LED Vu Meter – Easy
Overview / how it works:
This circuit uses the LM3916 LED Bargraph driver to give us a real time Volume reading on a set of LED’s.
It takes an input from the audio jack, connected to whatever music source you like, and reads the voltage.
It then works out this voltage as a fraction of the supply voltage and lights the LEDs connected to it accordingly.
You’ll notice the LEDs are all facing into the chip, as supposed to out of the chip, which would seem more intuitive.
However, this chip is using what is called a current sink as supposed to source.
This means instead of producing current on its pins to “drive” an LED, it regulates how much current is let into the chip to turn on an LED.
Effectively you can think about it as the chip varying the resistance between its pins and ground:
when the LED is off there is a high resistance from the pins to ground, and when it is on, there is a lower resistance.
This resistance has also been calculated so we don’t need protection resistors on the LEDs as we would normally.
The potentiometer connected to pin 6 of the chip allows us to vary the “high” trigger for the chip.
This means we can vary the top voltage of the range it is displaying,
so if the music you are playing is quiet, and the voltage from the input is therefore low,
you can use this to “turn up” the display.
Whereas if it is loud, you can compensate and stop the display from being on all the time.
The parts list is as follows:
- One LM3916 LED Driver
- Ten LED’s (we used two red, three yellow and five green)
- One 5.6KΩ Resistor
- One 100KΩ potentiometer
- One 9V battery
- One Battery clip
- One headphone jack
- A breadboard
- Some jumper cables
