Introduction: LED VU Meter

Picture of LED VU Meter
Yep, another LED VU Meter project.  I had been interested in building this project for a while so I looked over some of the various projects and schematics online and picked one and ordered components that I did not have.  I started building this circuit on a breadboard to make sure it would work.  The initial schematic I used didn't quite work to my satisfaction so I found a simpler one.  Once I tested out the new schematic I tweaked the design a bit for a left channel display and built it into a circuit board.

Here is the data sheet for the chip from Texas Instruments.



The video is a quick demo that the circuit does work.  Pretty nice for my first circuit board!
 

Step 1: What You Will Need:

Picture of What You Will Need:

Check the schematic and x 2 if you want stereo.  You may consider adding a headphones jack, battery holder, voltage regulator if you plan on tapping power from something else, a case to house the final project, etc just depending on how far you want to go with this.  If you look at my first project I installed two similar kits into a vintage boom box.


Step 2: Putting It All Together

Picture of Putting It All Together

Certain components like the light emitting diodes only work if you put them in the right direction.  When you look closely inside the diode you will see that it is divided.  The smaller part is the "+" side and the larger is the "-" side.  If you solder these in backwards they won't work.

Make sure you read up on how to solder components to a circuit board.  And then practice.  This is my first major soldering project so this is my practice.  Many things I could have done better (i.e. the LEDs are not soldered at perfectly the same height and I could have spaced them better on the board).

The main thing is to carefully plan the layout of your board and consider you final application.   That is why I built the circuit many times over on the bread board before committing to something permanent.

Step 3: Progression

Picture of Progression

Knowing that I was going to make a left channel display I knew I would have to attach wires to cross over from right to left.  If you don't want to solder all those wires on the board you can solder the chip on the opposite side of the board.  But not me, I wanted my components on one side, besides, I need the practice.  You can see by the pictures I get a bit better as I go.  The tricky part was figuring out how to connect between two wire posts . . . the better I got at applying the flux and the quicker I could apply just the right amount of solder the better result.  The headphones jack I could have drilled holes to match the posts but I opted to add wire extensions to the posts because I thought that additional hole might weaken the board (It seems I had already drill some holes right down the middle for a previous unfinished project).

Step 4: Almost Done

Picture of Almost Done

Well, done for now.  I hope I left enough room for the right channel (If I ever get back around to it).  The right channel should assemble much quicker because I don't need all the wires crossing over.  The IC chip will go right next to the diodes.

As you can see there is a red wire sticking up next to the headphone jack.  "Red" is for "Right" of course.  The switch comes off of the "-" power line just because it seemed a common point between the two circuits which meet a the headphone jack.

What amazed me about this project is how versatile you can be when you aren't working on a pre-printed board; that really made me feel all the more creative.

Hmm, looking at how my LEDs  get shorter as they go from red to green I imagine they will get longer on the other side as they go from green to red.

Hmm, where am I going to put that pesky 2.2uF 25V 105C Radial Electrolytic Capacitor?

Comments

benco916 (author)2013-08-07

So I followed your diagram and it works but how would I get it into dot mode? I don't have pin 9 connected which is suppose to be dot mode but it seems to be in bar mode for some reason.

Kepster (author)benco9162013-08-08

I actually don't know very much about the chip. I hunted all over to find a VU meter with a low parts count and this is what I came up with. There is quite a bit of good info on the data sheet I only glanced over. http://www.ti.com/lit/ds/symlink/lm3915.pdf There are some slight differences on what components you use between modes.

What I thought was interesting is that you can hook up two of these together and use 20 LEDs. That would be pretty sweet. I'd like to see someone try that and let me know how it turns out!

mikecharlie (author)2013-07-19

nice instructable but would I be able to use a LM3914 instead of the LM3915? I already have 2 of them and hope i can use them instead of buying 2 new chips

Kepster (author)mikecharlie2013-07-19

I'm not sure on that, you would have to look up the data sheets. I'm sure you could try it but I can't guarantee you won't damage your chips. The best thing would be to build it on a breadboard before doing anything permanent. Anything that I put together without a pre-printed circuit board I always build it on the breadboard first so I can more easily further visualize how to plan out my board.

After looking at a couple diagrams, the pins have the same designations. So maybe they will work. If you are concerned about it I'm sure you can find the data sheets with a quick search on the internet.

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