When making my amplifier, I firmly decided to make an 8-10 cell LED output power indicator for each channel (4 channels). There are plenty of schemes of such indicators, you just need to choose according to your parameters. 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 route...

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 ULFs, 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 circuit 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 the resistor Rin, after which we cut off a half-wave with diode D6 and then apply a constant voltage 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 delays the lighting of the last LED for a certain fraction of a second to show that the maximum signal level - peak - has been reached. 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 22 μF at 63 V (I don’t recommend taking it for a lower voltage for ULF with an output of 100 Watt), the 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. Printed circuit board for 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 chain 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 each, we will first debug this circuit for one channel, and it will be very easy to configure others based on it, 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 4-8 Ohm resistor connected instead of the speaker system, although the pleasure of 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.

One day in a friend’s car I saw LEDs flashing to the beat of the music. I was eager to do the same for myself. To begin with, I will decorate the speakers in the computer, and then solder the car. The friend did not know how or what was standing there and blinking. I had to look for something on the Internet myself. One person was very helpful in finding and creating a simple electrical circuit. The circuit contains only 3 parts that can be purchased almost everywhere: an LED, a tuned resistor, and a diode. The circuit diagram itself looks like this:

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.

Hello, friends!

In continuation of the articles on amplifiers, I think the circuit of a logarithmic signal level indicator will also come in handy. This device is based on the LM3915 microcircuit in the amount of two pieces (each microcircuit works on its own channel), you can see detailed information about the microcircuit, the recommended supply voltage is 12V. The LM358 chip acts as a pre-amplifier. Detailed information about the chip.

In place of LM3915, you can use the following similar microcircuits: LM3914 and LM3916. It is worth considering that the jackal chip 3914 is linear, the LEDs light up in steps of 3 dB, and the steps 3915 and 3916 are logarithmic.

In place of LM358, you can use the following similar microcircuits: NE532, OP04, OP221, OP290, OP295, OPA2237, TA75358P, UPC358C.

Advantages of this device

• Easy to manufacture
• Reliability

Flaws

• High cost of the microcircuit. This drawback is eliminated by purchasing radio components in China.

Stereo signal level indicator circuit

Signal level indicator circuit board

List of radio components

Microcircuits. To install microcircuits on the board, I recommend purchasing an additional DIP18 socket and installing the microcircuits into the socket last. In order to reduce the likelihood of failure of the microcircuit due to static electricity when it is installed on the board.

• LM358 — 1 piece
• LM3915 - 2 pcs.

Resistors

• trimming resistor RV1 and RV2 - 100 kOhm - 2 pcs.
• R1, R2 - 22kOhm -2pcs
• R5, R6 - 220 kOhm - 2 pcs
• R3, R4 - 1kOhm - 2 pcs
• R7, R8 - 47kOhm -2 pcs
• R9, R11 - 1.3kOhm -2pcs
• R10, R12 -3.6 kOhm — 2 pcs.

Capacitors

• 1.0 mF - 4 pcs
• electrolytic capacitor 100mF x 32V - 1 piece

• 1N4148 - 4 pcs.
• LEDs - 10 pcs. Selected according to taste with a supply voltage of 3V. We recommend choosing the last two LEDs in a different color.

If you have any questions about this article, please write to the site administrator.

Today, entire electronic devices are used as an indicator of the output signal level for various sound reproduction equipment, which display not only the signal level, but also other useful information. But previously, dial indicators were used for this, which were a type microammeter M476 or M4762. Although I will make a reservation: today some developers also use dial indicators, although they look much more interesting and differ not only in backlighting, but also in design. Getting hold of an old dial indicator might be a problem now. But I had a couple of M4762 from an old Soviet amplifier, and I decided to use them.

On Fig.1 A diagram for one channel is presented. For stereo we will need to assemble two such devices. The signal level indicator is assembled on one transistor T1, any of the series KT315. To increase 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 with similar parameters.
The indicator reading corresponding to the nominal level is set using trimming resistor R2. The integration time of the indicator is 150-350 ms, and the return time of the needle, determined by the discharge time of 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 measuring 100X43 mm (see Fig.2). Indicators are also 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, that’s all the setup of this device comes down to. You may need to select resistor R1 depending on the output signal strength of your device. Because On the other side of the board there are dial indicators; elements Cl, R1 had to be mounted on the side of the printed circuit conductors. It is better to take these parts as miniature as possible, for example, unframed.
Download: Dial indicator of output signal level
If you find broken links, you can leave a comment, and the links will be restored as soon as possible.

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 in the range of 6...20 V. The indicator responds to instantaneous audio voltage values. 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 - the UMZCH speaker system - through the R*/10k divider. 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 the maximum power of the UMZCh.

As you can see, the circuit is simple and does not require complex setup. Due to the wide range of supply voltages, for its operation I used one arm of a pulsed bipolar power supply UMZCH +15 volts. At the signal input, instead of selecting individual resistors, R* installed a 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.