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Project Notes

#212 StayCreative

Audio level VU meter driving a custom LED sign.

Here’s a quick video of it in action:



A simple project inspired by Make your own LED Sign VU Meter by GreatScott!. The catch-phrase should be familiar if you subscribe to his channel;-)

It’s a VU meter, but rather than doing the “bar graph” thing à la LM3915, it pulses the intensity of all LEDs to the volume of the incoming audio.

Audio Input

Consists of a standard electret biasing ciruit. The AC signal via 1µF ceramic feeds through an adjustable passive attenuator (22kΩ | 100kΩ pot) to the amplifier stage.

The audio signal is amplified with an LM358 in non-inverting amplifier configuration with a hefty 330x gain. This means I can get good dynamic range even with weak input signals.

LED power supply

Power for the LEDs is provided with a simple buck converter module dialed in at ~3V, which is around the nominal forward voltage of the blue LEDs I’m using.

LED brightness control is enabled with an n-channel MOSFET on the common cathode connection of the LEDs. At first I though I might need some serious juice, and was going to use an IRF540N which can handle many amps. But it turns out that the current draw is about 50mA with all the LEDs fully on so I ended up using a 2N7000 instead.



The Schematic

The Build


Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.