This project is intended to indicate the signal strength. This is done using a special LED driver LM3916 (analog signal level meter with display values on the line LEDs). LEDs correspond to the standard values of the scale signal from -20 dB to +3 dB, except 2dB.
Product Overview
Scheme is simple enough, it is almost the same as that contained in the documentation on the chip. In the circuit, the potentiometer is connected to terminals 6, 7, 8, and sets a value of 3 dB. It must be adjusted so that the signal at the input of 0dB 0dB indicator would simply burn. Before entering LM3916 worth transistor BC558. Its purpose is to strengthen the signal to logic 1 level chip. This is achieved by correcting the signal diode 1N4148, then filtering with a capacitor (as he does not pass the DC voltage in the case of hitting it on the input). In principle, this clamp level. 1M resistor is a bleeder resistor. Thus, its value and the value of the capacitor determines the retention level. This is done for fast signaling and its slow decline. The timing and the recession can be adjusted by changing the values of resistor 1M to another.Easy installation of the diode is not used as a direct drop 0,6 V diode cause an error, but the transistor compensates for this fall.
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| LM3916 Audio level meter |
LM3916 can light one LED, respectively. input value, and the LEDs of the column to the bottom of the current value. These modes are switched connection to supply + 9 conclusion (column) or leaving it open (one LED). In column mode, the energy consumption indicator of high enough and it can lead to high currents passing through the GND terminal of the chip. To avoid problems that may arise, use 0.1μF decoupling capacitor in nutrition chip. All conductors desirable to GND as short as possible and finish at the same point. LM3916 can be replacement for LM3915, but the range of measurement would be very limited and will not meet the standard scale signal values.
Technical realization
The scheme has been assembled on the breadboard. Between the LEDs and earth, the tantalum capacitor has been set to filter out interference and leakage that may occur. Indication implemented on the final scale of LEDs but you can use just the LEDs. At the entrance stands the plug from the headphones, LED mode is selected by jumper.
Original article sourse cxem.net