LED volume indicator

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. Due to its design feature, the IC is widely used in LED indicator circuits. Since the LED indicator based on LM3915 operates on a logarithmic scale, it has found practical application 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 a linear characteristic and is ideal for measuring linear quantities (current, voltage), while the 3916 series IC is more universal and is capable of driving different types of loads.

Principle of operation

All level indicators are based on multi-stage comparators.

Comparator – a logical element that compares the parameters of two incoming signals.

The signal being analyzed is supplied to one channel of the comparator, and the reference comparison voltage is supplied to the second. If the amplitude of the first is higher than the reference voltage, a logical one appears at the output, if lower, a logical zero appears.

The operation of the simplest comparator can be demonstrated on the K155LN1 microcircuit, the unit 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 logic 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 based on the lm39xx architecture. This line includes three microcircuits: lm3914, lm3915 and lm3916. Minimal decoupling easily allows you to create an LED sound level indicator with your own hands, even without deep knowledge of radio electronics.

All of them represent a ten-band analyzer. They differ in the way they differentiate the input signal. For lm3914 it is 1V, for lm3915 it is 3dB, for lm3916 it is 1db.

Fixing the missing volume icon in Windows 7

The occurrence of such a problem is often associated with minor system failures, accidental or intentional user actions. There is no universal solution to the difficulty in question, so you just have to try each existing method to find the right one. As always, it’s worth starting with the easy and quick option.

Method 1: Customize notification area icons

First of all, it is recommended to check whether the display of the icon you need is enabled in the notification area settings. Doing this and the following methods is preferable while logged in as an administrator, so if you haven't switched your account yet, it's best to do so now.

After this, you can safely proceed to the implementation of the task:

After performing these steps, you do not need to restart the computer; everything should be activated automatically. However, if this does not happen, you should move on to considering other methods.

Method 2: Restart File Explorer

The standard file manager of the Windows OS family is called Explorer. The behavior of other elements - folders, shortcuts, individual panels and icons - also depends on the correctness of its operation. Sometimes failures occur with this component, which leads to certain consequences. Try restarting it to check if File Explorer is really to blame for the missing volume icon. You will find detailed instructions on this topic in the article below.

If you constantly encounter problems with the functioning of Explorer (it freezes for a while or completely shuts down), it is recommended to fix this problem by changing the operating system settings or eliminating errors.

Method 3: Removing Registry Settings

The Registry Editor stores string and other parameters that determine the values of certain elements, including icons. That is, through this menu, by changing just one digit in any line, you can completely change the behavior of the function, including the display of icons. In most situations, if there is a problem with the Registry Editor, it is due to corrupted parameter values. Therefore, you will need to delete them and restart the computer to restore:

When finished, be sure to restart your PC so that all changes take effect and these settings are restored to their default settings. After that, check if the icon appears in the notification area.

Method 4: Restart the Windows Audio Service

The standard service, which is responsible for the correct operation of audio in the operating system, is, at least indirectly, still connected with the icon we are considering today. If some kind of failure occurs in it or it stops on its own, it is quite possible that the icon will also disappear. This can only be checked by restarting the service.

Another thing to note is that you need to make sure that the service starts in automatic mode. This is done in the same properties menu. If any problems arise with Windows Audio in the future, and the icon disappears again, you will need to resort to additional means of debugging its functioning.

LED audio level indicator on lm3915

Let's assemble a volume indicator on LEDs using comparators on lm3915.

Let's figure out how the scheme works.

The signal being analyzed is received at input 5; its amplitude should be 10V. To match the amplitude of the incoming signal, we need a transistor switch. The analyzed signal is supplied to its base through a resistor voltage divider at R5.

Logical structure of lm3915

The sound indicator on lm3915 can operate in two indication 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 a switch between the common wire and input “9”.