LED Volume Tower
Music Responsive LEDs to Any Sound SystemBy Ben Finio
Assembly Time: 4 hours
Build a Mini Stereo LED Tower, also known as a VU meter, that lights up 10 LEDs proportionally to the volume of an analog audio signal. This is a super cool way to add music responsive LEDs to a sound system.
It will work with any system that has a 3.5mm audio jack. As a beginners kit you will only need basic soldering skills. Access to a 3D printer and laser cutter is only necessary if you want to make your towers exactly as pictured. I have provided the CAD files below if in case, however, you could easily build them using another medium, such as wood.
Required tools and components:
LM3914N-1 LED Driver
T1-3/4 Green LED
T1-3/4 Yellow LED
T-1 3/4 Red LED
T1-3/4 Orange LED
T1-3/4 Blue LED
Stereo 3.5mm Male Plug to 3.5mm Male Plug 6 Ft Cable
6" Y 3.5mm Male Plug To 2x3.5mm Female Jacks
LM3914N-1 LED Driver 10-Segment 18-Pin MDIP Rail
Battery Holder 3-AA Wires With Cover and Switch
400-Point Solderless Breadboard 3.3"Lx2.1"W
Battery Alkaline AA 1.5V
Single Turn 3/8" Square Cermet 10k Pot
70-Piece Jumper Wire Kit
0.3A 125V AC SPDT on-on Slide Switch
Stranded Hook-Up Wire - Black
Acrylic sheets (optional)
3D printed Towers (optional)
Here's a quick video of the build.
Step 1: Prototyping the circuit on a breadboardCut off one end of your 3.5mm audio cable and strip and tin the ends of the three wires inside (ground, left and right audio). Follow the diagram and assemble the circuit on the breadboard. Be sure to keep the battery pack OFF to prevent accidental damage if in case the wiring is incorrect.
Plug the audio splitter cable into your audio source and plug your external speakers into one jack, and the 3.5 mm cable connected to your breadboard into the other.
Step 2: Circuit diagramHere's a regular circuit diagram for half of the circuit. Each half of the circuit is identical, the only difference is whether they're connected to the left or right audio channel.
Step 3: Testing your circuitDouble check the wiring to make sure everything is connected properly. Turn the battery pack ON and play a song from your audio source. Watch the LEDs, they should light up when louder sounds play. At this point you may need to make a few adjustments.
The potentiometers adjust the reference voltage for each LED driver. If your LEDs aren't lighting up at all or are always lit you will want to slowly adjust the potentiometers until you receive a good response.
The switch toggles the drivers between "bar mode" and "dot mode". Use whichever one you like best. So that the music doesn't get painfully loud, external speakers with their own volume control that can be adjusted independently, work best.
I do not have the 3.5mm audio cable connected in the circuit above. Instead, I added a third 10k potentiometer set up as a voltage divider, to use as an input instead of the audio signal. The third potentiometer is just for testing purposes, so is not included in the kit.
Step 4: Building the towersI designed 3D printed towers with 10 slots to hold LEDs and acrylic sheet diffusers. If you have access to a 3D printer and laser cutter, you can download the CAD files using the link below:
If you don't have access to these tools, you could drill holes in a piece of wood and paint it or use another medium.
Step 5: Connecting the LEDsThe leads of the LEDs fit through tiny holes in the tower. You can use a SMALL dab of hot glue to hold them in place. Make sure you glue from the back, you don't want the glue visible from the front. Pop the acrylic sheets in over the LEDs.
Step 6: SolderingThe LEDs in the circuit all share a common anode (the longer lead). Solder together the longer leads for the LEDs on each tower. Then solder individual segments of hookup wire to the cathode for each LED. Strip and tin the other ends of the wires and connect them to the circuit as shown back in step 1.
Only one color of hookup wire is included in this kit, so pay attention to which wire is connected to which LED, or the LEDs will light up all out of order.
Step 7: Enjoy and get the part startedAs long as you soldered the LEDs and connected them to the breadboard properly, the circuit should function exactly the same. Try playing another song and make sure your towers still work. With 22 wires coming from the LEDs, odds are that a few might have been mixed up, so be sure to double check. Adjust the potentiometers as needed, then sit back and enjoy the light show!
Ben Finio is a mechanical engineer/roboticist turned informal science educator. For his day job he writes K-12 science and engineering projects for the STEM education nonprofit Science Buddies (www.sciencebuddies.org). In his spare time he likes to write Instructables, usually about things like robots, Arduino, and Raspberry Pi.