Rick’s Awesome Blog

I graduated on April 17, 2008 and I wanted to do something to stand out. I was having trouble thinking of a good idea that could be completed in about three days when it dawned on me. Mix this project with the VU Meter Tie project and kill two birds with one stone. So that’s exactly what I did, and it was awesome. Instead of putting the VU Meter in a Tie, I had the meter going up the front of my gown. Here’s a video of what this all looked like:

Unfortunately, the only video I made of it was with my cell phone, so the quality isn’t that great. Basically, every time I speak the VU Meter jumps. I’ll try to get a better video up as soon as I can. For now, here are the trials and tribulations of this project.

So the first thing I had to do was figure out how the heck to build a VU meter. I figured the best place to look first would be Instructables because that website is awesome for this kind of stuff. After some brief searching I hit pay dirt. This was a whole project about making a VU meter. It was so simple. I really only needed one IC and some LEDs.

The heart of the actual VU meter circuit is the LM3914N IC. A copy of the technical documentation for this IC can be found here. This IC takes an analog input on one pin and then turns a number of pins (0-10) high depending on the voltage it reads on the input pin. You can also change the sensitivity by changing the resistance at another pin. The only local place I could find this IC was Circuit Specialists. I had never heard of them before until the guy at the local Radio Shack pointed me in their direction when Radio Shack once again didn’t have the part I needed. The Circuit Specialists is an awesome place to go if you need a special part and can’t wait for it to arrive in the mail. Once I had the IC I wired up the circuit on a bread board.

The circuit specifically for the VU meter is on the left side. I’ll get to the other stuff next. The LM3914N has all the LEDs set up as common anode. This means that the cathode ends of the LEDs get connected to the chip and the anode ends just get attached to power. I didn’t bother using any resisters since the power I was working with was rather low. Also, I the chip’s max output voltage according to the data sheet is only 1.34 volts, so there really wasn’t anything to worry about. Once the VU meter circuit was set up, I used a male 1/8″ jack plugged into my iPod to test it out. Lo and behold, it worked! One problem I noticed, though, was that the only time all of the LEDs would light up was if the volume on my iPod was turned up all the way. This means that a small microphone would probably not be able to get the lights to turn on at all. I had to build an amplifier circuit.

Doing some Googling lead me to a few good sources about how to use an op-amp, but this PDF was my best resource. I had two op-amps already lying around but the only one I could get working was this LM324N quad op-amp. The data sheet for this chip can be found here. This chip actually has four op-amps built into it and it was much bigger than I needed it. All of the other op-amps I could find locally seemed to require somewhere between 15-25 Volts for operation. This was too much and they would not work for me. The LM324N can actually take anywhere between -0.3V to +32V as the input voltage. Due to my time constraints I just decided to use this chip.

You can see the circuit wired up in the bread board picture on the right side. The two smaller chips on the right are other op-amps that would not work for me. They aren’t in the circuit at all. The LM324N is the larger chip shown. I have it wired up to a small 100kohm potentiometer that you can barely see in the upper right corner. This POT allows me to control the sensitivity of the VU meter. This was crucial since I had no idea how sensitive the microphone would be once I was wearing it. I didn’t want the lights flashing just from the mic rubbing against my clothes.

The last circuit on the bread board can be seen on the bottom right side. That is the microphone circuit. I used a small electret microphone that I pulled out of a Radio Shack amplifier. I tore apart the amplifier a few years ago for a different project. The amplifier was this little plastic thing you could hook onto your belt. It would listen to sound in the room and boost the volume. You could then listen to the sound on headphones if you were hard of hearing. All I used for the project was the microphone. I actually had started out just buying an electret microphone from Radio Shack separately but it wasn’t nearly sensitive enough. The one in the amplifier was absolutely perfect for this project.

At first, I had just hooked up the microphone straight to the circuit. I had the anode pluged into the power rail and the cathode going into the amplifier. This did not work. After some Googling I figured out that these microphones need to be powered. I found this website to be a great help. I wired up the microphone according to one of the schematics on that site and it worked like a charm. It was just sensitive enough. The potentiometer was working as well. Now that everything was working, it was time to solder this thing together.

This is what the top of the circuit board looks like all finished. I used another Radio Shack PCB because they work perfectly for so many small projects. I have used them before and they are just awesome. The closest chip is the op-amp and the farther one is the LED driver. The small round metal thing closest to the camera is the potentiometer. I had to stick a small bent piece of copper wire in the middle of it later to actually be able to adjust the setting.

Here is a closer shot of the board. The 12 pins closest to the camera are used to go to the LEDs. The LEDs are attached to the shirt. Ten of the pins are used for the LEDs, one is left open, and the twelfth is connected directly to the power rail. The closest set of white pins is used for the microphone. I did this so I could remove the microphone from the circuit to use in other projects and for easier storage. The farthest set of white pins is used for the power. I didn’t want to spend 8$ on a tiny power switch so I just used this as a jumper for the main power. The rest of the circuit can best be understood by looking at the schematic.

Here is a nice shot of the bottom of the board. I was so burnt out the night I soldered this. I kept soldering wires to the wrong spot, then moving them, then realizing they were actually in the right spot to begin with. It gets really tricky having to flip the board over so many times. The wires with the black slashes on them were marked so I would know which wires connect the circuits together. Each marked wire starts at one of the circuits and ends at another one. An example would be the wire going from the op-amp circuit to the vu meter circuit.

Here is a blurry picture of the graduation gown with the LEDs attached. It’s the best I have right now. The gown has these flaps of fabric that bend outward from the zipper and go from the collar of the gown, all the way to the bottom. I figured this flap would be perfect to hide all the wiring behind. I took each LED and bent the leads at 90 degree angles. The anode was always on the bottom. I then took a needle and poked two small holes in the fabric on the side of the flap that was right next to the zipper. Then I had to struggle a bit to push the leads of the LEDs through the holes without snagging a thread. Once the LEDs were all inserted, I had to wire them up.

The first thing I did was to attach a wire going from the anode of one LED, to the anode of another LED. I had to attach the anodes of the LEDs into a big chain. Every anode was attached to every other anode, if that makes sense. Just look at the schematic if you get confused. Once that was done, I measured out a length of wire for every LED so that it would just reach the collar of the gown when stretched out. Then I soldered each wire to each cathode of the LEDs. I also had to solder a small plug onto the end of each of the loose wires so I could plug them into the pins on the PCB. There is a picture of what the plugs look like later on. This was a tedious process. I actually ended up burning a small hole into the gown with the soldering iron at once point but it wasn’t very easy to notice. The last thing that had to be soldered an extra wire that would go from one anode, to the power rail on the PCB. The whole chain of wires looked something like this:

You can see all of the LEDs are wired up and the leads covered with electrical tape to prevent shorts. Also, I taped the wires together at certain points to keep them bundled nicely. I didn’t want wires sticking out all over the place. It was about this time that I realized it would have been a good idea to label the wires so I would know which one went to which LED. I had to use my multimeter to help me figure this out, but it was definitely worth it. I labeled the end of each wire with a piece of masking tape and a Sharpie.

Now I had to get the wires from the outside of the gown, to the inside. This had to be done without anything being visible. I just cut a small hole in the gown behind the flap towards the top of the gown. I then threaded through each wire until they were all pulled tight. Here is a shot of the wires going through the hole:

It’s touch to take a picture of. It’s just a bunch of wires going through a hole. Here’s a shot of them coming through the inside of the gown:

Next I needed a way to house the PCB. I didn’t want it just dangling inside the gown because one of the wires would probably break. I didn’t have an enclosure handy and I definitely didn’t want to go buy an over-priced plastic housing from an electronics store. I ended up just duct-taping some cardboard together to make a small box. I cut some slots so I could hook all the wires up, and included a small hole to make room for the potentiometer lever. Here’s what that setup looks like:

Here you can also see the labels I made for the LED wires. The 9V battery fit perfectly in the side of the box. I used a zip tie through the bottom of the box to keep the PCB from falling out in case it somehow got flipped upside down while I was walking. The extra piece of masking tape on the right side was to keep the 9V battery from sliding out and dangling there as well.

Here you can see the battery fitting nice and snug on the right side. Also, the microphone is plugged into the middle section. I’ve removed the LED plugs for a better view.

This is the makeshift potentiometer lever. It’s just a bent piece of copper wire that happens to fit just right into the rectangular slot in the POT. I actually had to tape this lever in place to keep it from falling out. I’ve removed the tape for the sake of the photo.

Now the PCB had a nice housing but it was still just dangling by the wires inside the gown. This was noticeable to onlookers as well as dangerous due to the fact that something could break more easily this way. I tried taping the box to the gown but the tape looked awful from the outside and didn’t hold well enough. Also, I didn’t want to tape it to my shirt and risk damaging the shirt. The solution? A duct tape sash:

That’s me wearing the sash. I just took several pieces of duct tape and attached them together. There were no sticky sides left. I kept the housing down under my arm to be less noticeable. You can also see the microphone clipped to my shirt with an ala gator clip. The black wires were far less noticeable against the black gown.

One last thing I had to do was solder some leads onto the microphone. The mic originally had some tiny stranded wires coming off of it that broke off. I just cut the leads off of a resister and soldered them onto the mic. Then I soldered some longer wire to the leads. The other ends of the wires had the same plugs as the LED wires. This allows me to plug the microphone into the PCB so that I can use it on other projects. It also allows the PCB to be stored easier. Here is a shot of what the plug looks like up close:

The end of the plug fits perfectly on those pins. It is snug enough where I know it wont just fall off, but it is loose enough where I can easily remove them. I used this same type of plug to jump the power switch jumper.

That’s essentially all there is to this project. Unfortunately, I haven’t gotten around to finishing the schematic in Eagle Cad yet, but that will happen very soon. I just have a written copy in my notebook. I will get that schematic finished up and post it right here in the near future. Hopefully, I haven’t forgotten any important details. I also hope to post up some more video soon. My parents were at the graduation with their video camera so they may have some better videos of the VU meter in action. Once I get a hold of that footage I will post another clip or two up here.