Introduction: Simple 20 LED VU Meter + Datasheet Guide

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About: Hi, I'm Matej and I'm a student of Electrical Engineering. I have been working with electronics for more than 7 years and have lots of knowledge, projects and lots to share along my path, so this page is just …

Hi all. In

this instructable, I’m going to show you how to make a nice 20 LED VU meter with minimal parts and effort. I’ll show you how datasheet is a very strong and viable tool to work with on your project instead on relying on others(projects).

Everyone knows about a VU meter and for an electronic enthusiast is like an amplifier and a speaker, everyone makes one because it’s fun to look at and you can use it by your radio or amplifier speaker combo.

So it’s popular by these 10 LED ones but for professionals, those don’t give much resolution. But even for us, it can be dull and having that extra more is much cooler and doesn’t cost that much more.

So I searched Instructable for a 20 LED VU meter or some sort but with no result. So I decided to make my own. I made 3 of these for a Museum’s exhibition about a month ago with schematics from some book or article that I’ll be including in the end, but for this project, I want to dig into selected IC datasheet. I’ll make a list of parts, buy them and assemble the circuit. I’ll also be having some video footage for a change.

Step 1: Finding the Main IC

So in order to make this VU meter, I’ll be

resorting to al analog circuitry without any Arduino microcontrollers as that would be another project for another time. So the IC of choice is one of LM3914 / LM3915 / LM3916. Now, you have probably herd of all of them or at least the LM3915 as they are all used for VU meter and alike projects. But as they are different models one would assume that they have different purpose. And you would be partly correct. They CAN be used for the same purpose like I used just LM3915s for those VU meters that I told about but let’s look at the datasheet for an explanation. I used Texas Instrument datasheet page for these parts.

LM3914

“The LM3914 is a monolithic integrated circuit senses analog voltage levels and drives 10 LEDs, providing a linear analog display.”

This is a quote from the datasheet. What it means is that it’s an IC that senses different voltage levels and linearly displays those voltage levels on 10 LED. This is used as a voltage level meter by its linear nature giving exact results if you configure it right. Input signal is also limited from 0V to 5V.

LM3915

“The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs, LCDs or vacuum fluorescent displays, providing a logarithmic 3 dB/step analog display.”

So as you can see, the description doesn’t change much as these are same parts, but with each one comes an upgrade of some sort. In this case, the LM3915 also senses analog voltage levels but provides logarithmic scale of driving those 10 LEDs. Also it has defined 3dB/step or LED value for precise displaying of voltage input. And as it is logarithmic as our hearing, meaning that we can distinguish better differences in lower volumes than in higher (see the graph), so it is better used for audio applications. In the same description it also describes how it can be used as a VU meter.

LM3916

“The LM3916 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs, vacuum fluorescent displays, providing an electronic version of the popular VU meter.”

The description for LM3915 is quite the same as well as the one from LM3915 but it also mentions right from the start that is very good to use as a VU meter. This can convince more people to go with this version as it mentions VU meter from the start. Not that previous version cannot do the same. They do, but they are not precisely made and “calibrated” for the scale of VU meter. But many people building these don’t really need accuracy and just want LEDs to “dance” to music.

CHOISE

So, what did I pick. I’m going to be the one to say, why not both. If you look at the example circuits from LM3915 datasheet, page 18 - Figure 28, you will see an example of combining two ICs. There are plenty designs for this but this one combines LM3915 and LM3916 as an Extended range VU meter. With this you can see bigger portion of audio signal for bigger clarity. It only uses 4 external resistors and one trimmer to adjust it to show values precise. You don’t need to worry about that power supply with transformer. If you look at it, It’s rectifying as voltage for + peaks and smoothing it out. And judging form a small 2.2uF capacitor, this circuit doesn’t have a big current consumption. You can Forget that part and just use any supply that doesn’t have much filtering, as the datasheet suggest. You can use the same one for ICs and for LED as they have common GND but I will be testing both to compare.

This is it for the part, now go to the next step to see the schematic and what parts do you need.

Step 2: TOOLS

You are going to need just a few basic tools for electronics.

· Soldering iron

· Solder

· Pliers

· Hack saw / Dremel

· Electrical tape

· Optional 1,2mm and 1,7mm drill bit for larger leaded parts

Step 3: SCHEMATIC

So, now that I’ve chosen the circuit that I’m going to work with, I am
going to show you some improvements that I have come across from building the prototype. So before I give you a list of parts, here is the new schematic.

The new schematic includes some additional parts that improve the operation of VU meter.

Our IC’s output to LEDs around 1.28V and around 10mA. And if we multiply that by 19 we get, that all of our LEDs draw 0,24W of power. And let’s say that depending on the song or sound, that you are listening to, all of the LEDs might turn to full power at once.

Therefore, you need to assure that the input voltage to the IC doesn’t drop to much or at all or it might corrupt the operation. No, it’s not bad but when we were working on our VU meters with other equipment and filters, they weren’t responding good when a loud sound was sent to them. Therefore, they weren’t responding or flashing so it appeared as they weren’t working.

So we need to add in a big capacitor on the input to assure that it stores energy while your power supply adjusts its voltage in order to supply enough current à power. In order to give a minimal capacity, you can calculate amount of power that this circuit needs to operate in the meantime. We could calculate a minimal value capacitance, but you can just use a correct voltage specified capacitor with a capacity of 1000uF – 2000uF and it should be enough.

I also added a way to power it. I had one female USB B type connector on hand and it’s one of my favorite as they are robust and I have quite some cable running around from Arduinos. Search for the pinout to determent which pin is power and which one is ground. I also added an audio jack. You can use a stereo and use just 2 resistors to combine stereo audio into one or you will have only one channel on your VU meter or you can build 2 VU meters, one for each channel L and R.

Step 4: PARTS

So, here is a list of all components.

- IC1 = LM3915

- IC2 = LM3916

- USB-1 = USB type B connector

- R1, R4 = 1kΩ, ¼W

- R2 = 5,11kΩ, ¼W

- R3 = 500Ω potentiometer / trimmer

- R5 = 750Ω, ¼W

- R6 = 100kΩ

- R7, R8 = 10kΩ

- R9 = 20kΩ

- R10 = 200Ω

- R11 = 100kΩ potentiometer / trimmer

- JACK-1 = stereo audio jack 3.5mm

- C1 = +1000uF electrolytic capacitor

- LED 1 = 5mm LED

Step 5: BUILD

For the build, there are just a few steps.

- Make the main circuit on a board

- Power the board without ICs in their sockets and check voltages at those pins where it should be power supply, ground, signal …

- Insert ICs and check currents that supply the board to see that the board doesn’t draw too much

- Make sure nothing gets hot or more than reasonably warm as without LEDs, everything should stay cold.

- Make strips of pcb to solder LEDs on; you might have to stich 2 parts of a board as only really big pcbs are capable of holding 19 – 20 8mm LEDs

-I made molex connectors from board to LEDs with ribbon cable as I want the LEDs to be detachable from the main board.

- Connect everything up with your favorite tunes or in my case, I used a test 1kHz sine wave

Now that you have everything working, you can clean your pcb with some isopropyl alcohol to clean flux resin that is left over from soldering.

Now you can watch a video that I made so you can build your VU meter as you watch the video. I intended to make this instructable only in video, but I decided that the video will include the whole build and testing process and in this instructable I described all details. I hope you like it as a lot of time was put into it.

Step 6: Conclusion

So, what was the purpose of this instructable. I can honestly say, that this isn’t the best VU meter that you can build. Well, it’s one way of doing it with, which is with dedicated ICs. And There are a number of things that could be improved. There can be an OP-AMP in the input to compensate for different input signals as some appliances have higher output voltage than others; like a smartphone or my big amplifier tower. I could add channel mixing, so my VU meter could display both channels of audio. I could also ditch these dedicated IC’s and could have used MANY op-amps for each LED or two and separate each LED level with a different voltage threshold in audio intensity.

Yes, but what I also wanted to prove is that you can take an IC, go to its datasheet, test around and make it work. That datasheets are very useful and can be very helpful apart from just looking up voltage power ratings. I hope you enjoyed this instructable, maybe you learned something new and as always, I’ll see you in the next instructable :)