Homemade block Peak indication of a stereo signal with your own hands, circuit of a simple peak indicator. Peak indicators of audio signals indicate the fact that the AF signal level exceeds a certain preset value.
Here is a description of the peak LED indicator based on the CD4093 chip. The domestic analogue of which is K561TL1. The microcircuit contains four logical elements “2I-Not” with the effect of Schmitt triggers. In this circuit, the inputs of each of the elements are connected to each other, so the elements work as inverters - Schmitt triggers.
Schematic diagram
The output signals of stereo channels from the ULF output are supplied through capacitors C1 and C2 to the inputs of elements D1.1 and D1.2, respectively. The inputs of these elements through resistors R2 and R3 receive constant pressure offset from trimming resistor R1.
At the inputs of logic elements, the DC offset voltage is added to the AC component of the audio signal. The task of resistor R1 is to set the optimal bias voltage at which the required sensitivity of the indicator will be, that is, this resistor sets the same peak threshold.
Rice. 1. Schematic diagram homemade peak indicator.
The state at the outputs of elements D1.1 and D1.2 will change only when this threshold is exceeded; the set value of this circuit is converted into logic level pulses, which charge capacitors C3 and C4 through diodes VD1 and VD2. These circuits of diodes VD1, VD2, capacitors C3, C4 and resistors R4, R6 work as detectors.
And the voltage on capacitors C3 and C4 increases. This is especially important since the peak moment of the input signal may not last long. And the voltage in the form of charge is retained by these capacitors because they are charged quickly through the diodes and discharged slowly through the resistors.
As soon as the voltage at C3 or C4 reaches the switching threshold of the Schmitt trigger (D1.3 or D1.4, respectively), a logical zero appears at the output of D1.3 or D1.4, which causes the HL1 or HL2 LED to light up. The corresponding LED, or if the stereo signal is well balanced, both LEDs flash and remain on for at least the time required to discharge C3 or C4 through R4 or R6.
Details and setup
LEDs - any indicator, for example, AL307. Setting up - adjusting resistor R1 according to the operating threshold.
LM3915 is an integrated circuit (IC) manufactured by Texas Instruments that 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. Because led indicator based on LM3915 works on a logarithmic scale, he 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 has linear characteristic 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 LM3915 block diagram consists of ten identical operational amplifiers operating on the comparator principle. 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. The inverse inputs receive an input signal, which is processed by a 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, the load for which is ten LEDs. 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 precise adjustment is carried out by multi-turn trimming resistor R4. Resistor R9 sets the bias for the upper 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. At the moment when the input signal overcomes the lower level threshold plus the resistance at the direct input of the first comparator, the first LED (pin 1) will light up. A further increase in the sound signal will lead to the comparators being activated one by one, 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.
The performance of this indicator has been proven in practice by many amateur radio clubs and is still available in the form of MasterKits.
Read also
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 chip failure due to impact static electricity when installing it 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, as an indicator of the output signal level for various sound reproduction equipment, entire electronic devices, 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
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This kit will allow you to assemble an LED indicator of the UMZCH power output. The device allows you to roughly estimate the output power of the amplifier during its operation. And if there are several channels, then identify possible imbalances in their work. In addition, it will liven up the front panel of your amplifier.
The indicator is made on a specialized chip LM3915N, which is led driver with internal buffer amplifier, comparator and voltage reference. The principle of operation of the microcircuit is based on comparing the magnitude of the input signal with an internal reference voltage source. To expand the range of input voltages, the microcircuit is equipped with a programmable divider R5, R6.
Resistor R7 limits the current passing through the LEDs and thus facilitates the thermal operation of the microcircuit.
A peak detector is assembled on transistor VT1, which allows you to increase the accuracy of measuring the input signal and prevent flickering of the LEDs during transient values of the signal value.
Resistor R1 can be used to adjust the sensitivity of the indicator within small limits and take into account the ULF load resistance.
Jumper JP1 switches the microcircuit display mode - “dot” or “ruler”. In the first case, the magnitude of the input signal is displayed by one LED, in the second, the microcircuit forms a luminous column of LEDs.
Characteristics:
Number of displayed power levels: 10 pcs.;
Rated supply voltage: DC 12 V;
Rated current consumption (silent mode): 10 mA;
Minimum displayed signal value: -27 dB;
Maximum displayed signal value: 0 dB;
Input impedance: 100 kOhm;
Assembly difficulty: 1 point;
Assembly time: About 1 hour;
Operating temperature range: 0...+45 degrees Celsius;
Relative humidity: 5...95% (without condensation);
Device dimensions: 56 x 46 x 17 mm;
Total weight of the set: ~35 g.
Contents of delivery:
Printed circuit board;
A set of radio components;
Roll of tubular solder POS-61 (0.5 m);
Operating instructions.
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