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A microphone with an amplifier on one board for transmitting a signal over a long distance

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It may be necessary to transmit the signal from the microphone without interference over a long distance, using an unshielded, inexpensive wire.

I designed and manufactured a large number of microphones with an amplifier on one board. These products have proven themselves in work.

On two wire lines of inexpensive wire such as "noodles" and the like, I was able to transmit high-quality sound to a distance of 1 km. In this case, the device was powered by the same wire. Often used by someone - the previously laid wires of telephone lines, alarm lines that were no longer needed.

Circuit diagram.


Description of the circuit.

The supply voltage from the source through the line and the diode overvoltage protection diode VD1 is supplied to the collector of the output transistor VT1, an economical operational amplifier DA1 and an electret microphone.

The R7C3 filter is included in the positive power cable, it is needed for the proper operation of the microphone and operational amplifier. The output transistor, which is a current amplifier, is turned on before the filter. Thus, it is possible to separate the sound signal and the power supplied by the same wires.

The electret microphone is powered as standard through resistor R1. From it, the signal is fed to the non-inverting input of the operational amplifier through an isolation capacitor C1. This capacitor slightly attenuates possible mains interference. The board does not need a metal shielding case. Often put in any suitable plastic box, such as those used in electrics. The voltage from the divider on the resistors R2 R3 equal to half the supply voltage is also supplied here.

The amplifier is covered by negative feedback. R4 R6 C2. It sets the mode for direct and alternating current, gain and frequency response, weakening possible pick-ups of 50 Hz. Resistor R5 sets the micropower operation mode of the operational amplifier for minimal current consumption.

From the output of the microcircuit, an audio signal is supplied to the base of the output transistor.

The circuit can work in different ways.

1 to low impedance headphones
2 per speaker 50 ohms.
3 to the recording device, for this an additional circuit is provided from the resistor R10 and the capacitor C4.

In case 3, the signal transmission range is the longest.

In practice, I compared the characteristics of my product with industrial designs. All of them were inferior.For example, by transmission distance. Caught some microphones with automatic gain control. At the slightest loud sound, the microphone “locked” for a few seconds, this is bad. In the photo next to my microphone and the factory microphone, which I dismantled from the cab of the decommissioned elevator. It is larger in size, the gain is less, the elevator can only be called when you get stuck.


Consumption depending on the line resistance at a supply voltage of 12 volts is indicated in the diagram. The range of transmitted frequencies is sufficient for very high-quality voice transmission. The transmission distance is up to one kilometer. No interference, no interference at the output (often a line was laid next to power cables). In the circuit, various electret microphones of different types and sizes are tested. They all worked, the difference was in sensitivity. It can be adjusted by selecting R1 and R6. In the board shown not a photo, there is a tuning R6.
Photo of the finished board from above

Photo of the finished board below

PCB drawing
A microphone with an amplifier on one board for transmitting a signal over a long distance


Examples of application of this device.
To control the sound environment in the room when the guard is in another room.
For alarm systems based on the sound principle.
For voice announcements in broadcast systems when the amplifier is in another room.

I also made a simplified version of the product, but its characteristics are much worse.
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28 comments
0
Reply To quote A complaint
R555 and Starpom In-in, if you had listened to me before, you would have already become millionaires in copyrighted home-made products)). All the same, the inscription "Imdmyself.com" on paper is necessary.
R555 "I didn’t transmit the twisted pair cable sound signal, but a color video signal, directly up to 50 meters without coordination and noticeable distortions. And with two transformers on ferrite, 200 meters."
Toist at 200 m is it still possible to complete the video a bit? Well, how do you make the phone in two circuits in this circuit. Two microcircuits plus a silent-say switch, then I’m in the know. I was thinking about real time without a switch is possible?
Author 0
Reply To quote A complaint
Ivan_Pokhmelev, I guessed today to read this section of the rules before reading this your comment. And if I had read this section of the rules carefully earlier, I would have 8 homework made by myself. But they paid a fee.
0
Reply To quote A complaint
Quote: R555
But what, just put paper on it, if I draw in the graphics editor, put it in the background, it won’t work?
Of course not. Read the rules, it is not long and not difficult. ;)
Author 0
Reply To quote A complaint
The new Standard, I think, is starting to understand about the tablet. I already sent 2 more home-made products without her, the next, probably, I will be with her. But what, just put paper on it, if I draw in the graphics editor, put it in the background, it won’t work? Did I understand correctly? About the video signal transmission through my microphone amplifier for 1 km, I did not say. It is not for such frequencies. And I can show audio on the basis of this amplifier in both directions, even from one power supply. And without a local effect.
+1
Reply To quote A complaint
R555 and Starpom You have beautiful, valuable home-made products, but you probably still have not figured out how to properly arrange them. In a nutshell, I’ll explain: For AUTHOR'S home-made work, you need to make at least ONE home-made photo on the background of the inscription "Imdmyself.com", plus at least 3 steps in the process of making home-made.It is the inscription "Imdmyself.com" as proof that it is you (and not plagiarism from the Internet) (because it’s difficult to fake, because the inscription is in the context of a photo with corners and shadows, remember how to take a photo of a gas meter, for taking testimony, photo inspector and the counter number is visible to yours or not to your device) they made a homemade work and therefore it can be called AUTHOR'S! The discussion about what is needed In the AUTHOR'S home-made article to lay the background "Imdmyself.com" on the thought that it would cause such a resonance of views))).R555 You have an interesting microphone circuit with an amplifier, it’s a pity that you didn’t correctly design it as an author. Is there a video signal for this circuit for 1 km without wire shielding? And so, what would two-wire telephone communication on that circuit be done?
0
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Quote: R555
But there were devices with trance, but the effect was.
In addition to the transformer, the differential system includes a balanced circuit, which serves to coordinate with the line. If it is not configured, then there will be a signal creep. A differential system can be made without a transformer, on resistors, simply there will be more losses.
Author 0
Reply To quote A complaint
Yes, I remembered about this effect. Most interesting, I collected several so-called telephone operator handsets, there were no transformers there, and there was no local effect. But there were devices with trance, but the effect was. I was advised about Kizluk’s book on telephony. I found it in my library and refreshed some points. A good book, I recommend to everyone who is interested in telephony issues. Cellular communications, of course, replaced the wired, but not quite. Personally, I have a landline phone at home, but it works through optics and a router.
Author 0
Reply To quote A complaint
I want to add that I did not transmit twisted pair cable not just sound, but a color video signal, directly up to 50 meters without coordination and noticeable distortions. And with two transformers on ferrite, 200 meters.
0
Reply To quote A complaint
In telephones, the transformer is not intended for galvanic isolation. He is there the main part of the differential system, which provides a counter-effect.
Author 0
Reply To quote A complaint
Yes, I remember this book, but I did not have it, although now, probably, can be found on the Internet.
+1
Reply To quote A complaint
I made an apparatus for checking phones for a store (selling phones) (autonomous pre-sale verification). When connecting 2 telephones, a relay coil was used as an isolation (load). Oh, and for a long time it was ... Regarding telephony issues, it was then well stated in the book by A. Kizlyuk, "A Handbook on the Design and Repair of Telephone Devices ..." that survived several editions.
Author 0
Reply To quote A complaint
Ivan_Pokhmelev. I thought, remembered a simple telephony scheme. Transformers for all subscribers are in the devices, but the power constant is transmitted somehow via a 2-wire line. Without constant PBX will not respond to the subscriber.
+1
Reply To quote A complaint
Multichannel communication is indispensable without transformers. There they are needed for galvanic isolation, and not for coordination of resistances. Here we are talking about single-channel communications at relatively short distances, up to 1 km. Of course, transformers could also be used here, but for their full use, 4 wires would have been required, and not 2, and the transmitter would become much larger in size and noticeably more expensive.
Guest Vita 0
Reply To quote A complaint
In connection, matching transformers along the line length are used.
+1
Reply To quote A complaint
What nafig special agreement for spare parts? It is better to transmit a signal over long distances over a twisted pair cable (any, not just computer, its wave impedance is on the order of 100 ... 150 Ohms, for a ribbon "noodle" of TRP - about 250-300 Ohms. The author's resistance on the receiver side is of this order If you really need it, you can pick it up, but most likely it will not be required.
Guest Vita 0
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Ohm's law is probably known, but the theory of long lines for an alternating signal is far from all (matching, reflection, attenuation).
Author +1
Reply To quote A complaint
As the author of this scheme, I will show the transmission of audio; do not wake the KGB of the USSR in me.
Author +2
Reply To quote A complaint
I answer your advice. If I untie the opamp from the output transistor, the circuit will not work. You yourself try to make such a sound transmission at a distance as you suggest. You will need to install power supplies and amplifiers at both ends. About the fact that the signal at the end of the line will decay and need to be amplified, study Ohm's law first. The current in the circuit is the same throughout, and my circuit just works on current. Think about why I didn’t put any KT315 at the output. Who will hear this himself, what is the excitation of the circuit? In the description, I explain in detail the purpose of the power filter C3 R7. Here it is just against these phenomena and set. Moreover, based on my scheme, you can make a two-way system with power on one side. You do not deny that you can talk on a regular landline telephone at the same time, but you don’t have a power supply at home, but it is on the telephone exchange and there are only two wires.
+1
Reply To quote A complaint
Quote: Guest Alexander
The output transistor untie galvanically from the opamp.
What for? In order to decouple precisely galvanically, and not just over a change, you will have to install an additional pulse converter, and this is also the size and interference. And most importantly - why?
Quote: Guest Alexander
The oncoming channel will give strong leads on a long wire line, the subscriber will listen to himself. The appearance of self-excitation is possible.
What is the oncoming channel? Where will the return signal come from? You most likely did not understand anything. ((This is not a telephone line, but a one-way wiretapping.
Guest Alexander 0
Reply To quote A complaint
The output transistor untie galvanically from the opamp. Further. When working on long lines, losses in the line will lead to the need to amplify the signal received from the line at the end of the line. The oncoming channel will give strong leads on a long wire line, the subscriber will listen to himself. The appearance of self-excitation is possible.
Guest Alexander 0
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Thank you worthy and competently made a bookmark. For myself
Guest Alexander 0
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Thank you for the work done very competently and with dignity. made a bookmark for himself.
Author 0
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Of course there is. And a greater distance. I am going to publish. Let's call it that. Highly sensitive microphone for recording sounds of wildlife, birds, for example.
Guest Vladimir 0
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Good day. Dear, are there any high-sensitivity microphone circuits in order to listen to speech at a distance of, for example, 8-10 meters? Like a bug.
+1
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R555
Why this modest stand attracted lightning so much - a mystery!
Out of my ear I heard that Ilya the prophet commands lightning, and he has his old accounts with the Soviet power, old accounts, no statute of limitations! aggressive
Author 0
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Guest Shurik 0
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Somehow I collected it for a long time (it seems on UT1, round with 8 conclusions). Heartbeat could be heard.
Power supply 4 batteries + and - 3V. Now it is lazy, the Chinese are already doing everything for us - I ordered various little things with Ali. Convenient - factory assembly, miniature size.
0
Reply To quote A complaint
A properly designed product, the OS is very correctly selected: at the same time, low consumption and the performance of the low-pass filter function. For use on long lines, it would be useful to add two-sided powerful zener diodes or suppressors on both sides.

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