How to make an LED beep indicator from what you have in the house? LED signal level indicator Do-it-yourself LED audio level indicator diagram

Determining the signal level on indicator LEDs is necessary to solve several problems (current and voltage indicators, phase changes), but most often such a circuit is used specifically to display the sound level.

In modern electronics, indicator LEDs have partly given way to devices based on LCDs and LED matrices. But a circuit of this type not only clearly shows the signal level, it is also easy to implement and quite visual.

What to assemble an LED level indicator from?

Analog-to-digital converters (ADC) LM3914-16 can be taken as a basis. These chips are capable of driving at least 10 diodes, and with the addition of new chips, the number of light bulbs can increase almost indefinitely. The indicator can have any color, and it is better to think about the design of the case in advance so that it does not become a surprise later.

LM3914 has a linear scale, which can also be used to measure voltage, and 15 and 16 have a logarithmic scale, but the pinout of the microcircuits is no different.

In this case, LEDs can be of any kind, imported or domestic, the main thing is that they are suitable for the task at hand. For example, you can use the simplest AL307 diodes, but you can also use more complex ones.

Calculation of the indicator scheme

Composing this device does not require any special skills. Calculation of current and voltage indicators can be done in any program, like a drawing.

One of the “legs” (9) of the microcircuit is connected to the positive voltage input. This way the LEDs will be controlled as a single column. In order to be able to independently regulate modes when changing phases, the circuit must include a switch, but it can easily do without it if this option is not needed.
The current passing through the LEDs for a given voltage and phase can be calculated as follows:

R – resistance on legs 7 and 8

For a current of 1 mA R=12.5 / 0.001 A = 12.5 kOhm.

And for a current of 20mA R=625 Ohm.

The introduction of a trimming resistor will make it possible to adjust the brightness of the glow; if there is no such need, you can install a regular one. The ratings for them will be 10 kOhm and 1 kOhm, respectively.

The final circuit of the LED level indicator will look something like this.

It is ideal for a mono signal, but for stereo you will have to create another one for the second channel. They can be connected via a regular network cable, taking into account the phase. An excellent option is to make two identical diagrams, made in different colors to demonstrate the level of each channel. Devices can also change their color range, but this implementation will be somewhat more complicated.

The value of C3 can be equal to 1 µF, provided that R4 = 100 kOhm. The R2 rating can be selected from the range of 47-100 kOhm.

This circuit uses a KT 315 transistor, but it can be replaced with any other one with suitable parameters (signal phase, current, voltage phase, p-n junction).

Tip: All the necessary elements can be purchased at the radio market or in a store; it is worth considering that LM3915-16 chips are slightly more expensive than LM3914. A less expensive option is to desolder components from existing boards.

The end result will be something like this:

Assembling a signal level indicator on your own is a completely solvable task. The main thing is to find what the circuit will be made of, and then spend a little time checking and debugging the device.

The level indicator is very easy to assemble. Even a person with trembling and inexperienced hands can assemble it :) Set the resistor from about 1 to 22 kilo-ohms - this will be enough. The diode was installed KD226. This rectifier diode is any that can withstand the entire load, of course with some margin. Diodes VD3-VD6 are silicon, with a forward voltage drop of 0.7...1 V and a permissible current of at least 300 mA.

A slightly complicated diagram can show five different signal levels, but they can be reduced, for example to two, or increased.

However, when increasing, it should be remembered that by increasing their number, the power consumption of the entire indicator also increases, and the more spent on the display, the less will reach the column, therefore, if you go too far with the number of levels, dips in the sound may appear.

In general, the result is a very simple and interesting design of the LED sound indicator. Instead of dim darkness, lighting effects appeared in the room.

For now I have glued it to the subwoofer body, I will continue to think about where to attach it. Video of work:

The number of LEDs in the strip affects the brightness, so if you have a powerful enough UMZCH, you can connect a long multi-colored LED strip. Author of the article: Maxim Shaikov

Discuss the article THE SIMPLE LED SOUND INDICATOR

An LED signal level indicator simulating a dial indicator is not a new idea, and it would seem that what new can be invented here? Well, in this regard, I did not invent anything.. I even find it difficult to indicate the original source. The goal is different: to make a simple circuit using available elements. The circuit doesn't even include the ubiquitous microcontrollers. Moreover, it’s not easy to solder the board, but to make a complete structure that can be installed in an amplifier without damaging the appearance. And also, based on this circuit, make your own version of the indicator, taking into account your skills in electronics, or, for example, color music. For this purpose, the indicator is made on two boards: an LED control board and an indication board. In this article, I propose 3 indicator options, let’s call them “arrow”, “6E1P lamp” and “arc”. There are also 2 options for scale illumination (A and B). And all this can be done on 5mm, 3mm or SMD 0805 LEDs. Like any other, this circuit has its advantages and disadvantages. Advantage: cheap element base, with high interchangeability, tolerances, relatively simple circuit. Display options, as they say, for every taste. Disadvantages: selection of many elements, otherwise you would have to stick to one type of LEDs. Small dynamic range, i.e. on a powerful amplifier at low volume the indicator will be “silent”. Visual bifurcation of the “arrow”, which is caused by smooth switching of the LM3915 comparators in the “dot” mode. Eliminating this phenomenon is possible, but requires more complexity in the circuit. High density and thin thickness of tracks on the board. The solution is to buy ready-made boards, but I did it myself using photoresist.

The scheme works as follows. The input signal is supplied to VT1. The input signal level is controlled by R1. After amplification and rectification, the input signal is fed to the input of LM3915. LEDs (1 line) are directly connected to the MS outputs. Through transistor switches on VT2-VT11 there are additional 6 lines of LEDs. Transistor switches are used because The thermal resistance of the MS package is 55 °C/W, which allows a maximum power of 1365 mW at an ambient temperature of 25 °C. However, we won’t delve into the boring world of numbers, I’ll just say that no more than 2 LEDs can be connected to each output of the LM3915. Otherwise the MS will overheat. The S1 button switches between the “column” and “dot” display modes. Button S2 turns on additional lines of LEDs, which makes it possible to implement 2 more operating modes of the indicator. As can be seen from the diagram, many elements (R and C) need to be selected. This can be attributed to the scheme's disadvantage and advantage. The selection allows you to use any LEDs without being tied to Vsupply. 12V and adjust the brightness of the indicator LEDs and backlight to your taste. R6 ensures that the “arrow” glows at “zero” in the absence of an input signal. As a rule, selecting R6 is not required when powering the circuit with 12V. If the “arrow” at “zero” is not needed, then we do not install R6. By selecting R7, we set the required brightness of the LEDs connected directly to LM3915 according to the scheme HL7, 14, 21, 26, 35, 42, 49, 56, 63, 70. The smaller R7, the greater the current through the LEDs, the minimum permissible value of R7 is 20 kOhm . Resistor R8 adjusts the brightness of the backlight LEDs. R8 power is at least 1W. Using resistors R9-R18 we adjust the brightness of the remaining LEDs. Approximately 10 kOhm for LEDs with a luminous intensity of 1000 mcd, 1 kOhm for LEDs with a luminous intensity of 200-300 mcd. Capacitor C3 can be used to regulate the inertia of the “arrow”. The device is powered from a stabilized voltage source of 12V with a current of 0.2-0.3A for the mono version. The supply voltage can be increased to 18V.

External design and differences between indicator options. External design is described in the video report. I will add that when selecting the current of the LEDs, you need to achieve a balanced glow of the indicator and backlight. Then the indicator will look beautiful. The illumination of option “A” looks more beautiful than “B”, but is more difficult to manufacture. Find the stencil for the indicator in the LAY file with the board. There is no need to “mirror” boards and stencils when printing. Mount the indicator in the amplifier in any convenient way, behind the front panel window. Do not place near very hot elements. You can slightly tint the front panel glass to hide possible minor defects in the external design. The indicator input is connected in parallel to the output of the volume control or the input of the final amplifier. The setting consists of setting the tuning resistor R1 of the “arrow” of the indicator to +3db at the rated power of the amplifier.

Please note that the sizes of the indicator boards are different and the size of the board is significantly larger than the working window of the indicator. On the “Arc” indicator, the number of yellow and red LEDs used is 26 pcs. for stereo option. This is not reflected in the diagram, but assembly and adjustment are no different. Also, the backlight in various versions uses from 3 to 10 LEDs (see LAY). This is also not reflected in the diagram to avoid confusion.

List of radioelements

The basis of the design is two microassemblies of type AN6884 (KA2284) - this is a ready-made LED signal level indicator used to indicate various values ​​of an alternating signal, to which it remains to connect a few components of the harness and the LEDs themselves. The diagram of such a device is precisely shown in the figure below.

You can see photographs of the assembled and soldered printed circuit board in the figure below, and you can take its drawing made in the Sprint Layout program from the green link above.

The basis of the operational amplifier design is LM324. This circuit uses two quadraphonic operational amplifiers to generate eight slave audio frequency channels.

Another interesting variant of a circuit consisting of 10 LM324 microcircuits and 40 LEDs. If you assemble two identical structures, you can use them in stereo mode. Supply voltage 12 V, current consumption 2.5A

The range of the sound level indicator (ULF power) should be in the range from 0.5 to 50 W. A special feature of the device is that it does not require an external power supply; it receives its volts from the incoming audio signal.

The basis of the circuit is the LM339 chip, which is a quad comparator. The voltage going to the indicator input is doubled using diodes VD1 and VD2 and capacitors C1 and C2, then it goes to the 78L05 stabilizer used to power the LM339 op-amp and to the inverse inputs of the comparators through a voltage divider on resistors R6 and R7. Using tuning resistances R2-R5, each comparator is adjusted to operate at any required level. When the comparator is triggered, the corresponding LED lights up.

Basic device parameters

Circuit supply voltage: 10-18 V
Input voltage at pins 3,16,17, max 6.2 V
U input 50-500 mV

With resistance R6 we adjust the brightness of the LEDs. Using resistor R8 we adjust the lighting level of the first LED. R10 - too, only for the last LED. The integrating chain R4, C3 sets the delay time for turning off the LEDs.

The basis of the simple design is the AN6884 chip, which is an almost ready-made signal level indicator. You can also use a transistor version of the device, but you will need many transistors and the effect will be an order of magnitude worse, and the sensitivity will be generally lower.

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