DIY LED audio frequency indicator. The simplest LED sound indicator. Technical characteristics of gas-discharge indicators
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 output level
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It has now become fashionable to use LEDs and LED matrices for visual indication of signal strength, which was facilitated, to a large extent, by the release of microcircuits of the type. But over time, fashion passes, and you want something original that others don’t have. And here I remember the good old circuit on the gas-discharge indicator IN-13, capable of creating such beautiful effect that any LED would turn pale with envy! IN-13 is a glow discharge indicator in the form of a glass tube 130 mm long.
Pinout of gas-discharge indicators of the IN series
A- anode, E- screen, TO- cathode, Kv- auxiliary cathode, A0- zero anode, A1-A4- group of anodes, Up- the anode is the last.
Technical characteristics of gas-discharge indicators
There are 2 options for sound indicator circuits with IN-13 - a simple one, powered by a 220 V network, and a more complex one - with a DC-DC converter and an operational amplifier at the input.
Sound indicator circuit with inverter
The first circuit is quite old, but quite simple and can be useful to beginning radio amateurs as an indicator of the output signal of the amplifier. You can also use it as a linear voltmeter by slightly changing the input part. A transistor can also be used with some modern high-voltage one.
In my case, I decided to assemble a more complex one, so as not to mess with an unsafe mains power supply. Despite its apparent complexity, it worked almost from the first start.
The entire design, including a 12-120 V step-up inverter to power the anode voltage, fits on one small board. This became possible thanks to the use of SMD parts. Transistors MPSA42 should be high voltage, not ordinary KT315. Replaceable with any with a collector voltage of 200 V or more. Install any similar op-amps - TL062, TL082 and so on.
Setting the sound indicator
The setting comes down to setting the light brightness level using trimming resistor P5. It determines the voltage at the anode of 120 V. Elements P1-4 are needed to set the scale zero and maximum span.
Determining the signal level on indicator LEDs is necessary to solve several problems (current and voltage indicators, phase changes), but most often such a circuit is used specifically to display the sound level.
In modern electronics, indicator LEDs have partly given way to LCD and LED matrices. But a circuit of this type not only clearly shows the signal level, it is also easy to implement and quite visual.
What to assemble an LED level indicator from?
Analog-to-digital converters (ADC) LM3914-16 can be taken as a basis. These chips are capable of driving at least 10 diodes, and with the addition of new chips, the number of light bulbs can increase almost indefinitely. The indicator can have any color, and it is better to think about the design of the case in advance so that it does not become a surprise later.
LM3914 has a linear scale, which can also be used to measure voltage, and 15 and 16 have a logarithmic scale, but the pinout of the microcircuits is no different.
In this case, LEDs can be of any kind, imported or domestic, the main thing is that they are suitable for the task at hand. For example, you can use the simplest AL307 diodes, but you can also use more complex ones.
Calculation of the indicator scheme
Composing this device does not require any special skills. Calculation of current and voltage indicators can be done in any program, like a drawing.
One of the “legs” (9) of the microcircuit is connected to the positive voltage input. This way the LEDs will be controlled as a single column. In order to be able to independently regulate modes when changing phases, the circuit must include a switch, but it can easily do without it if this option is not needed.
The current passing through the LEDs for a given voltage and phase can be calculated as follows:
R – resistance on legs 7 and 8
For a current of 1 mA R=12.5 / 0.001 A = 12.5 kOhm.
And for a current of 20mA R=625 Ohm.
The introduction of a trimming resistor will make it possible to adjust the brightness of the glow; if there is no such need, you can install a regular one. The ratings for them will be 10 kOhm and 1 kOhm, respectively.
The final circuit of the LED level indicator will look something like this.
It is ideal for a mono signal, but for stereo you will have to create another one for the second channel. They can be connected via a regular network cable, taking into account the phase. An excellent option is to make two identical diagrams, made in different colors to demonstrate the level of each channel. Devices can also change their color range, but this implementation will be somewhat more complicated.
The value of C3 can be equal to 1 µF, provided that R4 = 100 kOhm. The R2 rating can be selected from the range of 47-100 kOhm.
This circuit uses a KT 315 transistor, but it can be replaced with any other one with suitable parameters (signal phase, current, voltage phase, p-n junction).
Tip: Everyone necessary elements can be purchased at the radio market or in a store, it is worth considering that LM3915-16 chips are slightly more expensive than LM3914. A less expensive option is to desolder components from existing boards.
The end result will be something like this:
Assembling a signal level indicator on your own is a completely solvable task. The main thing is to find what the circuit will be made of, and then spend a little time checking and debugging the device.
Sound indicator on AN6884 |
The basis of the design is two microassemblies of type AN6884 (KA2284) - this is a ready-made LED signal level indicator used to indicate various values of an alternating signal, to which it remains to connect a few components of the harness and the LEDs themselves. The diagram of such a device is precisely shown in the figure below.
Photos of assembled and soldered printed circuit board You can see it in the figure below, and you can take its drawing made in the Sprint Layout program from the green link above.
The basis of the operational amplifier design is LM324. This circuit uses two quadraphonic operational amplifier, to form eight slave audio frequency channels.
Another interesting option circuits of 10 LM324 chips and 40 LEDs. If you assemble two identical structures, you can use them in stereo mode. Supply voltage 12 V, current consumption 2.5A
The range of the sound level indicator (ULF power) should be in the range from 0.5 to 50 W. A special feature of the device is that it does not require an external power supply; it receives its volts from the incoming audio signal.
The basis of the circuit is the LM339 chip, which is a quad comparator. The voltage going to the indicator input is doubled using diodes VD1 and VD2 and capacitors C1 and C2, then it goes to the 78L05 stabilizer used to power the LM339 op-amp and to the inverse inputs of the comparators through a voltage divider on resistors R6 and R7. Using tuning resistances R2-R5, each comparator is adjusted to operate at any required level. When the comparator is triggered, the corresponding LED lights up.
LED sound indicator on the A227D chip (K1003PP1) |
Basic device parameters
Circuit supply voltage: 10-18 V
Input voltage at pins 3,16,17, max 6.2 V
U input 50-500 mV
With resistance R6 we adjust the brightness of the LEDs. Using resistor R8 we adjust the lighting level of the first LED. R10 - too, only for the last LED. The integrating chain R4, C3 sets the delay time for turning off the LEDs.
The basis of the simple design is the AN6884 chip, which is an almost ready-made signal level indicator. You can also use a transistor version of the device, but you will need many transistors and the effect will be an order of magnitude worse, and the sensitivity will be generally lower.
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 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 microcircuit.
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.
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