Output level indicator
Today, entire electronic devices are used as an indicator of the output signal level for various sound-reproducing equipment, which display not only the signal level, but also other 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.
Do-it-yourself LED sound indicator. A simple two-transistor circuit that controls the flickering of LEDs for various sounds.
The flicker will match the rhythm or rate of change of the sound. Soldering is quite simple and any inquisitive person armed with a soldering iron can handle the assembly of the circuit. The author shares his experience in the photo and demonstrates the work of the assembled circuit on the video. All parts, together with the printed circuit board, are purchased in the online store at a ridiculous price.
How to assemble a sound indicator with your own hands
A simple circuit with beautiful functionality that allows you to feel the combination of sound and light or become part of an automation, warning or security system, although other applications of the circuit are possible. The operating voltage of the sound indicator is 3-4.5 Volts.
The principle of operation of the sound indicator circuit
The sound indicator circuit includes a microphone sound amplifier and an LED lighting control stage.
- Power is supplied to the circuit through the JP header. The capacitor smooths out voltage fluctuations. Power is supplied to the built-in microphone amplification circuit through resistor R1.
- The amplified signal from the microphone is sent through a 10uF capacitor to the base of transistor Q1. The signal from the collector of transistor Q1 controls transistor Q2.
- Transistor Q2 controls the glow of LEDs D1-D5.
- If a higher supply voltage of the circuit is required, then it is necessary to install an additional resistance with a nominal value of R4 10 ... 100 Ohm in the power circuit.
Circuit Assembly
First you need to unpack the package with parts and check the presence and labeling of parts. You can find out the resistance of resistors, either by measuring the resistance with a tester, or by deciphering it on the marking of the resistor. The ratings and number of parts are shown in the table.
| NO. | Component name | PCB markers | parameter | NUMBER |
| 1 | Resistor | R1 | 4.7K | 1 |
| 2 | Resistor | R2 | 1M | 1 |
| 3 | Resistor | R3 | 10K | 1 |
| 4 | C1 | 47uf | 1 | |
| 5 | electrolytic capacitor | C2 | 1uF | 1 |
| 6 | Transistor S9012 | Q1, Q2 | TO-92 | 2 |
| 7 | Microphone | microphone | 1 | |
| 8 | Light-emitting diode | D1-D7 | 3mm | 5-7 |
| 9 | pin block | 2.54mm 2P | 1 | |
| 10 | printed circuit board | 29*30mm | 1 |
- Assembly can be started in any order. The author began the assembly with the installation of LEDs. The LED has polar electrodes. The installation hint is shown in the photo. It is convenient to install three LEDs first. Solder the leads to the board and cut off the protruding leads with side cutters.
- Next, solder the remaining two LEDs. Transistors are installed according to the key drawn on the board. Electrolytic capacitors also have polarized terminals. The negative electrode is marked on the body, if something is not clear, see.
- We check the correct installation of parts and soldering. We supply power, for example, from three AA batteries. Watch the video of the sound indicator circuit.
Despite its simplicity, on the basis of the circuit, you can assemble a variety of devices, for example:
- signaling device "QUIET" (we install the circuit for highlighting the banner "quieter");
- design a signaling device for the need to clean the computer from dust by increased noise of the processor or video card fan;
- a light signaling device for knocking on the door or manipulating the lock, just lean the microphone against the lock or the front door leaf;
- make a headlight switch in a radio-controlled toy, with the noise of the motor, the headlights will turn on.
A set of parts for assembling the sound LED indicator can be purchased from the following link http://s.click.aliexpress.com/e/eqNvB6y . If you want to seriously practice soldering simple structures, Master recommends purchasing a set of 9 sets, which will greatly save your shipping costs. Here is the link to buy http://ali.pub/2bkb42 . The master has collected all the sets and they have earned.
Good luck and grow your soldering skills.
About a year ago, I got the idea to assemble a 12-220 volt voltage converter. For implementation, a transformer was needed. The search led to the garage, where the Solntsev amplifier was found, which I assembled about 20 years ago. Simply removing the transformer and thus destroying the amplifier did not raise a hand. The idea was born to revive it. In the process of reviving the amplifier, a lot has changed. Including output power indicator. The scheme of the former indicator was cumbersome, assembled on K155LA3, etc. Even the Internet did not help to find it. But another very simple, but no less effective output power indicator circuit was found.
LED indicator scheme
This scheme is well described on the Internet. Here I will only briefly describe (retell) about her work. The output power indicator is assembled on the LM3915 chip. Ten LEDs are connected to the powerful outputs of the comparators of the microcircuit. 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 reacts to the instantaneous values of the sound voltage. The divider of the microcircuit is designed so that each subsequent LED turns on when the input signal voltage increases by 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 acoustic system - through the divider R * / 10k. The range of powers indicated on the diagram 0.2-0.4-0.8-1.6-3-6-12-25-50-100 W is true if the resistance of the resistor R * = 5.6 kOhm for Rn = 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 easy to change display modes. It is enough just to apply voltage to pin 9 of the LM3915 IC, and it will switch from one display mode to another. Contacts 1 and 2 are used for this. If they are connected, then the IC will switch to the "Luminous column" indication mode, if left free - "Running dot". If the indicator will be operated with 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 glows at the maximum power of the UMZCH.
As you can see, the circuit is simple and does not require complex configuration. Due to the wide range of supply voltages for its operation, I used one shoulder of a pulsed bipolar power supply UMZCH +15 volts. At the signal input, instead of selecting individual resistors, R* set a variable resistance of 20 kOhm, which made the indicator universal for acoustics of different impedance.
To change the display modes, I provided for the installation of a jumper or a button with fixation. In the final, he closed with a jumper.
To visualize the signal level, LED indicators built on the architecture of specialized microcircuits are widely used. They are used in a wide variety of devices: indicators of the level of the incoming signal of radio equipment, level indication on an audio amplifier, testers for debugging circuits that use the frequency-pulse principle of load control.
All level indicators are based on multistage comparators.
Comparator - a logic element that compares the parameters of two incoming signals.
The analyzed signal is fed to one channel of the comparator, and the reference voltage of comparison is fed to the second. If the amplitude of the first is higher than the reference voltage, a logical unit appears at the output, if it is lower, a logical zero.
The operation of the simplest comparator can be demonstrated on the K155LN1 microcircuit, the single cluster of which is the "NOT" element.
Such a microcircuit is the simplest logical comparator. When the input voltage is from 0V to 2.4V (which corresponds to a logical zero), the output is 2.7V, as soon as the input voltage exceeds 2.4V, the output signal will drop to zero volts.
There are several chips for level visualization. The most multifunctional circuits, in my opinion, allow you to create microcircuits on the lm39xx architecture. This line includes three microcircuits: lm3914, lm3915 and lm3916. The minimum decoupling easily allows you to create an LED sound level indicator with your own hands, even without deep knowledge in radio electronics.
All of them represent a ten range analyzer. They differ in the way the input signal is differentiated. For lm3914 it is 1V, for lm3915 it is 3dB, for lm3916 it is 1dB.
LED sound level indicator on lm3915
Let's assemble the volume indicator on LEDs using comparators on the lm3915.
Let's see how the circuit works.
The analyzed signal arrives at input 5, its amplitude should be 10V. To pair the amplitude of the incoming signal, we need a transistor switch. The analyzed signal is fed to its base through a resistor voltage divider on R5.
Logic structure lm3915 The sound indicator on the lm3915 can work in two display modes - "dot" and "column". In the first case, the LED corresponding to the current signal level lights up, in the second - all LEDs from zero to the current level. Switching of indication modes is carried out through the switch between the common wire and input "9".
Non-standard application
The indicator using lm3914 can be used as a compact tester for small batteries and accumulators.
The supply voltage of such a circuit is from 5V to 12V. It is convenient to power from the "Krona" or four AAA batteries.
Capacitor C1 - 50 uF 25V, pull-up resistor R1 - 1 MΩ. R2, R3 - 4.7-5 kOhm each. The measurement range of the circuit is 1V with a gradation of 0.1V. R2 adjusts the measurement range, R3 - LED current. If you turn off output 9, the indication will be a "column", but the power elements are quickly discharged.
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
