DIY LED audio signal level indicator on LM3915. Level indicators

1. Indicator board (replaceable).

2. Left channel board.

3. Right channel board.

Indication levels:

Calibration was carried out using a millivoltmeter separately by channel and then as a comparison of the two together. Structurally, the microcircuits are located in panels for ease of replacement, for example, for a logarithmic indicator on the LM3915.

It is based on 10 comparators, the inverse inputs of which are supplied with an input signal through a buffer op-amp, and the direct inputs are connected to the taps of a resistive voltage divider. The outputs of the comparators are generators of incoming current, which allows you to connect LEDs without limiting resistors. Indication can be made either by one LED (dot mode), or by a line of luminous LEDs, the height of which is proportional to the level input signal("column" mode). The input signal Uin is supplied to pin 5, and the voltages that determine the range of displayed levels are supplied to pins 4 (lower level Un) and 6 (upper level Uv).

Table of operating parameters of the LM3914 chip

The current consumption with all LED segments of both channels on is about 1.3A with a 5V power supply. The boards do not use an input signal amplifier, but its sensitivity is such that the lower limit (first segment) can be ignited with less than 20 mV of an alternating signal.

The double channel level has a size of 157x32 mm. Each channel board is separate (left and right) and has a size of 157x24 mm. When assembled, the structure has dimensions: 157x32x45 mm.

To set the correct linearity of the scale, you must select the limits of the lower and upper levels for each chip. In principle, it is possible, if desired, to stretch the scale of each channel several times with a given circuit design.

When making my amplifier, I firmly decided to make 8-10 cells LED indicator output power per channel (4 channels). There are a lot of schemes of such indicators, you just need to choose according to your parameters. On at the moment The choice of chips on which you can assemble an ULF output power indicator is very large, for example: KA2283, LB1412, LM3915, etc. What could be simpler than buying such a chip and assembling an indicator circuit) At one time I took a slightly different path...

Preface

To make output power indicators for my ULF, I chose a transistor circuit. You may ask: why not on microcircuits? - I will try to explain the pros and cons.

One of the advantages is that by assembling on transistors, you can debug the indicator circuit with maximum flexibility to the parameters you need, set the desired display range and smoothness of response as you like, the number of indication cells - at least a hundred, as long as you have enough patience to adjust them.

You can also use any supply voltage (within reason), it is very difficult to burn such a circuit, and if one cell malfunctions, you can quickly fix everything. Of the minuses, I would like to note that you will have to spend a lot of time adjusting this circuit to your tastes. Whether to do it on a microcircuit or transistors is up to you, based on your capabilities and needs.

We assemble output power indicators using the most common and cheap KT315 transistors. I think every radio amateur has come across these miniature colored radio components at least once in his life; many have them lying around in packs of several hundred and idle.

Rice. 1. Transistors KT315, KT361

The scale of my ULF will be logarithmic, based on the fact that the maximum output power will be about 100 watts. If you make a linear one, then at 5 Watts nothing will even glow, or you will have to make a scale of 100 cells. For powerful ULF It is necessary that there be a logarithmic relationship between the output power of the amplifier and the number of luminous cells.

Schematic diagram

The scheme is outrageously simple and consists of identical cells, each of which is configured to indicate the desired voltage level at the ULF output. Here is a diagram for 5 indication cells:

Rice. 2. Circuit diagram of the ULF output power indicator using KT315 transistors and LEDs

Above is a circuit for 5 display cells; by cloning the cells you can get a circuit for 10 cells, which is exactly what I assembled for my ULF:

Rice. 3. Diagram of the ULF output power indicator for 10 cells (click to enlarge)

The ratings of the parts in this circuit are designed for a supply voltage of about 12 Volts, not counting the Rx resistors - which need to be selected.

I’ll tell you how the circuit works, everything is very simple: the signal from the output of the low-frequency amplifier goes to resistor Rin, after which we cut off half a wave with diode D6 and then constant voltage applied to the input of each cell. The indication cell is a threshold key device that lights up the LED when a certain level at the input is reached.

Capacitor C1 is needed so that, even with a very large signal amplitude, the smooth switching off of the cells is maintained, and capacitor C2 implements a delay in the lighting of the last LED for a certain fraction of a second to show what has been achieved maximum level signal - peak. The first LED indicates the beginning of the scale and is therefore constantly lit.

Parts and installation

Now about the radio components: select capacitors C1 and C2 to your liking, I took each 22MkF at 63V (I don’t recommend taking it for a lower voltage for ULF with an output of 100W), resistors are all MLT-0.25 or 0.125. All transistors are KT315, preferably with the letter B. LEDs are any that you can get.

Rice. 4. PCB ULF output power indicator for 10 cells (click to enlarge)

Rice. 5. Location of components on the printed circuit board of the ULF output power indicator

I didn’t mark all the components on the printed circuit board because the cells are identical and you can figure out what to solder and where without much effort.

As a result of my labors, four miniature scarves were obtained:

Rice. 6. Ready-made 4 indication channels for ULF with a power of 100 Watts per channel.

Settings

First, let's adjust the brightness of the LEDs. We determine what resistor resistance we need to achieve the desired brightness of the LEDs. We connect a 1-6 kOhm variable resistor in series to the LED and supply this power circuit with the voltage from which the entire circuit will be powered, for me - 12V.

We twist the variable and achieve a confident and beautiful glow. We turn off everything and measure the resistance of the variable with a tester, here are the values ​​for R19, R2, R4, R6, R8... This method is experimental, you can also look in the reference book for the maximum forward current of the LED and calculate the resistance using Ohm's law.

The longest and most important stage of setup is setting the indication thresholds for each cell! We will configure each cell by selecting the Rx resistance for it. Since I will have 4 such circuits of 10 cells, we will first debug this diagram for one channel, and others based on it will be very easy to configure, using the latter as a standard.

Instead of Rx in the first cell, we put a variable resistor of 68-33k in place and connect the structure to an amplifier (preferably to some stationary, factory one with its own scale), apply voltage to the circuit and turn on the music so that it can be heard, but at a low volume. Using a variable resistor, we achieve a beautiful wink of the LED, after that we turn off the power to the circuit and measure the resistance of the variable, solder a constant resistor Rx into the first cell instead.

Now we go to the last cell and do the same thing only by driving the amplifier to the maximum limit.

Attention!!! If you have very “friendly” neighbors, then you can not use speaker systems, but get by with a connected one instead speaker system a 4-8 Ohm resistor, although the pleasure from setting it up will not be the same))

Using a variable resistor, we achieve a confident glow of the LED in the last cell. All other cells, except the first and last (we have already configured them), you configure as you like, by eye, while marking the power value for each cell on the amplifier indicator. Setting up and calibrating the scale is up to you)

Having debugged the circuit for one channel (10 cells) and soldered the second one, you will also have to select resistors, since each transistor has its own gain. But you don’t need any amplifier anymore and the neighbors will get a small timeout - we simply solder the inputs of two circuits and supply voltage there, for example from a power supply, and select the Rx resistances to achieve symmetry in the glow of the indicator cells.

Conclusion

That's all I wanted to tell you about making ULF output power indicators using LEDs and cheap KT315 transistors. Write your opinions and notes in the comments...

UPD: Yuri Glushnev sent his printed circuit board in SprintLayout format - Download.

About a year ago I got the idea to assemble a 12-220 volt voltage converter. A transformer was needed for implementation. The search led to the garage, where the Solntsev amplifier, which I had assembled about 20 years ago, was found. Simply removing the transformer and thus destroying the amplifier did not raise the hand. The idea was born to revive him. In the process of revitalizing the amplifier, many things have changed. Including power output indicator. The circuit of the previous indicator was cumbersome, assembled on K155LA3, etc. Even the Internet didn’t help find her. But another very simple, but no less effective output power indicator circuit was found.

LED indicator circuit

This scheme is quite well described on the Internet. Here I will only briefly tell (retell) about her work. The output power indicator is assembled on the LM3915 chip. Ten LEDs are connected to the powerful outputs of the microcircuit comparators. The output current of the comparators is stabilized, so there is no need for quenching resistors. The supply voltage of the microcircuit can be within 6...20 V. The indicator responds to instantaneous values sound voltage. The microcircuit's divider is designed so that each subsequent LED turns on when the input signal voltage increases v2 times (by 3 dB), which is convenient for controlling the power of the UMZCH.

The signal is taken directly from the load - acoustic UMZCH systems- through the divider R*/10k. The range of powers indicated in the diagram 0.2-0.4-0.8-1.6-3-6-12-25-50-100 W corresponds to reality if the resistor resistance R* = 5.6 kOhm for Rн = 2 Ohm, R*= 10 kOhm for Rn=4 Ohm, R*= 18 kOhm for Rn=8 Ohm and R*=30 kOhm for Rn=16 Ohm. LM3915 makes it possible to easily change display modes. It is enough just to apply voltage to pin 9 of the LM3915 IC, and it will switch from one indication mode to another. Contacts 1 and 2 are used for this. If they are connected, the IC will switch to the “Luminous Column” indication mode; if left free, it will go to “Running Dot”. If the indicator will be used with a UMZCH with a different maximum output power, then you only need to select the resistance of the resistor R* so that the LED connected to pin 10 of the IC lights up at maximum power UMZCH.

As you can see, the circuit is simple and does not require complex setup. Due to the wide range of supply voltages, I used one pulse arm for its operation. bipolar block UMZCH power supply+15 volts. At the signal input, instead of selecting individual resistors R*, I installed variable resistance with a nominal value of 20 kOhm, which made the indicator universal for acoustics of different impedances.

To change the display modes, I provided for installing a jumper or a latching button. In the final I closed it with a jumper.

Many people remember well how at the dawn of the 80s, tape decks (Japanese) had recording level indicators with peak displays. Having such an indicator at your disposal was the dream of many radio amateurs and music lovers, but assembling it yourself at that time was simply not realistic.
With the advent of microcontrollers, circuitry has changed dramatically, and now the peak indicator circuit does not look more complicated than the circuit a simple transistor radio from the 80s.
We present to your attention a peak signal level indicator on the PIC16F88 microcontroller, mono, LEDs or LEDs are used as indicators LED matrices. The inputs of the left and right channels are combined in it. Or for the second channel it is necessary to make another similar indicator. The number of LEDs in the indicator (matrix) is 40 pcs. An indicator would look good, for example, on such matrices (10 LEDs each).

The indicator can also work in linear mode, with and without peak indication, also in running dot mode with and without peak indication. The peak indication itself operates in two modes - normal and falling. Normal - these peaks burn for 0.5 seconds and go out, falling - these peaks burn for 0.5 seconds and fall down (if the signal level is currently lower than the level that was 0.5 seconds ago).
The indicator diagram is shown below. The LEDs are used at a current of 3 mA, if you install more powerful LEDs at a current of 20 mA, then resistors R1-R8 must be replaced with resistors of 22-33 Ohms. R11-R14 are set depending on the required operating mode of the indicator. To quickly switch modes, you can install switched jumpers (“jumpers”) at the points of their connection with the common wire.

Processor configuration (installation of fuses, fuses)

CP:OFF, CCP1:RB0, DEBUG:OFF, WRT_PROTECT:OFF, CPD:OFF, LVP:OFF, BODEN:ON, MCLR:OFF, PWRTE:OFF, WDT:ON, OSC:INTRC_IO, IESO:OFF, FCMEN: OFF.

id: 1564
yes: 0

770.84 rub.

Project-002 "Radiance". Signal level indicator with peak detector (1 channel). Assembly kit

Remember expensive hi-fi devices in their heyday? Seen peak indicators on professional equipment? This indicator stuck in my memory from my school years.
Let me introduce Project-002. Signal strength indicator with peak detector!

Set contents:

Demo of Datagor-HDTV!

Constructor assembly. A trimmer is installed, then (with polarity observed) capacitors, then (checked with a tester) striped resistors.
I install all the passive elements and slightly extend the legs of the elements with reverse side PP so they don't fall out. Then I solder all the legs at once. I use an inexpensive one soldering station entry level LUKEY-702. The soldering iron has been modified, a separately purchased branded tip has been installed - soldering is a pleasure.
Then I use wire cutters to remove all the excess. Make sure that pieces of metal from under the pliers do not fly into your eye or onto the floor. A piece of thin stem is a great pain in the ass. Be careful, friends!
Lastly, I solder the chip in a DIP22 package. Block R-2 is ready.

Here I want to show alternative option installing LEDs on the back of the board. At the same time, the most high elements The LEDs themselves are obtained on the plane: it is very convenient to adjust the distance from the PCB to the panel of your device. I didn’t cut off the “extra” long legs on purpose so that the LEDs could be removed without loss after finishing the filming of the videos.
Another convenient option- installation of LEDs at an angle of 90° (the legs must be pre-formed). In general, there are a lot of design options for the executive “shining” part - it’s up to your taste, preferences and capabilities.

We unsolder the wires and cascade the two blocks. It is very convenient to use the cable. By cascading, we achieve synchronous operation of the delay systems for displaying the peaks of all combined blocks. Otherwise, due to the imperfection of the elements of timing chains, we would observe confusion and vacillation in this matter.

Photos of assembly options

Sent by Vlad (pmp140). The boards are assembled into a shelf on hexagonal racks, and LED assemblies are connected with a cable.

We ask questions and share experiences on the forum:
Technical support forum for all Datagor Projects

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