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This circuit is a simple level indicator based on the popular and inexpensive LM3916 chip. The device is perfect for a mixer, amplifier or. It allows you to visually control the level of the audio signal, thanks to which we can avoid overloads and the distortions associated with them.
circuit diagram
Wiring diagram for the LM3916 chip A linear AC voltage signal rectifier operates at the input; it is based on the TL081 operational amplifier, which allows maintaining high accuracy even with input signals of the order of several tens of millivolts. The design of the board allows you to cut it into 2 parts and solder at an angle of 90 degrees. This will make it easy to make an indicator for mounting on the front panel, and for two channels at once - stereo.
About the functions of radio elements
Resistor R4 (2.2 k) limits the current of the LED, and R5 (4.7 k) acts as an "artificial mass" for the operational amplifier U2 (TL081). The input impedance of the system is determined by the value of R1 (470k). Elements R1 (470k), R2 (470k), R3 (10k), C4, D11 (1N4007) and D12 (1N4007) are the piping of the op-amp amplifier U2 (TL081), together they form a rectifier. The circuit must be powered with 9-25 V. The average current consumption is 10 mA at 12 V.
Assembling and setting up the LED indicator
PCB 3916 We assemble the indicator on a printed circuit board. Installation should begin with the installation of one jumper. In the future, you should install the elements R2 and R3, lying under U1 and R1, located under U2. The order of soldering the remaining elements is arbitrary, but it is better to solder the panels for the microcircuits first, since it will be harder later due to the very large compaction of the radio elements. If you want to make a stereo version of the indicator, you can cut the board in the place between U1 and LED, soldering both parts at a right angle. This will allow you to place 2 level indicator boards close to each other (as in the photo).
Homemade LED indicator of audio signal PCB files
The drawing of the board and the location of the parts on it can be downloaded in this
Output level indicator
Today, as an indicator of the output signal level for various sound-reproducing equipment, whole electronic devices, which display not only the signal level, but also another useful information. But earlier, dial indicators were used for this, which were a microammeter of the type M476 or M4762. Although I will make a reservation: today, some developers also use dial gauges, although they look much more interesting and differ not only in illumination, but also in design. Getting an old dial indicator now might be a problem. But I had a couple of M4762s from an old Soviet amplifier, and I decided to use them.
On Fig.1 the diagram for one channel is shown. For stereo, we need to assemble two such devices. The signal level indicator is assembled on one transistor T1, any of the series KT315. To increase the sensitivity, a voltage doubling circuit was used on diodes D1 and D2 from the D9 series. The device does not contain scarce radio components, so you can use any that are similar in parameters.
Setting the indicator reading corresponding to the nominal level is carried out by a tuning resistor R2. The integration time of the indicator is 150-350 ms, and the time of the reverse movement of the arrow, determined by the discharge time of the capacitor C5, is 0.5-1.5 s. Capacitor C4 is one for two devices. It is used to smooth out ripples when turned on. In principle, this capacitor can be abandoned.
The device for two audio channels is assembled on a printed circuit board with dimensions of 100X43 mm (See Fig.2). Indicators are mounted here. For easy access to the construction resistors, holes are drilled in the board (not shown in the figure) so that a small screwdriver can pass through to adjust the nominal signal level. However, only this is the setting of this device. You may need to choose the resistor R1 depending on the strength of the output signal of your device. Because on the other side of the board there are pointer indicators, the elements Cl, R1 had to be mounted from the side of the printed conductors. These parts are best taken as small as possible, for example, unpackaged.
It is necessary to determine the signal level on indicator LEDs to solve several problems (current and voltage indicators, phase change), but most often such a scheme is used specifically to display the sound level.
In modern electronics, indicator LEDs have partly given way to LCD and LED matrix devices. But this type of circuit 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 microcircuits 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 execution of the case in advance, so that later it does not come as a surprise.
The LM3914 has a linear scale that can also be used to measure voltage, while 15 and 16 have a logarithmic scale, but the pinout of the microcircuits is no different.
At the same time, LEDs can be any, imported or domestic, the main thing is that they are suitable for the task. For example, you can use the simplest AL307 diodes, but more complex ones can also be used.
Calculation of the indicator scheme
The compilation of this device does not require any special skills. The calculation of current and voltage indicators can be made in any program, like a drawing.
One of the "legs" (9) of the microcircuit is connected to the positive input of the voltage supply. This way the LEDs will be controlled as a single column. In order to be able to independently adjust the modes when changing the phase, the circuit must include a switch, but it can safely 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 7 and 8 "legs"
For a current of 1 mA R \u003d 12.5 / 0.001 A \u003d 12.5 kOhm.
And for a current of 20mA R \u003d 625 Ohm.
The introduction of a tuning resistor will make it possible to adjust the brightness of the glow, in the absence of such a need, you can put the usual one. The ratings for them will be 10 kOhm and 1 kOhm, respectively.
The final scheme of the LED level indicator will look something like this.
It's perfect for a mono signal, but for stereo, you'll have to add another one to the second channel. They can be combined through a regular network cable, taking into account the phase. An excellent option is to make two identical schemes made in different colors to show 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 microfarad, provided that R4=100 kOhm. The value of R2 can be selected from the range of 47-100 kOhm.
This circuit uses a KT 315 transistor, but it can be replaced by any other with suitable parameters (signal phase, current, lead-to voltage, p-n junction).
Tip: All the necessary elements can be purchased at the radio market or in a store, it is worth considering that the LM3915-16 chips are somewhat more expensive than the LM3914. A less expensive option is to solder components from existing boards.
The end result is something like this:
Assembling a signal strength indicator on your own is a completely solvable task. The main thing is to find what the circuit will be made of, and after that, take a little time to check and debug the device.
Once a friend in the car saw LEDs flashing to the beat of the music. I was tempted to do the same for myself. To begin with, I will decorate the speakers in the computer, and then I will solder the car as well. A friend did not know how and what stands there and blinks. I had to look for something on the internet. One person was very helpful in finding and creating a simple electrical circuit. There are only 3 parts in the circuit, which can be purchased almost everywhere: an LED, a tuned resistor, a diode. The very principled circuit diagram as follows:The level indicator turns out to be very easy to assemble. Even a person with trembling and inexperienced hands can assemble it :) Put a resistor from about 1 to 22 kilo-ohms - this will be enough. The diode put KD226. This rectifier diode is any that can withstand the entire load, of course with some margin. Diodes VD3-VD6 are silicon, with a direct voltage drop of 0.7 ... 1 V and a permissible current of at least 300 mA.
A slightly more complicated circuit is able to 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 it goes to the indication, the less it will reach the speaker, therefore, if you go too far with the number of levels, dips in sound may appear.
In general, it turned out to be a very simple and interesting design of the LED sound indicator. Instead of dim darkness, lighting effects appeared in the room.
So far I have glued it to the subwoofer case, I will continue to think where to attach it. Video of work:
The number of LEDs on the strip affects the brightness, so if you have a powerful enough UMZCH, you can connect a long multi-colored LED strip. Article author: Maxim Shaikov
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