Peak output power indicator. Peak level indicator

LM3915 – integrated circuit(IC) manufactured by Texas Instruments, responds to changes in the input signal and outputs a signal to one or several of its outputs. Thanks to its design feature ICs have become widespread in LED indicator circuits. Since the LED indicator based on LM3915 operates on a logarithmic scale, it found practical use in displaying and monitoring the signal level in audio amplifiers.

The LM3915 should not be confused with its relatives LM3914 and LM3916, which have a similar layout and pin assignment. The 3914 series IC is linear and ideal for measuring linear quantities(current, voltage), and the 3916 series IC is more universal and is capable of managing different types of loads.

Brief description of LM3915

The block diagram of LM3915 consists of ten similar operational amplifiers, working on the principle of a comparator. The direct inputs of the op-amp are connected through a chain of resistive dividers with different resistance values. Thanks to this, the LEDs in the load light up according to a logarithmic dependence. Comes to inverse inputs input signal, which is processed by the buffer op-amp (pin 5).

The internal structure of the IC includes a low-power integrated stabilizer connected to pins 3, 7, 8 and a device for setting the glow mode (pin 9). The supply voltage range is 3–25V. The reference voltage can be set in the range from 1.2 to 12V using external resistors. The entire scale corresponds to a signal level of 30 dB in 3 dB steps. The output current can be set from 1 to 30 mA.

Sound indicator circuit and principle of its operation

As can be seen from the figure, the fundamental electrical diagram The sound level indicator consists of two capacitors, nine resistors and a microcircuit for which ten LEDs serve as the load. For easy connection of power and audio signals, it can be supplemented with two solder connectors. Anyone, even a beginner radio amateur, can assemble such a simple device.

A typical connection provides power from a 12V source, which is supplied to the third pin of the LM3915. It, through the current-limiting resistor R2 and two filter capacitors C1 and C2, goes to the LEDs. Resistors R1 and R8 serve to reduce the brightness of the last two red LEDs and are optional. 12V also comes to the jumper, which controls the operating mode of the IC through pin 9. In the open state, the circuit operates in the “point” mode, i.e. one LED corresponding to the input signal lights up. Closing the jumper switches the circuit to the “column” mode, when the input signal level is proportional to the height of the illuminated column.

A resistive divider assembled at R3, R4 and R7 limits the input signal level. More fine tuning carried out by multi-turn trimmer resistor R4. Resistor R9 sets the bias for top level(pin 6), exact value which is determined by resistance R6. The lower level (pin 4) is connected to the common wire. Resistor R5 (pin 7.8) increases the reference voltage and affects the brightness of the LEDs. It is R5 that sets the current through the LEDs and is calculated using the formula:

R5=12.5/I LED, where I LED is the current of one LED, A.

The sound level indicator works as follows. The moment the input signal crosses the threshold lower level plus the resistance at the direct input of the first comparator, the first LED (pin 1) will light up. Further growth sound signal will lead to alternate operation of the comparators, which will be indicated by the corresponding LED. To avoid overheating of the IC case, the LED current should not exceed 20 mA. Still, this is an indicator, not a New Year's garland.

Printed circuit board and assembly parts

The printed circuit board of the sound level indicator in lay format can be downloaded. It has dimensions 65x28 mm. Assembly requires precision parts. Resistors type MLT-0.125W:

R1, R5 R8 – 1 kOhm;
R2 – 100 Ohm;
R3 – 10 kOhm;
R4 – 50 kOhm, any trimmer;
R6 – 560 Ohm;
R7 – 10 Ohm;
R9 – 20 kOhm.

Capacitors C1, C2 – 0.1 µF. It is recommended to solder the LM3915 IC not directly, but through a special socket for the chip. The load can use ultra-bright LEDs of any color, even purple. But these are personal aesthetic preferences. To display a stereo signal, you will need two identical boards with independent inputs. More details about the LM3915 can be found in technical description Here.

Performance of this indicator has been proven in practice by many amateur radio circles and is still available in the form of MasterKits.

Read also

Picture 1.

We present to your attention a two-channel (stereo) level indicator with a peak detector from Ondrej Slovak. This indicator was developed on the PIC16F88 microcontroller; it can also be assembled on the PIC16F1827 microcontroller and on the PIC16F819 microcontroller. The peak indicator firmware for all these types of microcontrollers is in the attachment (archived). The circuits are similar, only the firmware differs. We will consider a circuit with a PIC16F88 microcontroller.
The display of levels and peaks in the indicator occurs on two LED scales (rulers) of 16 LEDs each, 2 x 16.
The modes in which the indicator can operate are shown in the table below; they are the same as in the previous diagram (indicator). They can be combined and combined by installing or removing jumpers. Resistor R1 changes the sensitivity of the indicator, changes the voltage at pin 2 of the microcontroller, and the lower the voltage at pin 2, the higher the sensitivity of the indicator. The optimal output voltage is within 200-250 mV.

Table 1.Selecting display modes.

The indicator scale operates in two display modes: linear and logarithmic (below in the figure). The linear scale is programmed in the program code, but the values of the logarithmic scale can be changed at your discretion, or even made inverse logarithmic. This data is “hardwired” into EEPROM and can be changed.

Figure 2.

We'll look at how to change the EEPROM data values yourself below.
Figure 3 shows a “snapshot” of the EEPROM codes of the ISPROG program.

Figure 3.

At the top of the table, the lines circled in red are the (logarithmic) “ignition” values of each LED (16 values), which correspond to the value of the logarithmic scale in Figure No. 2. This hexadecimal values vertical scale (from 2 to 248). You can build your own scale, for example an inverse logarithmic scale, and enter your values in these cells.
Further below we will analyze it in parts;
03 - The first value is the LED glow time, the default is 12 ms (1 = 4.096 ms, that is, 03 = (4.096*3) = 12.228 ms)
08 - This is the last LED light time, default 33 ms.
08 - This is the decay rate of the peaks, the default is 33 ms.
7A - This is the peak persistence time, the default is 500 ms. (7A = 122 * 4.096)
64 - This is a correction for the brightness of the LEDs. For LEDs with a glow current of 2 mA - the value is 64, for LEDs with a glow current of 20 mA - set to 08.

Watch a demo video of how the peak indicator works. Here it operates in display mode with peaks in falling mode, the scale is logarithmic (jumpers removed).

Configuration of the PIC16F88 processor (installation of fuses, fuses).
CP:OFF, CCPMux:RB0, Debugger:OFF, WRT:Writable, CPD:OFF, LVP:OFF, BOREN:ON, MCLRE:I/O, PWRTE:Disabled, WDTE:ON, OSC:INTRC-I/O, IESO:OFF, FCMEN:OFF

Configuration of the PIC16F1827 processor (installation of fuses, fuses).
FOSC:INTOSC, WDTE:ON, PWRTE:OFF, MCLRE:OFF, CP:OFF, CPD:OFF, BOREN:ON, CLKOUTEN:OFF, IESO:OFF, FCMEN:OFF, WRT:OFF, PLLEN:OFF, STVREN: OFF, BORV:HI, LVP:ON

Attached in the archive, there are also the initial parts of the asm codes for these processors, which indicate the processor configurations.

*When designing and setting up his developments on microcontrollers, the author uses the PRESTO USB programmer and, accordingly, the accompanying software software ASIX company - ASIX UP program. Processor configurations are specified for this program.
I repeated this design using the ExtraPic programmer and the icprog program. I did not install or control processor configurations. Immediately after the firmware, the circuits started working (I also mean the first circuit for 40 LEDs), I repeated it several times - everything started working immediately after the firmware.

Figure 4.

The indicator is assembled on a printed circuit board measuring 84 x 27 mm. Photo printed circuit board below in figure No. 5. On the board there are resistors R1-R8 smd.

Figure 5.

Below, Figure 6 shows jumpers soldered on the board between the LED lines.

Figure 6.

Appearance collected indicator. The board contains flat LEDs, resistors R1 - R8 of the smd type, soldered to reverse side boards, from the side of the tracks.

Figure 7.

The printed circuit board of the indicator (in Sprint-Layout format is available in the archive) with the arrangement of elements is shown in Figure No. 8. The board does not indicate jumpers between the lines of LEDs, since they are located one above the other. The jumpers are soldered to places indicated by numbers 1 - 7, and first jumper No. 1 is installed in place 1-1, then jumper 2 is installed in place 2-2, etc.

Figure 8.

Below in the archive there is a diagram, drawings of a printed circuit board in Sprint-Layout format, firmware for microcontrollers PIC16F88, PIC16F1827, also a printed circuit board in Sprint-Layout format with an increased distance between the rows of LEDs and designed for the installation of round LEDs has been added to the archive, as well as firmware for PIC16F819 microcontroller.

If anyone has any questions about the design of the indicator, please ask.

When making my amplifier, I firmly decided to make 8-10 cells LED indicator output power per channel (4 channels). There are plenty of schemes of such indicators, you just need to choose according to your parameters. On this moment selection of chips on which you can assemble an output indicator ULF power, 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 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 display 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 pressure applied to the input of each cell. The indication cell represents the threshold key device which lights up the LED when a certain input level is reached.

Capacitor C1 is needed to ensure 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 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 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 since the cells are identical and you can’t special effort You will figure out what and where to solder.

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, 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))

We are achieving variable resistor confident LED glow 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.

We present to your attention a two-channel (stereo) level indicator with a peak detector from Ondřej Slovák. This indicator was developed on the PIC16F88 microcontroller; it can also be assembled on the PIC16F1827 microcontroller and on the PIC16F819 microcontroller. The peak indicator firmware for all these types of microcontrollers is in the attachment (archived). The circuits are similar, only the firmware differs. We will consider a circuit with a PIC16F88 microcontroller.
The display of levels and peaks in the indicator occurs on two LED scales (rulers) of 16 LEDs each, 2 x 16.
The modes in which the indicator can operate are shown in the table below; they are the same as in the previous diagram (indicator). They can be combined and combined by installing or removing jumpers. Resistor R1 changes the sensitivity of the indicator, changes the voltage at pin 2 of the microcontroller, and the lower the voltage at pin 2, the higher the sensitivity of the indicator. The optimal output voltage is within 200-250 mV.

Table 1.Selecting display modes.

Figure 2.

We'll look at how to change the EEPROM data values yourself below.
Figure 3 shows a “snapshot” of the EEPROM codes of the ISPROG program.

Figure 3.

At the top of the table, the lines circled in red are the (logarithmic) “ignition” values of each LED (16 values), which correspond to the value of the logarithmic scale in Figure No. 2. These are hexadecimal vertical scale values (from 2 to 248). You can build your own scale, for example an inverse logarithmic scale, and enter your values in these cells.
Further below we will analyze it in parts;
03 - The first value is the LED glow time, the default is 12 ms (1 = 4.096 ms, that is, 03 = (4.096*3) = 12.228 ms)
08 - This is the last LED light time, default 33 ms.
08 - This is the decay rate of the peaks, the default is 33 ms.
7A - This is the peak persistence time, the default is 500 ms. (7A = 122 * 4.096)
64 - This is a correction for the brightness of the LEDs. For LEDs with a glow current of 2 mA - the value is 64, for LEDs with a glow current of 20 mA - set to 08.

Watch a demo video of how the peak indicator works. Here it operates in display mode with peaks in falling mode, the scale is logarithmic (jumpers removed).

The indicator diagram is shown below in Figure 4. The LEDs are used for a current of 3 mA, if you install more powerful LEDs, for a current of 20 mA, then resistors R1-R8 must be replaced with resistors of 22-33 Ohms, you can install SMD resistors on the board. To quickly switch operating modes of the indicator, switched jumpers (“jumpers”) are installed on the board.
Configuration of the PIC16F88 processor (installation of fuses, fuses).
CP:OFF, CCPMux:RB0, Debugger:OFF, WRT:Writable, CPD:OFF, LVP:OFF, BOREN:ON, MCLRE:I/O, PWRTE:Disabled, WDTE:ON, OSC:INTRC-I/O, IESO:OFF, FCMEN:OFF
Configuration of the PIC16F1827 processor (installation of fuses, fuses).
FOSC:INTOSC, WDTE:ON, PWRTE:OFF, MCLRE:OFF, CP:OFF, CPD:OFF, BOREN:ON, CLKOUTEN:OFF, IESO:OFF, FCMEN:OFF, WRT:OFF, PLLEN:OFF, STVREN: OFF, BORV:HI, LVP:ON
Attached in the archive, there are also the initial parts of the asm codes for these processors, which indicate the processor configurations.
*When designing and setting up his developments on microcontrollers, the author uses the PRESTO USB programmer and, accordingly, the accompanying ASIX software - the ASIX UP program. Processor configurations are specified for this program.
I repeated this design using the ExtraPic programmer and the icprog program. I did not install or control processor configurations. Immediately after the firmware, the circuits started working (I also mean the first circuit for 40 LEDs), I repeated it several times - everything started working immediately after the firmware.

Figure 4.

The indicator is assembled on a printed circuit board measuring 84 x 27 mm. Photo of the printed circuit board below in Figure No. 5. On the board there are resistors R1-R8 smd.

Figure 5.

Below, Figure 6 shows jumpers soldered on the board between the LED lines.

Figure 6.

Appearance of the assembled indicator. The board has flat LEDs, resistors R1 - R8 of the smd type, soldered on the back side of the board, on the side of the tracks.

Figure 7.