of contacts) installed on the front door frame (see details below);

– install (fix) the radiotelephone base here, not far from the “remote switch”;

– using a standard adapter, connect the base to a voltage of 220 V;

– connect the remote handset to another (additional) network adapter with an output voltage of 3–5 V, so as not to depend on the discharge of batteries or batteries in the handset;

– install the handset with the adapter in the desired place, for example, not far from the desktop.

Let's look at these steps in more detail.

In the center of the printed circuit board there is a micro-button with short-circuit contacts; it has 4 pins, two of which are connected (duplicate each other). Using an ohmmeter, we check the connection in the contact group of the button - when you press it, we identify the closing contacts.

In parallel, with a soldering iron with a thin tip and a power of up to 25 W (so as not to damage the radio elements on the printed circuit board), we solder a two-wire cable; there is no need to shield it.

The connection diagram is quite simple, and, in my opinion, does not even need to publish a separate drawing. This is a reed switch connected parallel to the “tube search” button (on the base).

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When starting work on this radiotelephone, I was given the task of creating a design that was simple to build and reliable in operation. As a result, a simple and economical radiotelephone was created, consisting of a handset and a base unit connected to a telephone line. Duplex communication between them is carried out in the range of 40...48 MHz at a distance of up to 300 meters in urban conditions, which allows you to set up a radiotelephone using a VHF receiver, the description of which is published in. The circuit is extremely simple and highly reliable, does not contain scarce parts, and is easy to manufacture and set up. This circuit is a continuation of the previous version of a simple radiotelephone. The main difference is quartz frequency stabilization and increased power of the transmitting path. These improvements made it possible to create the simplest radiotelephone, which is not inferior in its characteristics to some industrial products.

Technical characteristics of the radiotelephone

Radius of action, m................................................... ....... 200...300

Frequency of the receiving and transmitting path, MHz.........40...48

Frequency spacing not less than, MHz...................................................3

Sensitivity of the receiving path, µV............................3...5

Power of the transmitting path, no more than, mW...................20

Operating mode................................................... ........duplex

Modulation................................................. ........................... World Cup

Frequency stabilization.............................................quartz

Frequency deviation, kHz................................................... ............10

Control signal modulation...................................AM

Control signal modulation depth, %...................100

Tube current consumption no more than, mA....................................30

Base consumption current in standby mode, mA......6...8

Tube and base supply voltage, V...................................5

Telescopic tube antenna, cm........................30...50

Telescopic base antenna, cm....................................100

Operating principle of a radiotelephone

The operating algorithm of the radiotelephone is fully consistent with the operating algorithm of a regular telephone.

Structural diagrams of the tube and base are shown in Fig. 1 and fig. 2. The operation of the radiotelephone is based on the method of interrupting the carrier frequency of the master oscillator. The schematic electrical diagram of the tube is shown in Fig. 3, and the bases are in Fig. 4. In standby mode, only the receiver on the DA1 chip works in the base. When a call signal arrives via the telephone line, the ringing device in the base on the VTZ transistor, operating at the resonance of the ZP piezoelectric emitter, is activated.

When the tube is turned on, the transmitter on transistors VT1 ... VT2 emits a carrier frequency, which is received by the base receiver on the DA1 chip. The presence of a carrier frequency is detected by the silent tuning system of the BSN of the base receiver, which opens the key on the DA2 chip, turning on the base transmitter on transistors VT1 ... VT2. This is how the telephone line is occupied. It remains in this state as long as the handset is on. In the base unit, the VD1 LED and the VD2 zener diode serve as a transmitter voltage stabilizer and at the same time a busy line indicator. The base transmitter is powered entirely from the telephone line, which simplifies the design of the radiotelephone, making it more economical.

When transmitting information, modulated by the amplifier on the DA2 chip, the RF signal from the tube transmitter on transistors VT1...VT2 goes on the air. The base receiver on the DA1 chip receives it and converts it into a low-frequency signal, which, through the public key on the DA2 chip, which acts as an amplifier, enters the telephone line.

Rice. 1. Structural diagram of the tube

Rice. 2. Block diagram of the base

Rice. 3. Circuit diagram of the tube

Rice. 4. Schematic diagram of the base

The handset receiver on the DA1 chip receives an RF signal coming from the base transmitter on transistors VT1 ... VT2, which is modulated by the telephone line voltage. This inclusion of the base transmitter made it possible to achieve the required frequency deviation without an additional modulating amplifier. The processed low-frequency signal is then fed to a dual amplifier on the DA2 chip. Thus, the system is ready to operate in full duplex mode. To operate the transmitter and receiver on one antenna, so that the transmitter signal does not affect its receiver, filter plugs C22, L6 and C15, L3 and selective circuits C14, L3 and C13, L2 are used in the handset and base of the radiotelephone.

When dialing a number from the output of the handset dialer on the DD1 chip, the dialing pulses interrupt the carrier frequency of the handset transmitter on transistors VT1 ... VT2 a number of times corresponding to the dialed digit. This ensures 100% amplitude modulation of the control signal. The same number of times, in the absence of a carrier frequency, the BSN system of the base receiver on the DA1 chip reacts, which locks the key on the DA2 chip, disconnecting the base transmitter on transistors VT1 ... VT2 from the telephone line. Thus, dialing pulses are formed. A similar algorithm is used to reset the telephone line, which is carried out using the “#” key. Redialling a number is done using the “*” key.

Setting up the radiotelephone

Setting up the tube transmitter comes down to tuning circuit L5, C23 to the second harmonic of the quartz resonator, while the carrier frequency must fall in the free section of the 40...48 MHz range. This can be determined by a model receiver having a range of 40...48 MHz. By adjusting R7, the optimal operating mode of the handset transmitter modulation is selected, and by adjusting R5, the optimal operating mode of the transmitter for maximum range is selected. In this case, the current consumed by the handset transmitter should be about 20 mA.

Then the receiver of the base unit is tuned to the frequency of the handset transmitter by tuning L1, and by tuning R1 they achieve reliable occupation of the telephone line and confident dialing. In this case, the line voltage in the occupied state should be 5...10 V.

The base transmitter is configured in the same way when the line is busy using the model receiver. Circuit L7, C22 is tuned to the second harmonic of the quartz resonator, while the carrier frequency of the base transmitter must fall in the free section of the range 40...48 MHz. By adjusting R2, the optimal modulation mode of the base transmitter is selected, and by adjusting R5, the optimal operating mode of the transmitter for maximum range is selected. In this case, the current consumed by the base transmitter should be about 20 mA. Since the radiotelephone operates in duplex mode, there must be a frequency separation of at least 3 MHz between radio channels.

Similarly, tune the receiver to the frequency of the base transmitter by adjusting L1. In the base unit, by adjusting R1, we achieve reliable passage of the low-frequency signal into the telephone line, without drowning out the signal received from the line.

Now a filter plug is connected to the tube and by adjusting L6 it is adjusted to the minimum penetration of the signal from the transmitter to the receiver of the tube. Similarly, connect the filter plug in the base and adjust it by adjusting L3. By adjusting the selective circuits L3 in the handset and L2 in the base of the radiotelephone, better sensitivity of the receiver is achieved. The tube and base antennas are tuned to operating frequencies by adjusting the extension coils L7 and L8. The desired handset volume is selected by adjusting R3. Items marked with (*) are selected during adjustment. At this point, setting up the radiotelephone can be considered complete.

Details and design

It is better to use imported high-quality quartz resonators at frequencies of 20...24 MHz (if they will be excited at the second harmonic). At higher harmonics, quartz should not be excited, since as the harmonic increases, the transmitter power decreases. It is necessary to pay attention to the fact that quartz crystals with nominal values of the fundamental frequency, and not the mechanical harmonic frequency, are suitable for this circuit.

The TDA7021 chip, as a last resort, can be replaced with its domestic analogue - IC K174ХА34. But it should be noted that not all domestic copies can operate in this range. The LM358 microcircuit can be replaced with its domestic analogue - IC K1040UD1 Instead of the K1008VZh1 microcircuit, some dialer microcircuits, such as K1008VZh5, K1008VZh7 and others, are suitable, but with the appropriate switching circuit. The KR1014KT1 microcircuit is suitable with any letter index. The KT368 transistor can be replaced with any RF transistor with a cutoff frequency of at least 300 MHz. The KT315 transistor can be replaced with any low-frequency transistor. KD503 diodes can be replaced with KD522 and others. Any chokes with an inductance of 20 μH can be used. All reels containing! 8...10 turns of PEV brand wire with a diameter of 0.6 mm on a frame with a diameter of 5 mm with a brass trimmer, some of them have a tap from the middle. Extension coils are selected experimentally, since the number of their turns depends on the length of the antennas used. The MKE-84 microphone can be replaced with any electret microphone, only the switching circuit will change. Any telephone capsule with a coil resistance of 16...64 Ohms can be used. The piezo emitter in the base of the radiotelephone can be used from any imported telephone. It is better to use 4.8 V batteries as a power source for the radiotelephone handset. For the base receiver, you can use a 3...5 V power supply or batteries for the same voltage, since the receiver consumes a relatively low current.

The only disadvantages of this design include the absence of a ringing signal on the radiotelephone handset in standby mode and a limited range. To increase the range of this radiotelephone to 5...10 km, it is necessary to increase the sensitivity of the receiving path and the power of the transmitting path of the handset and base. Increasing the sensitivity of the handset and base is achieved by adding RF signal amplifiers, and increasing power is by adding output power amplifiers operating with high efficiency in class “C” mode. To operate the transmitter and receiver on one antenna, so that the transmitter signal does not affect its receiver, a plug filter and selective circuits, as well as limiting diodes, are used in the radiotelephone.

It should be noted that in this version the maximum power of the base transmitter was achieved with limited power of the telephone line. Therefore, when building a more powerful transmitter in the base, it is necessary to power it from a power supply. To do this, optocoupler isolation is used, where the base transmitter is matched with the telephone line. Reception of the ringing signal on the handset is realized using the silent “BSHN” setting of the receiver, and they also use optocoupler isolation from the telephone line. The number of coil turns in the circuit diagram is indicated approximately, since their inductance depends on many factors, so selection of turns cannot be avoided.

Rice. 5. Circuit board tube

Rice. 6. Printed circuit board base

I have assembled several such structures, which showed excellent results during operation. At the same time, reliable communication in urban conditions was up to 300 meters, and the frequency stability of the radiotelephone transmitting path was not inferior to industrial products. Despite the simplicity of the design, I recommend it for repetition by radio amateurs who have at least some experience in the manufacture and configuration of receiving and transmitting devices, as well as knowledge of the operating principle of telephone equipment.

Literature

1. Shumilov A. Simple radiotelephone // Radio amateur. 2001. No. 7.

2. Shumilov A. Returning to what was printed // Radio amateur. 2001. No. 9.

3. Shumilov A. Simple radiotelephone VER 1.0 // Radio amateur. 2002. No. 1.

4. Shumilov A. VHF receiver with extended range // Radio amateur. 2002. No. 3.

5. Shumilov A. Simple radiotelephone Veg 2.0 // Radio amateur. 2002. No. 5.

6. Shumilov A. Returning to what was printed // Radio Amateur. 2002. No. 6.

7. Shumilov A. Simple radiotelephone VER 2.1 // Radio amateur. 2002. No. 9.

8. Shumilov A. Universal radio signaling // Radio amateur. 2003. No. 2.

9. Shumilov A. Stereo receiver with a digital scale // Radio amateur. 2003. No. 5.

10. Shumilov A. Radio pager // Radio amateur. 2003. No. 12.

11. Shumilov A. Duplex radio device // Radio amateur. 2004. No. 2.