The IC has two operating modes DOT mode and BAR mode, also more than one IC can be cascaded to control up to 100 LEDs. For LM3914, the input voltage can vary from 3V to 18V. This IC eliminates the need for programming a microcontroller and also reduces the hardware required to control 10 LEDs. LM3914 is an analog controlled LED driver IC, meaning it can control (turn on or off) 10 LEDs by an analog input voltage. So, In this project, we are going to design a simple Audio Level Indicator (VU meter) using the LM3914N dot/bar display driver IC. More specifically, it helps to visualize analog signals. The solution here was to rasp the top side of the LEDs with rough file, so the light to diffuse more even.An Audio Level Indicator (VU meter) or a volume unit meter, are electronic devices that display the intensity of any Input audio signal, usually in musical pieces of equipment (Drum sets, mic, electric guitars, amps, speakers, etc.). Second drawback is that because of the transparency, the LEDs emit light from one point, which is not very pleasant. There also can be used a black tape around the entire collumn. My solution was to paint the sides of the When one column lights up the adjacent columnsĪlso significantly lights up. For this project Iīought transparent rectangular LEDs, but they have two drawbacks. Levels, yellow for 0dB and red for positive levels. The max input voltage of the LM3916 is set to 1.2V, and with R8-R7 we can adjust the input level. Shorting pins 1-2 will set the bar mode and shorting pins 2-3 will set the dot mode. The output mode can be set with 3-pin jumper JP1. IC2 is connected as precision full wave rectifier and can be any general purpose dual opamp - TL072, TL082, LF353. The formula is Iled = 10 * (1.2V / R1_REF).

The LEDs current is determined by R1_REF, and with 2.2k resistance it will be 5 - 6 mA. The green LEDs usually have little higher forward voltage - 2.2V - 2.4V, so +18V will be sufficient in most cases.

For example if the LED have 1.9V forward voltage and we have 7 LEDs on one pin, then the minimum positive voltage will be 7*1.9V + 1.5V (drop voltage at LM3916) = 14.8V.

The minimum positive rail voltage depends on the voltage of the LEDs. The positive rail must be bellow +25V and combined voltage of negative and positive rails must not exceed 36V. The schematic needs bipolar power supply to work correctly, but the negative rail can be as low as -5V or even -3.3V. Of course LEDs can be soldered directly on the PCB. The LEDs are connected via sockets J3 to J12 (only one row LEDs is shown on the schematic) and I found that it's cheaper to use a 28 pin IC sockets cut in half than regular 40 pin sockets.

Led vu meters