Arrow signal level indicator peaks on the LED. Sound level indicators on led. Technical characteristics of gas discharge indicators
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.
The radio designer came in a bag:
Details: 
The board is one-sided, without metallization, made with high quality, soldering is easy, part designations and denominations are marked: 
The photo shows that the board is different from the board displayed on the seller's lot - there is a J3 connector
Instruction and diagram: 
Scheme in high resolution
Soldered. Here's what happened:
Do not scold for soldering - I have not soldered anything on seals for 27 years. First experience.
There are no extra parts included.
When I soldered, three misunderstandings emerged.
1. It is not clear why there is a jumper connector J3? There is no connector or jumper included in the kit. When turned on, it is somehow incomprehensible that only half of the LEDs (red and below) work. Soldered (shorted) contacts J3
2. Resistor R9. The printout says 560 ohms. In the set - 2.2 kOhm. I installed an MLT resistor from old stocks, as indicated in the diagram - 560 ohms. I thought that the Chinese mixed up something. When turned on, the two lower yellow LEDs - D1, D2 - were constantly on. I soldered the resistor - I took a 2.2 kOhm resistor from the kit - it began to work as it should.
Change in circuit - correct resistor
3. If the extreme red LED lights up and is constantly on, then the resistor R5 starts to heat up to 60 degrees. Weird.
The power supply of the circuit is 9-12 Volts. Apply 12V to power. Everything works fine. The trimmer resistor can be used to set the maximum displayed signal level. The minimum level, if a 1.9 Volt signal is applied to the device: 
Hence the conclusion - at a nominal supply voltage of 9-12 Volts, it is better to connect the indicator to the ULF outputs, and not after the pre-amplifier or to the ULF input after the volume control.
LED glow scale is logarithmic. Can't be used as a low battery indicator. If you connect the headphone output of a cell phone at maximum volume to the input, then a maximum of 6 yellow LEDs will light up.
Then I decided to experiment with reducing the supply voltage. Conclusion - the lower the supply voltage - the more sensitive the device. It worked fine from 5 V - the red LEDs in this case were also on from the cell phone. If the voltage is reduced to 3 volts, the LEDs are dim but do not blink. Apparently this is the limit. So I would not power from a voltage less than 5 volts.
Conclusion: a simple, interesting radio constructor. You can equip them with some homemade ULF. Cons - inconvenient board mounting - only one mounting hole. The board (due to the socket and microcircuit) is quite high. If you put two boards in parallel, then the distance between the LEDs of both channels will be quite large.
Do not replace the arrow indicators of the signal level, light ones are increasingly coming. They can be found in modern high-quality radios, tape recorders, sound reproducing devices.
A simple light indicator can be assembled on several LEDs and transistors. Compared to a pointer indicator, such an indicator will have a large input impedance and high sensitivity, which will allow it to be connected directly to a radio receiver detector or a high-impedance load of an audio frequency signal source.
The diagram of the LED indicator is shown on the 4th page. tabs (Fig. 3). It consists of an amplifier on transistors VT1, VT2 and a "light" scale formed by seven adjacent LEDs (HL1 - HL7).
While there is no input signal, the field-effect transistor VTt is almost closed - this state is determined by the voltage at the source of the transistor, which, in turn, is set by a tuned resistor R4. A small current flows in the drain circuit, and the voltage drop across the resistor R2 is not enough to open the transistor VT2. The setodiodes are off.
When a positive (with respect to the source) voltage is applied to the gate of a field-effect transistor, this transistor opens the stronger, the greater the voltage. Accordingly, the tone of the drain changes, and hence the voltage drop across the resistor R2.
A similar phenomenon is observed in the cascade on the transistor VT2: the greater the voltage drop across the resistor R2, the stronger the transistor opens, the more current flows in its collector circuit. As this current increases, the LEDs HL1 - HL7 alternately light up, starting from the lowest in the circuit. Here's how it goes.
At the moment the collector current of the transistor VT2 appears, it almost completely flows through the resistor R12 and the HL7 saetodiode, creating a voltage drop in this section (at point A relative to the common wire) * At a certain current, the saetodiode flashes, the voltage across it becomes equal to 1.8 ... 1.9 V and does not change with a further increase in current. In other words, the LED becomes a zener diode.
But on the other hand, with increasing current, the voltage at point A will increase. As soon as it reaches the sum of the voltage drops on the “working” LED and the open diode VD6 (0.7 V), i.e. approximately 2.5 ... 2.6 V, the HL6 LED will flash.
The next LED (HL5) will light up with a further increase in the collector current of the transistor VT2, when the voltage at the anode of this saeto diode (at point B) exceeds the sum of the voltage drops on the burning LED and open diodes VD4, VDS. Subsequent LEDs will flash only after an increase in the voltage on their anodes (relative to the common wire) by about 0.7 V compared to the voltage on the anode of the previous (lower in the circuit) with a veto diode.
When the collector current of the transistor VT2 decreases, the LEDs turn off in turn from the top, in sequence, to the bottom.
The LED indicator has a good linearity - this is evidenced by its "amplitude" characteristic, shown in Fig. 2 tabs, - the dependence of the inclusion (ignition) of one or another diode from its then on the input signal level. Linearity is determined both by the accuracy of the selection of resistors R7 - RI2, and by the same parameters of LEDs and diodes.
The indicator is able to work not only from a constant voltage at the input, but also from an audio frequency signal. In this case, it is controlled only by positive half-waves of alternating voltage.
In addition to those indicated in the diagram, transistors KP302A, KP303D KP307B, KP307Zh can be used in the indicator
(VT1), KT208K. KT209A - KT20$K, KT501A - KT501K, KT502A, KT502B (VT2), LEDs AL102A - AL102G, AL307A, AL307B, any diodes of the KD102, KDYUZ, D220 series. D223, D226, KD521. The tuning resistor can be SPZ-1, SP5-2, SP5-16, the remaining resistors are MLT or VS with a power of 0.125 or 0.25 W.
The indicator parts are mounted on a printed circuit board (Fig. 4 on the tab) from one-sided foil
fiberglass. The LEDs are arranged in a row (Fig. I of the tab) so that a kind of light scale is formed when the board is mounted on the front panel of a device, say, a tuner.
Establishing the indicator comes down to setting the trimmer resistor R4 to such a collector current of the transistor VT2 that the HL7 LED barely glows or is on the verge of ignition.
If it is necessary to reduce the sensitivity of the indicator, it is necessary to connect a resistor between its input and the signal source and select its resistance. If the indicator is used to control the audio frequency signal, instead of an additional resistor at the input, a capacitor (KLS, KM-1) with a capacity of approximately 0.033 μF is included, and resistors R7 - R12 take half the values compared to those indicated in the diagram. If the indicator is connected directly to the output of a powerful amplifier, the transistor cascades can be removed altogether by connecting any diode from the above between the left terminal of the resistor R6 according to the circuit and the amplifier output. The cathode of the diode must be connected to a resistor. 
On the 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.
Download: Output Level Gauge
If "broken" links are found, you can leave a comment, and the links will be restored in the near future.
Many sound-reproducing devices, whether tape recorders or amplifiers of the end of the last century, were equipped with a dial indicator on the front panel. His arrow moved to the beat of the music, and although it had no practical significance, it looked very beautiful. Modern equipment, in which compactness and high functionality are in the first place, no longer has such a luxury as a dial sound indicator. However, it is quite possible to find a pointer head now, which means that such an indicator can be easily assembled with your own hands.
Scheme
Its basis is the Soviet K157DA1 microcircuit, a two-channel full-wave rectifier of the average value of signals. The supply voltage of the circuit lies in a wide voltage range, from 12 to 16 volts, because the circuit contains a 9 volt stabilizer (VR1 in the diagram). If you use a stabilizer in a TO-220 metal case, then the voltage can be applied up to 30 volts. Trimmer resistors R1 and R2 regulate the signal level at the input of the microcircuit. The circuit is not critical to the ratings of the components used. You can experiment with the capacitances of capacitors C9, C10, which affect the smoothness of the arrow, as well as with resistors R7 and R8, which set the time for the arrow to reverse. In L and In R in the diagram are connected to a sound source, which can be any device with a line output - be it a computer, player or phone.(downloads: 183)
Circuit Assembly
The indicator board is made by the LUT method on a piece of textolite measuring 30 x 50 mm. Just in case, the microcircuit should be installed in the socket, then it can be replaced at any time. After etching, the board must be tinned, then it will look beautiful from the side of the tracks, and the copper itself will not oxidize. First of all, small parts are soldered - resistors, ceramic capacitors, and only then electrolytic capacitors, tuning resistors, a microcircuit. Lastly, all connecting wires are soldered. The board contains two channels at once and involves the use of two pointer heads - for the right and left channels, however, you can use one pointer head, then the input and output contacts for another channel on the board can simply be left empty, as I did. After installing all the parts on the board, be sure to wash off all the remaining flux, check the adjacent tracks for a short circuit. To connect the board to a signal source, it is most convenient to use a 3.5 jack plug. In this case, if the length of the wires from the board is large (more than 15 cm), a shielded wire should be used.
Pointer head
It is not difficult to find Soviet pointer heads for sale now, there are many types, different shapes and sizes. I used a small M42008 pointer head, it doesn't take up much space and looks nice. Any head with a full deflection current of 10-100 microamps will do for this circuit. To complete the picture, you can also replace the native scale, calibrated in microamps, with a special sound scale, calibrated in decibels. However, it is not necessary to connect the pointer head to the circuit directly, but through a trimming resistor with a nominal value of 1-2 megaohms. Its middle contact is connected to any of the extreme ones and connected to the board, and the remaining contact is connected directly to the head, as seen in the photo below.
