Featured User: kurt
Open-source hardware project hosting is my passion. I spend most of my free time building neat gadgets or planning what I'll build next. I love building things, and I want to make Open Hardware Hub a place that inspires others to build, ...
Updates 2013 February 18
It's been a while, hasn't it? Well, that's ok because we've got a lot of updates to talk about. Most of these have been effective on the site fora couple weeks now. A few may or may not be active when this article gets posted, but they'll certainly be applied in the ...
Mono VU Meter
A VU meter is used to display the loudness of an audio signal. This open source VU meter lights up ten LEDs to show how loud a mono audio signal is. Two of these can be made to show the loudness of each channel in a stereo signal.
Bill of Materials
|Qty||Part #||Description||Schematic ID||Source|
|1||SJ1-3523N||CONN JACK STEREO R/A 3PIN 3.5MM||J1||Source|
|1||BS6I||SNAPS 9V 6" LEADS I-STYLE||JP1||Source|
|1||50-0015-00||SWITCH PB SPST ALT ACT PC MOUNT||S1||Source|
|1||SK100M035ST||CAPACITOR ALUM ELEC 10UF, 35V, RADIAL||C1||Source|
|1||EVN-D8AA03B14||TRIMMER 10K OHM 0.1W TH||P1||Source|
|1||LM3916N-1||LED BAR GRAPH DRIVER, 3916, DIP18||IC1||Source|
|10||WP7113LID||5MM LOW CURRENT RED LED, LAMP THOLE, BULK||LED1, LED2, LED3, LED4, LED5, LED6, LED7, LED8, LED9, LED10||Source|
|1||6LR61XWA/1SB||BATTERY IND ALKALINE 9 VOLT||Source|
|1||Y-Audio Cable||6inch 3.5mm Stereo Jack/Two 3.5mm Stereo Plug Cable||Source|
Get your LM3916 and breadboard ready. Make sure you have all the parts in the parts list.
Collect your 10 LEDs. You can use any color LEDs that you would like. One common arrangement is LEDs 1-7: green, LEDs 8-9: yellow, LED 10: red. I used just red LEDs.
Insert the first LED as shown. The positive leg of the LED (the long leg) connects to the red wire. The short leg goes to the LM3916 IC.
Insert the second LED. The long, positive leg goes connects to the +9V rail on the far right side of the bread board. All of the following LEDs also have their long, positive legs connected to this rail.
Insert the fourth LED. I'm making the LED alternate left and right so that they can squeeze together.
Insert the 10uF capacitor as shown. The negative leg of the capacitor (indicated by the white stripe on the side of the case) connects to pin 2 of the LM3916 IC. The positive leg connects to pin 3.
Insert the trim pot (potentiometer) as shown. In this circuit, the trim pot serves a dual role. It adjusts the brightness of the LEDs as well as the maximum range of the VU meter itself.
Insert a red wire into the rail that the LEDs are plugged in to. This will serve as the +9V rail. Plug a green wire into the other rail. The green wire will be ground for this circuit.
Solder a pair of wires to the audio jack as shown. The longer terminal in the middle is the reference gound. The other two pins are stereo-left and right. You audio jack may look differently. The pin in the middle/the pin that looks different is usually the reference ground.
It doesn't matter if you use stereo left or right. If you build another VU meter, then you can display stero left on one and stereo right on the other.
Connect one of the audio jack's terminals to ground and the other to pin 5 of the LM3916. It doesn't matter which terminal of the audio jack goes where because the audio signal is AC and the IC only measures the peak voltages.
Plug the other end of the audio cable into a Y-splitter. The male end of the Y-splitter plugs into your PC/iPod. The female end let's you plug in your headphones/speakers.
Connect a pair of alligator clips to the ground and +9V wires. I used a set of black clips for ground so I could remember which clip was which polarity. You could also use a 9V clip instead of alligator clips for this step. (Connect the red wire to the right-hand rail and the black wire to the left-hand rail.)
Connect the ground alligator clip to the (-) side of the 9V battery, and the +9V alligator clip to the (+) side of the battery. If you are using a 9V battery clip, simply snap it onto your 9V battery.
At this point, all of the LEDs may or may not light up. Plug the Y-splitter in to your PC and play some music. Adjust the trimpot with a small flathead screwdriver so that the loudest parts of songs just barely light up all the LEDs.
Enjoy your new VU meter and show it off to all your friends! Check out http://youtu.be/LT-YHW8Z-L8 to see my VU meter at work.
7 - updated description
5 - added youtube link. updated line numbers.
4 - changed LED part
3 - added description to project image
2 - added file descriptions
1 - Initial project release
blog comments powered by Disqus