Diagram for connecting a voice recorder to a telephone line. Recording telephone conversations. SpRecord telephone conversation recording systems

Attention! The ATL-2U adapter is outdated and discontinued!
As a replacement, use

Adapter ATL-2U is device for connecting up to 2 landline city telephone lines to computer sound card for recording telephone conversations on computer. Recording can be done using computer software into two independent audio recording channels.

Adapter ATL-2U:

• connects to each two-wire telephone line in parallel (for example, through a twin RJ11 splitter), does not require breaking the line wires;
• connects to the linear stereo input of the computer sound card (blue or blue color sound card);
• works with almost any integrated and installed sound cards;
• works with microphone inputs (red connector) of laptops and computers, provided that only one telephone line is connected to the adapter for recording;
• does not require additional external power, has microcurrent consumption from the telephone line;
• does not affect the operation of the telephone, telephone line and telephone exchange, due to the high input impedance;
• has built-in varistor protection against voltage surges in the telephone line caused by natural and man-made reasons;
• has a built-in galvanic isolation to eliminate interference - “current loops” and ensure the safety of people and equipment;
• has built-in electronic switches that disconnect the computer's sound card from sound signals from the telephone line when the handset of the telephone is inactive (lowered), thereby preventing the penetration of extraneous noise and interference from the line to the input of the sound card;
• matches the amplitude and limits the peak level of signals arriving at the linear input of the sound card for its reliable, correct operation;
• works with almost all existing office and city PBXs, provided the adapter is connected to analog ports (analog telephone lines);
• compatible with a variety of software to record sound through a sound card, but we still recommend using it only in conjunction with a specialized one that has a voice-activated recording function (acoustic start) and a system for automatically adjusting the sound recording level.

1. PURPOSE

The ATL-2U adapter is designed for recording telephone conversations on a computer by connecting through it up to two analog subscriber telephone lines to one linear stereo input of one computer sound card in order to ensure coordination, input and through two independent channels.

The ATL-2U adapter provides:

• work with analog telephone lines, including standard city lines (without multiplexing and number pairing devices!), as well as internal and external analog lines of existing mini-PBXs (except for the system telephone line of some types of four-wire PBXs). More detailed information see FAQ: Is it possible to connect the AudioSpy system to a Mini-PBX? .
• correct transmission of outgoing pulse and tone dialing signals from a local telephone number to the inputs of the sound card to ensure support for the caller ID function of outgoing calls when working with AudioSpy software.
• matching the dynamic range of telephone network signal levels with the operating dynamic range of standard Sound Blaster sound cards
• limiting the amplitude of signals arriving at the sound card input to 1V
• galvanic isolation of the telephone line from the computer to prevent interference (from closed 50Hz current circuits) and protect the computer from high potentials and voltage surges in the telephone line
• varistor protection of the adapter at the inputs of telephone lines from induced impulse voltage on cables from atmospheric lightning discharges, as well as man-made sources of pulsed electromagnetic fields
• automatic electronic shutdown of audio paths when there is no connection (the handset is down) to prevent line interference from penetrating the sound card inputs
• automatic electronic switching sound paths when there is a connection (call tone, handset is lifted)
• frequency filtering of input signals to cut off low-frequency and high-frequency interference (AC background, RF multiplex signals, etc.)
• the fact that the device is connected to the telephone line is invisible to telephone subscribers due to the operation of the ATL-2U in low current consumption mode
• parallel connection to the telephone line - does not require breaking telephone wires
• lack of power from a 220V network or batteries due to micro-consumption from the telephone network.

External view of the ATL-2U adapter delivery kit (click on the picture to enlarge).

2. TECHNICAL CHARACTERISTICS

• Maximum number of simultaneously connected telephone lines...2
• Number of connected sound cards...1
• Sound card input used...line stereo
• Transmission coefficient of sound paths...-15 dB
• The voltage limiting the amplitude of pulse signals arriving at the Sound Blaster is no more than...1V
• Threshold line voltage at which audio signals are turned off/on
  paths...20(+/- 3) V
• Maximum current consumption from the line in the absence of communication (the handset of the subscriber device is lowered)...0.4 mA;
• Maximum current consumption from the line in the presence of communication (the handset of the subscriber device is lifted)...0.8 mA;
• Operating frequency range -3dB...250-18000 Hz
• Load resistance (Line-In input of the sound card), not less than...10 kOhm
• Nonlinear distortion coefficient, no more than...1%;
• Overall dimensions (w,h,d), no more than...150 x 30 x 80 mm;
• Weight, no more than...400 g.

Connecting the ATL-2U adapter to the telephone line and to the recording computer

Telephone adapter

To record telephone conversations, devices are used that automatically connect recording devices when the telephone is picked up. One of the diagrams of such an adapter is shown in Fig. below.

The operating principle is as follows: When the handset is not picked up, there is a voltage of about 60 V in the telephone line. Through a divider assembled on resistors R1-R3, it goes to the gate field effect transistor VT1 type KP10ZM and locks it. This leads to the closure of transistor VT2 type KTZ15 and transistor VT3 type KT814. Relay K1 type RES22 is de-energized and its contacts K1.1-K1.4 are open. When the tube is lifted, a voltage of 5-15 V is established in the line, which leads to the opening of transistor VT1 and, consequently, transistors VT2 and VT3. Relay K1 is activated, which, with contacts K1.3 and K1.4, supplies 220 V power to the tape recorder, which is previously turned on for recording, and at the same time, with contacts K1.1 and K1.2, connects the telephone line through capacitors C1 and C2 to the input of the tape recorder. The tape recording of the conversation begins. The SZ capacitor smoothes out ripples and noise induced in the line, which can cause false alarms of the device. When connecting the device to the line, the power polarity must be observed. The device can use any power transformer that reduces the voltage to 12 V and is designed for a load current of more than 0.1 A.

It is well known that many programs for recording telephone conversations have been written for all mobile platforms. These are well-known programs such as rVoix, AudioSP, Auto-call, Psiloc Xelnex - you can use them. But what if you need to record a conversation over a regular landline telephone or wired speech source? This is where this simple device comes to the rescue, which does not require scarce parts or extensive experience for its manufacture.

In TV shows you can often see how the problem of recording telephone conversations is solved using a camera and a phone with speakerphone turned on. Naturally, the recording quality and intelligibility in this case leave much to be desired. Once I saw a prosecutor have a special voice recorder with RJ11 connectors for recording telephone conversations. This is how the idea of ​​creating a telephone line adapter for a regular voice recorder came about.

Device diagram

Adapter circuit for a telephone line for recording conversations before and after alteration

I took the old D-LINK splitter DSL-30CF as a basis. It turned out to have exactly the same circuit as most cheap splitters. On the Internet I managed to find a circuit diagram for a Zyxel splitter, exactly like mine. The diagram shows that the connectors: LINE and ADSL are connected directly to each other, and the PHONE connector is connected through a high-pass filter. From the circuit I removed both transformers and all four capacitors (They will be useful to me for making a “spy” wire tube). I left only the sockets and varistor (let the phone be protected from voltage surges and the ears from loud clicks). I soldered jumper wires into the circuit to make a telephone splitter (by the way, you can use this device exactly like this). In the top cover of the splitter I made two holes for headphone jacks, so that they fit tightly there, and so that they fit into the space between telephone sockets that was freed up after dismantling the high-pass filters.

In the diagram I used electrolytic capacitors rated for 50V. You can take it with great tension. You can also exclude one of the headphone jacks from the circuit. I installed two so that I could control the recording process.

As a voice recorder, I used an old MP3 player from RoverMedia, model: Aria DP300FM, since it has a linear input for recording in one of the selected formats and is equipped with a special connecting cord, which I used. In addition, this player has a great feature: record only when there is a signal. Of course, you can also record on a regular voice recorder or computer via a line input. It happens of blue color. Or if it is missing through the microphone (it can be red). In any case, you should adjust the signal level before starting recording.

If you don't have an adapter cord, you can easily make one from a pair of old headphones by simply connecting the corresponding leads together.

The operating principle of the device is very simple. As you know, telephony uses several components of operating voltage. When the telephone is hung up, the ringing circuit is connected to the line through a capacitor of about one microfarad. There is no direct current flowing through this line, but when a ringing signal is applied to the telephone, greater than 100 volts and about 25 Hz, the capacitor is recharged and current flows through the ringer. When the handset is picked up, the speaking and dialing circuits are connected to the line, creating DC resistance in the line.

This is how the station determines whether the device is ready to dial a number or connect. Since the adapter does not create resistance to direct current, it does not interfere with pulse dialing and does not occupy the line, which means it can be on the line constantly. As can be seen from the adapter diagram, when the voice recorder or headphones are turned off, it has no effect on the telephone line at all (except for varistor protection).

You can connect the adapter using a 15-centimeter cord that is usually supplied with ADSL modems. You can also make it yourself using a crimper from a piece of telephone cable. It should be taken into account that in analog telephony two middle RJ11 pins are used (usually red and green).

Using such a cord, you can connect your phone via an adapter, or plug the adapter into any parallel telephone socket (only after the splitter, otherwise the adapter capacitors will bypass the ADSL through the recorder input circuits). I plugged the adapter into the additional connector on the telephone itself; it is usually connected in parallel with the main one.

The adapter is now constantly included in our phone, since it turned out that it is very convenient to participate in a telephone conversation through the connected headphones. In addition, you can connect computer speakers instead of or together with the voice recorder. Thank you all for your attention. The article was prepared by Zilord.

In general, the topic itself is not new, but a review of amateur radio and professional sites dedicated to communication technology showed that interest in this topic does not wane. Such gadgets are produced by individual commercial companies, but for some reason their products are distributed mainly through online stores, and the prices are quite high. Adapters designed for recording telephone conversations are sold included with digital voice recorders, but they become useless if you are the “lucky” owner of a paired number - the telephone’s polling pulses are not filtered by the standard adapter and are perceived by the voice recorder’s microphone input. As a result, the function of activating recording by a sound signal does not work - the voice recorder is always on, regardless of whether the handset is removed from the device or put down. Meanwhile, making a high-quality adapter that takes into account the realities of the domestic telephone network is not at all difficult. The adapter will help you record the necessary call with important information on a voice recorder (tape recorder, computer).

I tried to “settle down” various circuit solutions that I came across on the Internet and in the literature. Figure 1 shows the conditional classification of adapters by type and, accordingly, by application options with certain recording devices:

The most convenient, of course, is a parallel connection to the telephone line. But, such an implementation imposes certain technical requirements on the circuit and its elements - the adapter is the load of the PBX line. Figure 2.1 shows possible connection points for the adapter parallel to the PBX line.
Inserting an adapter into a break in one of the line wires undoubtedly simplifies the circuit design, but then the telephone line will have to be broken, and the location of the break will have to be “calculated” depending on which section of the line it is necessary to control the telephone sets. Such adapters are more suitable for working with an individual telephone and are usually located near it. Figure 2.2 shows examples of connecting a line wire to a break. To record from all telephones, the line wire is broken at the beginning of the telephone wiring. In the figure, this is a special socket for the adapter, and the adapter must be constantly connected to it. If the adapter is disconnected, then a plug with a jumper is inserted into the socket instead, otherwise the telephone connection stops working in the entire room.
Adapters without galvanic isolation from the telephone line are used with voice recorders that are battery-powered and (or) receiving external power from a conventional transformer source with a stabilizer.
For recording devices powered by pulse source power supply (for example, computers, digital voice recorders with battery charging via a USB connector), adapters with galvanic isolation are required. This, firstly, will ensure safe operation of the device itself, and secondly, it will not affect the telephone line in terms of “leakage to ground”. As you know, the positive pole of the central battery at a telephone exchange is always grounded.
Adapters that do not control power are easily connected to the voice recorder - communication is only via an audio cable. As they say, “Plug and Play” - connect and play. But only voice recorders can work with such adapters for a long time. Only voice recorders have a voice activation function (sound signal). Using conventional cassette tape recorders for long periods of time in standby mode will not work; they do not have a voice control function in recording mode. Therefore, tape recorders with such an adapter can only be used for local recording - turned on at the beginning of a conversation and turned off at the end.
Another thing is the adapters that control the power supply of the recording device. When you lift the handset from the device, power begins to flow to the device that is in recording mode and it is activated. While on-hook, standby mode can continue indefinitely, with the battery or AC power source completely disconnected. Here, by the way, the problem of operating a recording device on a paired PBX line is automatically solved.
Using a telephone line energy adapter to operate is classic version regardless of other types of circuit design. Here, both transformer connection to the line and capacitor connection can be used. But these are the simplest solutions. The functionality of the adapter can be expanded by additional power supply, which can be conveniently used as an external power source for a recording device.
By implementing the types listed above in the required combinations, it is possible to produce an adapter circuit that fully meets the specific application.
There are uninterrupted RTShK kits on sale - a telephone socket with a plug or various types of adapters that allow you to connect imported telephones with a Jack RJ-11 plug to a domestic socket. Such kits or adapters are very convenient to use as an adapter housing:

An example of the simplest adapters included in the break of any linear wire is shown in Figure 3:

A proof-of-concept version of these adapters is shown in the photo:

In the circuit in Figure 3.1, a diode bridge VD1 is connected to the break in the linear wire, the load of which is a fritter built on two germanium diodes connected back-to-back. The voltage drop across VD2 and VD3 is no more than 200...300mV both when there is an incoming call and when the line is seized. A capacitor C2 is connected to the fritter, which produces alternating conversational current. For alternating current, capacitors C2 and C3 are a capacitive divider and form a kind of filter. From capacitor C3, the alternating signal from the line is supplied to the microphone input of the cassette recorder. Capacitor C1 additionally bypasses the input circuit of the adapter. It eliminates noise that occurs on the telephone line when the handset is placed on the machine and reduces the impact of AC call voltage. The operating voltage of the capacitor must be no less than that indicated in the diagram. You can install a line occupation indicator in this circuit if, instead of VD2 and VD3, you turn on the LED with the anode to the plus of VD1. In this case, the constant voltage will be limited to the level of the voltage drop of the type of LED used.
In the circuit in Figure 3.2, two silicon diodes VD1 and VD2 and the primary winding of transformer T1 are included in the line wire gap. The voltage drop across the diodes does not exceed 600...700mV both during an incoming call and when dialing a number, therefore the diodes limit the voltage amplitude of the primary winding T1 to a safe level. From the secondary winding T1, the signal goes to the tuning resistor R1, with the slider of which you can set the required level of the alternating signal at the microphone input of the recorder. Capacitor C2 is a separation capacitor. It is necessary if the microphone input of the recorder is “on duty” in recording mode. constant pressure(usually 0.9...1.5V), which is used to power a connected external electret microphone. Capacitor C1 additionally eliminates interference. Transformer T1 can be used in any type, as small as possible, with a transformation coefficient Ktr = 1...10 and is selected experimentally according to the nominal level of the recorded signal.
Another version of the circuit design of the adapter, connected to the line wire break, is shown in Figure 4. Here, the adapter uses a relay:

Figure 4.1 shows a diagram of the adapter that controls the power supply of the voice recorder. In the initial state, when the handset is hung up, a voltage is applied to the diode bridge VD1, determined by the current that the telephone consumes from the PBX line in the storage mode of the last dialed number, if it is an electronic telephone with push-button dialing. There is no voltage applied to the VD1 bridge if it is a classic SLT with a rotary dialer. The adapter is connected in series with the TA bell circuit. When an incoming call arrives - alternating voltage with an amplitude of 90...120V, the phone begins to ring, while the ringing voltage is rectified by the VD1 bridge. Through the HL1 LED, windings K1 and K2, the circuit is closed to minus VD1. The HL1 LED indicates the presence of a ringing signal on the line. But the current of the telephone ringing circuit, sufficient to ignite HL1, is not enough to create a voltage drop across the resistance of the relay windings so that they work. Therefore, the relays remain in their original state, their contacts K1.1 and K2.1 do not switch, and as a result, the voice recorder is not activated. When the handset is removed from the device, the line is engaged and a current begins to flow through the adapter, sufficient to ignite HL1 and operate the relay. Contacts K1.1 switch, closing the power supply circuit of the recorder, and contacts K2.1 connect the decoupling C3 to the plus of VD1. The voice recorder records the conversation. When the handset is returned to the device, the circuit returns to its original state - power is removed from the recorder by the open contacts K1.1, and decoupling C3 is closed to the common wire by contacts K2.1, i.e. recording stops. Capacitor C1 is a storage capacitor and releases its energy when a number is dialed, ensuring that the relay is kept in the on state. Without it, the relays will switch with the dialing frequency (standard F=10Hz). LED HL1, in addition to serving as an indicator of an incoming call and line occupation, blocks the shunting effect of capacitor C1 on alternating conversational current. Capacitor C2 is anti-interference. Diodes VD2 and VD3 eliminate negative surges of self-induction voltage that occur when the relay is released. Recommendations for using the relay are given in the diagram, but we must not forget that the resistances of the windings K1 and K2 are connected in series with the conversational circuit of the telephone and work as an additional resistance when dialing a number. Therefore, the lower their resistance, the better. Using this scheme, a working copy of the adapter was assembled, which fit in a socket with two RJ-11 connectors:

Contacts K1.1, operating in the power supply circuit of the recorder, can be connected as follows. An insert is made of thin but hard non-conductive material, which is placed between the battery and the contact in the voice recorder body. If this insert is used for one battery, then it is made according to the diameter of the battery and has two contacts on different sides:

If this is an insert for two batteries, then it can be made rectangular:

In both cases, you need to make a small, neat cut with a needle file in the battery compartment lid for the wire going from the insert to the adapter. Then it will turn out quite aesthetically:

In order not to pull the wire out of the battery compartment every time you listen to a recorded fragment, the adapter has an SA1 switch (see Figure 4.1). The closed contacts SA1.1 are included in the audio circuit, and the open contacts SA1.2 are included in the power circuit. Before listening to the recording, SA1 is switched, then the power circuit is closed, and the audio signal circuit, on the contrary, is opened. Now you can control the voice recorder using its standard buttons, and the audio signal will not be sent to the microphone input if there is a need for a telephone conversation.
This adapter can not only control the power supply of the voice recorder:

But, also used without power management, i.e. in activation mode by sound signal:

Figure 4.2 shows a simplified version of such an adapter - without controlling the power supply of the recorder. Both schemes - perfect option for work on a paired PBX line.
Examples of adapters connected parallel to a telephone line are shown in Figure 5:

Adapter, control external power supply voice recorder, shown in Figure 5.1. Here, switch SA1 is installed at the input, connecting the adapter to PBX1 or PBX2. Diode bridge VD1 ensures constant polarity of the supply voltage in the circuit and rectifies AC voltage call. Divider R1-R2 and transistor VT1 – line status sensor “busy”; not busy; dialing a number". Elements R3 and C1 are a delay circuit, and VT2 is a current switch that controls the power supply of the recorder. As can be seen from the diagram, the voice recorder supply voltage is switched “minus”. In the initial state, when the tube is laid, the line is not occupied and a voltage of about 2.0...2.3V is present at the VT1 gate. The transistor is open and the voltage potential on the positive plate of capacitor C1 is practically zero, i.e. C1 is discharged and transistor VT2 is closed. The circuit “minus source GB1-GB2” – “minus external power supply” of the recorder is broken. The current consumption from the line by the adapter circuit in this case is determined by the parallel connection of resistances (R1+R2) and R3, i.e. no more than 40 µA. When the tube is removed, the voltage at the gate VT1 becomes less than the threshold and the transistor closes. Through R3, C1 begins to charge and, when the voltage on it exceeds U3 and the threshold, transistor VT2 will open, closing the negative wire of the external power supply of the recorder with the negative of the source GB1-GB2. The recorder turns on and records the audio signal from the line, released by capacitor C2 through R4. Capacitor C3 eliminates interference and interference. The voltage on capacitor C1 will increase until it becomes equal to the voltage in the busy line (as a rule, U=8...15V and is determined by the subscriber device), therefore, it will not exceed Uз-i max VT2. The diagram shows the voltages measured when removing the handset from a GE brand push-button TA, taking into account the input resistance of the digital multimeter. When dialing a number, pulses with an amplitude of up to 60V occur in the line. At gate VT1, the voltage will reach Uз-threshold and it will open again, instantly discharging C1. Transistor VT2 will close, de-energizing the recorder. During the sequence of serial pulses and in the pauses between them, C1 will not have time to charge, periodically discharging through the low resistance (Rc-and open = no more than 10 Ohm) of the drain-source transition VT1, so VT2 will remain closed and the recorder turned off. After dialing the entire number, the C1 will charge and the recorder will continue recording. When there is an incoming call, the picture is similar to the dialing mode, so the voice recorder also remains turned off. The table shows examples of transistors that were tested as VT2, as well as the measured voltage drop (+Upd*) at the open drain-source junction with “fresh” batteries GB1 and GB2. The use of IRFZ44N turned out to be more preferable - the voltage drop was no more than Upad = 4.0 mV.
The adapter according to this scheme was assembled in an “arbacom” socket with RJ-11 connectors due to its increased size, which made it possible to place a case for two AAA batteries, having previously cut a hole to size in the bottom:

The circuit in Figure 5.2 shows the circuit of a non-power-controlled adapter in which the audio output is closed in standby mode. The node on transistors VT1 and VT2 operates in the same way as in the circuit in Figure 5.1, while the voltage U = 60V of an idle telephone exchange line from the bridge VD1 through R4 is supplied to the zener diode VD4 and is limited at the level Ustab = 8...10V. Capacitor C2 smoothes out ripples. The voltage from the cathode VD4 is supplied to the gate VT3 and opens it. With its open drain-source junction, the transistor connects the left plate of capacitor C3 to the common wire. As a result, a capacitor with a capacitance of C = 330nF + 1mF is connected parallel to the microphone input of the recorder, cutting off interference and shunting the alternating voltage of the incoming call, which, thanks to the divider R5 and Rc-and open VT3, is reduced to a noise level. The current consumption of the adapter is determined by the parallel connection of resistors R1+R2, R3, R5 and the current flowing through R4 and VD4. When the handset is removed from the device, transistor VT2 opens and discharges C2, while the gate VT3 closes to the common wire. Transistor VT3 closes and the alternating signal through R5 and C3 is supplied to the microphone input of the recorder. When dialing a number, transistor VT2 will quickly close, but due to the large value of R4, capacitor C2 will not charge immediately, so VT3 will remain closed for some time. To prevent pulses with an amplitude of up to U = 60V from passing through to the microphone input, a protective silicon diode VD2 is installed, limiting the voltage to a level of no more than 600...700mV. In this case, R5 limits the current through the diode. Despite the large ratings of R5 and C4, the level at the microphone input is sufficient for the normal operation of the recording activation mode with an audio signal. You can increase the signal level by adding diodes in series with VD2.
Figure 5.3 shows a circuit diagram of an adapter with galvanic isolation. The drain circuit of transistor VT2 includes LED HL1, which is an indicator of line occupation. When the tube is removed from the TA, resistor R4 eliminates line shunting by the adapter and limits the current through the LED. The voltage drop across the LED (about 1.5...2.0...3.0V and determined by the type) is used to remove the signal from the line. The alternating conversational current through C2 is supplied to winding 1-2 of transformer T1. From winding 3-4, the signal through separator C3 goes to the microphone input of the recorder. Capacitor C4 is anti-interference and reduces the amplitude of the induced voltage during an incoming call in winding 3-4 at the microphone input to a level at which the voice recording activation system does not recognize the signal. This interference occurs despite the fact that transistor VT2 is closed and cathode HL1, together with pin 2T1, is disconnected from the common wire of the circuit. The type of transformer T1 is not known and it is not clear whether it is unified or not. I found some at work and it’s not clear what they are needed for or what device they are used in. They have small dimensions. The measured resistances of the windings are shown in the diagram, although they are not critical - the voice recorder has a deep ARZ in recording mode.
Based on the circuit in Figure 5.3, a dual-line adapter circuit has been developed. I use this adapter at my work. The thing is that I have two phones connected at my workplace. One is a regular ATS with a serial number, and the second is a direct connection with the head of the department, i.e. The phone works with an operational communications switch. Previously, when telephone calls or meetings were held, you had to press the receiver with your shoulder to your ear and manage to write down all sorts of commands of bosses or technical managers. I got tired of it, so this adapter was made. Now I can talk on the phone calmly, and all information is automatically recorded on the voice recorder.
Diagrams of two-line adapters connected parallel to the telephone line and controlling the external power supply of the voice recorder are shown in Figure 6. Figure 6.1 shows a diagram of a two-line adapter with an additional option, and Figure 6.2 shows a simplified version:

As can be seen from Figure 6.1, the adapter has two channels of telephone interfaces, made according to the same circuits. The channels are connected to each other only by the secondary windings of transformers T1 and T2. This achieves galvanic isolation between telephone lines. The signal in the channels is removed through separating capacitors C3 and C4 from the LEDs HL1 and HL2, which simultaneously serve as telephone line occupancy indicators. In addition, emitting LEDs of transistor optocouplers VQ1.1 and VQ1.2 are installed in the drain circuit of transistors VT3 and VT4. transmitting a signal to the external power control unit. Resistors R7 and R8 limit the current and eliminate shunting of the telephone line when the handset is off-hook. The power control unit contains the DD1 microcircuit - four logical elements with the “AND” function and a hysteresis switching characteristic. As an additional option for a voice marker that marks the time of completion (or start and end) of recording a fragment, a talking clock “TALKING CLOCK” has been added to the node.
The operation of both telephone channels is the same, so I will consider the operation of only one, for example, the first. When the tube is laid, transistor VT3 is closed, so no current flows through the LEDs VQ1.1 and HL1. Resistor R14 sets logic 1 at inputs 1,2DD1.1, so there is logic 0 at output 3DD1.1 Low level voltage is set by resistor R16 at inputs 12,13DD1.2, so output 11DD1.2 is logic 1. Log.1 from output 10DD1.3 through the integrating circuit R17-C13 is supplied to input 6DD1.4. The input of 5DD1.4 is also logic 1, so the output of 4DD1.4 is logic 0. This log.0 closes transistor VT7. Transistor VT6 is securely locked with positive potential on the base from resistor R12, so the supply voltage from source GB1-GB3 is not supplied to the recorder. Logical 1st from output 11DD1.2 transistor VT5 is closed and LED HL3 is turned off.
An incoming call does not trigger any processes in the power management node, so the voice recorder remains turned off.
When you remove the handset from the device, the line is engaged. VT3 opens and current begins to flow through VQ1.1 and HL1. The HL1 LED indicates line occupation, and the phototransistor VQ1.3 opens in the optocoupler. At inputs 1,2 DD1.1 the voltage drops to the log.0 level. Now at inputs 8 and 9 of element DD1.3 there are two logic 1s, and at its output 10DD1.3, respectively, log 0. This log.0 quickly discharges C12 thanks to the VD5 diode and also quickly discharges C13 thanks to the VD6 diode. From output 4DD1.4, log.1 opens VT7, which, through the limiting current R13, connects the VT6 base to the common wire of the circuit. Transistor VT6 opens and power supply to source GB1-GB3 is supplied to the recorder through the emitter-collector junction VT6 and diode VD3. The recorder, previously switched to recording mode, begins to record the signal from the secondary winding T1. The signal from T1 is fed to the microphone input through separator C5.
When the tube is placed on the device, phototransistor VQ1.3 closes and logic 0 appears at the output of 3DD1.1 with a short delay determined by elements R14 and C10. Element DD1.3 inverts this logic 0 and logic 1 appears at the output 10DD1.3, which is supplied through the discharged C12 to the “TALK” input of the clock. This is equivalent to pressing the standard watch button of the same name. The clock reports the time, and a PWM signal with the amplitude of the clock power supply appears at the outputs out1 and out2, i.e. U=3V. At the same time, logic 1 from output 10DD1.3 through R17 will begin to charge C13, so logic 1 at output 4DD1.4 will be held for some time, sufficient to start the clock and the recorder will not turn off even for a short time. Further, after charging C13, the on state of the voice recorder holds the PWM signal from the output out1 of the clock, constantly recharging C11 through VD4 and R15. A voltage with a log.0 level from output 11DD1.2 through R10 opens VT5 and the HL3 LED indicates the process of recording a time message to the recorder. The PWM signal enters the voice recorder through R11 and C9. After the time message ends, logic 0 will appear at output 4DD1.4, closing VT7 and VT6, and power will be removed from the recorder.
If you pick up the handset not to answer an incoming call, but to call yourself and start dialing the number, then the dialing pulses on the line will close VT3, therefore, the power control unit circuit will work as when hanging up the handset. Therefore, the watch will also report the time and the voice recorder will record a voice marker. Thus, when answering an incoming call, the time message will be recorded at the end of the conversation, and when answering an outgoing call with dialing, the time message will be recorded at both the beginning and the end of the conversation.
The voice recorder circuit was placed in a housing from a used musical apartment bell “Door bell” with battery power and corridor lighting:

The watch’s “holders” for the strap were ground off using a file, and a hole for the watch was cut out in the bell body. After which the watch was glued with “second” glue:

Two telephone connectors were placed inside the case and the board was cut to size:

In Figure 6.1, a fragment of the circuit is highlighted in blue. This is a PWM signal amplifier for the BF1 dynamic capsule. When the assembly was completed, the amplifier was added to the circuit. The measured resistance of BF1 is R=140 Ohm (a telephone capsule from a dead cell phone is used), so the sound is not loud. Let him purr. Capacitor C8 allows you to record a voice marker if the adapter is used with a voice recorder without power management. If there is no need to record a voice marker, then C8 does not need to be installed. Diode VD3 reduces the supply voltage to the recommended U=3.6V. At the collector-emitter junction of transistor VT6 with this model of voice recorder and “fresh” batteries, no more than U = 0.33V drops.
In the circuit in Figure 6.2, phototransistors VQ1.3 and VQ1.4 are included in the gate circuit transistor switch KP505A. When the phototransistors are closed, the zero potential on the gate is set by the resistor R=560K. Power switching in the circuit is carried out “minus”.
The topic suggests watching demo videos. Test calls were made to the telephone informant of the city cinema. The first video shows a conversation recorded on a voice recorder, and the second video shows a conversation recorded on a laptop. For testing, I downloaded a simple program for recording from the microphone input from the Internet. Naturally, there are more “advanced” programs, for example, that automatically start recording when there is a signal at the input of the sound card.

RECORDING A TELEPHONE CONVERSATION ON A DICTAPHONE

RECORDING A TELEPHONE CONVERSATION ON A LAPTOP

In various dispatch services, in enterprise offices, and in some everyday situations, it may be necessary to record telephone conversations. Of course, there are now various digital “recorders”, but this is equipment that needs to be purchased specifically. Despite the fact that almost any obsolete and no longer used cassette tape recorder capable of recording an audio signal, at least with mediocre quality, can be used to record telephone conversations.

How to record a telephone conversation

The website shows a diagram of a matching device that provides automatic recording of telephone conversations on a cassette recorder. The circuit connects to the telephone line anywhere and can record conversations from any number of parallel telephone sets. The recording device, as mentioned above, is any working cassette recorder. From this circuit, an audio signal is supplied to it, and the contacts of relay K1 are connected to the open circuit of the power supply circuit of the tape drive motor of the tape recorder.

If the tape recorder circuit has a 9V DC source, this circuit can be powered from it. Otherwise, from any separate current source with a voltage of 912V.
The system operates as follows. You need to connect the system to the telephone line, turn on the tape recorder for recording (turn on its power, press the “record” or “record” button).

Since the power supply to the tape recorder's motor will be turned off, recording will not occur. When you pick up the handset on any of the telephone sets connected to this line, the contacts of relay K1 will close and recording will begin. Important point, if the tape recorder has an auto-stop that does not allow the mechanism to remain stationary for a long time, it must be turned off or dismantled.

Now about the operation of the circuit. When the line is not busy, there is a relatively high DC voltage (usually more than 40V). The stabilization voltage of the zener diode VD7 is much lower (12V), so its reverse resistance decreases and through it and resistor R3 a certain constant voltage is supplied to the base of transistor VT1, at which transistor VT1 opens. In this case, the voltage at the collector VT1 is low and transistor VT2 is closed. No current flows through the relay winding, its contacts are open and no power is supplied to the tape recorder's electric motor.

When you pick up the handset, the line voltage drops to 5-10V, sometimes lower (depending on the telephone). This is lower than the stabilization voltage of the zener diode VD7, so the current through it stops. The voltage at the base of VT1 gradually drops as capacitor C2 discharges, as a result of which transistor VT1 closes. But at the same time, transistor VT2 opens, because the voltage at its base increases. Current flows through the winding of relay K1 and its contacts turn on the power supply to the tape recorder's motor. Recording begins.

After the end of the telephone conversation, the voltage in the line rises again and the power to the LPM electric motor is turned off. The audio signal for supply to the recording path of the tape recorder is generated by the circuit C1R1 VD5VD6. Separating capacitor C1, resistor R1 and diodes VD5 and VD6 form a signal limiter. When setting up, resistance R5 should
choose one at which the recording quality will be optimal.

Relay K1 is an old relay from the remote control of domestic TVs. It can be replaced by any other relay with a 12V winding with a resistance of at least 200 Ohm. Zener diode VD7 is any low-power zener diode with a stabilization voltage of no lower than 12V and no more than 35V. The remaining parts can be replaced with any available analogues.