Simple Cheap VU Meter

I've been wanting to post this for a while but I never had the time.

Here is the original.

Basically, a while ago I wanted to make a VU meter (because they are awesome).
I went through multiple designs, and this one was the one that I liked the most. So far, I have not found any other VU circuit as simple as this. If you find one, show me!

First of all, the parts...

• Some PCB (if you can get those fiberglass PCBs, LEDs look so much cooler in more transparent PCB)
• 10xBlue SMD LEDs (specific one in the pictures)
• 1xLM3914/3915/3916
• 2x3.5mm Audio plug
• 1x3.5mm Audio plug male-male ends
• 5v power source (USB, battery, etc.)
• Clear nail polish
• 2 pin header (for 5v power)

Here is a video of an older version of the VU meter (I have three versions). You might like this design better?
 

I did not mention that you needed resistors. In the photo I have resistors: the function of them is to scale down the current going from input to output audio plugs.

In order for the VU meter to be simple as possible and run on 5v (rather than most projects at 6v), I did not include an amplifier circuit. Instead, you will have to turn up your music a little higher for the VU meter to respond. The resistors will serve to lower that volume to what you want it to be when you listen to it.
I would use a resistance from 200-400 ohms. Remember that this is a resistor, and not a voltage divider.

Okay, so attached is a simple schematic, and the design. Download this awesome free PCB software to view the file!
Remember to print BLACK ink, HIGH quality, ACTUAL SIZE.

 

Okay, so once that is printed, cut a photosensitive PCB to that size

Here is where I get my PCB stuff.

Now that it is cut, quickly peel off the protective layer, align the transparency onto the board (please note that I added text on the copper so that you will know how to orient the transparency), put a piece of plexiglass to flatten the sheets, and place a lamp on top of the sandwich.

Do this quickly, but it's ok if you are a bit slow: get it right the first time.

After about 8 minutes...

This is pretty straight forward. After 8 minutes pass, take the board quickly and throw it into the developer. Agitate the mix by moving it around a bit.

After it has fully developed, clean up the board to check for impurities. If all is well, put it in the etchant! This part might take a while if your etchant is old, like mine.

side note
My etchant is from Kinsten which is
[quote]
"EB-750 etchant is Sodium Persulphate, and it reacts with copper to become Copper Sulphate." 
[/quote]

Turns out, from this instructables that I can use it for electroplating! I would do this in a fume hood or outdoors; the fumes are odorless but that can cause you to choke.

 

After you are done etching, take the board out and rinse it.

You can store etchant and developer to reuse; use plastic or glass container.

Clean the board with some acetone, goof-off (too heavy duty though), or nail polish remover.
After, drill holes with a dremel rotary drill.

side note
Recently, all my drill bits have been breaking like crazy. This really put a damper on my projects. I bought a bunch of new drill bits and I reccomend steel drill bits. They drill extremely quickly.
I'm not sure if this link will work in the next week, month, or year, but here it is.


After drilling, sand out the edges.
After sanding, prepare tweezers and your LEDs.
For these LEDs, the side with the notch is the negative end.
Solder one pad of all the LEDs on the PCB.

So, I will also teach you how to solder SMD components (with a small amount of leads)

In general, you want to only add solder to one pad, and secure the component on that single pad.
After that component is secure, solder the rest of the pads.

For something like a four sided QFP chip, solder one corner of the chip, then the opposite corner, then the other corners, then finish everything else.
(check this instructables for the lazy way)

Look at the pictures; they are worth thousands of words.
 

So, now that your board is finished, test it out on your audio player!

From my previous VU meter versions, I used USB power which worked perfectly. Recently I discovered that I can also power it from this battery from this project.
What's really cool is that you can pair up these two devices and have an awesome audio player!

So, once you verify that it works, you want to make it last, 
so clean the PCB with alcohol to remove ugly goop from flux, and cover it in glossy clear nail polish.

Congrats, and enjoy your self made VU meter!