Servo Larson scanner

No LEDs Required For This Servo-Controlled Larson Scanner

All things considered, it’s pretty easy to get one LED is a strip to light up sequentially, and have it bounce back and forth. Turning that simple animation into a real Larson scanner, with smooth transitions and controlled fade-out, is another thing entirely. And forgetting the LEDs altogether and making a servo-operated Larson scanner is — well, let’s just call it an interesting lesson in hardware abstraction.

The Larson scanner, named after famed TV producer Glen A. Larson for his penchant for incorporating it into shows like Battlestar Galactica and Knight Rider, is actually hard to execute in hardware thanks to the fading tail that follows the lead pixel as it dances back and forth across the display. [Eric Gunnerson] decided to make this and other animation effects easier to achieve with Fade, a custom framework for LED animations that runs on an ESP32.

LED animations are fine, but what about servos? Could Fade be modified to support them? This turned out to be a fairly easy mod thanks to Fade’s architecture and [Eric]’s existing support for non-addressable LEDs via PWM signals. And it was even possible to support more than the 16 PWM channels on an ESP32by adding a UDP connection that puts multiple ESP32s under the control of a central microcontroller.

The video below shows [Eric]’s demo of servo support, with an eight-channel electromechanical Larson scanner. Each “pixel” is a painted ping pong ball swinging back and forth on a hobby servo, and the whole thing sounds just about as awful as you’d expect it to. If you squint just right, the effect looks pretty convincing, but that’s hardly the point. The real story here is [Eric]’s thoughtful architecture, which made the mods easier than starting from scratch.

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Dedicated LED Animation Framework For ESP32

[Eric Arcana] has been creating animated holiday decorations for several years, which involved a lot of custom code to make things light up the way he wanted, pulling the microcontroller to make changes. Using ESP32s with remote software updates is easier, but [Eric] also wanted to make the code simpler. To achieve this he created Fade, a custom programming language/framework for controlling LED animations from the ESP32.

Fade is written for addressable RGB LEDs like the Neopixel/WS2812. It keeps track of the current color of every LED in the system and allows the user to define what color it should be at a specified time in the future. Time is specified using 10 ms clock cycles. The LEDs will smoothly change from one color to the other in the specified number of clock cycles, without needing to specify what the intermediate colors should be.

Code is written in simple IDE, running on a web server on the ESP32 itself, or on a remote Windows PC. The language is very simple, but still powerful enough to create complex LED animations. A key part of it is the ability to specify multiple concurrent state changes in just a few lines of code. [Eric] also included optioning to take touch button inputs and use them to update the animations. Another nice feature is a simulation window on the desktop IDE. It allows you to create custom LED layouts on PC, and test your code without needing to send it to the ESP32.

Addressable LEDs have made creating large LED installations a lot simpler, like this 6 foot LED ball or a LED Video Wall.

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