Principle of Breathing Effect Control for Automotive Electronic Ambient Lighting

In the fiercely competitive automotive industry, car manufacturers devote significant efforts to features that users can perceive instantly. For a vehicle, its appearance is the initial impression for users.

Once users are captivated by the vehicle's design at first glance, in order to persuade them to purchase the car, the interior cabin design becomes crucial. 

If we compare the vehicle's exterior to its outward appearance, the cabin can be seen as its inner soul. An interesting interior soul can stand out from a sea of ordinary exteriors.

Apart from well-known elements like sofas, televisions, and large refrigerators, there are also some less noticeable designs within the cabin, such as today's protagonist—the ambient lighting.

Ambient lighting has been around for many years, starting from single-color ambient lighting and progressing to 64-color, 128-color, and now 256-color ambient lighting, making its functionality increasingly powerful.

Introduction to RGB

RGB color mode is an industry-standard color model that utilizes variations in the Red (R), Green (G), and Blue (B) color channels, as well as their combinations, to produce a wide range of colors. 

This color standard encompasses almost all colors perceptible to the human eye and is one of the most widely used color systems.

In computers, the "amount" of RGB refers to the brightness and is represented using integers. Typically, each RGB channel has 256 levels of brightness, represented numerically from 0 to 255. 

Based on calculations, the 256-level RGB color model can produce approximately 16.8 million colors, which is equal to 256 × 256 × 256 = 16,777,216. This is commonly referred to as "16 million colors" or "24-bit color" (2 to the power of 24).

RGB is designed based on the principle of color emission. 

In simple terms, its color mixing method is similar to having three lights—red, green, and blue. When their lights overlap, colors blend while the brightness equals the sum of the individual brightness values. 

The more they mix, the brighter the resulting color, known as additive mixing. The brightest overlapping region of the three primary colors is white. The characteristic of additive mixing is that the more colors overlap, the brighter the result becomes.

Principle of Ambient Light Control

An ambient light, or mood, lamp is essentially composed of small LED lights. In its simplest form, a monochrome ambient light can be achieved using regular LEDs. 

However, for multi-color ambient lights, RGB (Red, Green, Blue) LEDs are used. The ambient light creates different colors by controlling the proportions of RGB.

Users set different values for the RGB components to generate various colors and adjust the brightness of the ambient light. 

These corresponding RGB values and brightness are input to the LED driver chip. 

After the driver chip decodes the input, it controls the pulse-width modulation (PWM) duty cycle of the RGB LED lights, thereby controlling the color and brightness of the ambient light.

The control of RGB LED brightness and color essentially involves adjusting the PWM duty cycle for each RGB channel, which in turn controls the current flowing through the LEDs to achieve the desired color and brightness. 

The PWM frequency needs to be higher than the discernible frequency by the human eye to prevent flickering of the lights.

Control of Breathing Effect for Ambient Light

To achieve the breathing effect in the ambient light, we can control the light to gradually increase and decrease in brightness. 

Let's consider a breathing frequency of 1 second and a brightness cycle from the brightest to 30% brightness. 

By uniformly decreasing the PWM from 100% to 30% within 1 second and then uniformly increasing it back to 100%, we can create the desired breathing effect. 

The breathing frequency and brightness cycle can be adjusted according to the desired experience.

Ambient Light Music Rhythm Control

To control ambient lighting in sync with music, we can extract the musical notes from the music score and translate them into different frequencies. 

Typically, all the notes are converted into three different frequency ranges: high, medium, and low. Since each note has a different duration, by considering the different frequencies and their respective durations, we can create varying rhythms and patterns in the ambient lighting to match the music. 

This allows the ambient light to dynamically respond to the changes in the music, enhancing the overall audio-visual experience.

For instance, when the music has a low frequency, the ambient light can be set to color E, while it can be set to color F for medium frequency, and color G for high frequency. 

Alternatively, when the music has a low frequency, the ambient light can be set to color H, color I for medium frequency, and color J for high frequency. Additionally, both the color and brightness of the ambient light can change simultaneously based on different music frequencies. These settings can be adjusted according to the desired user experience.

The above examples serve as an introduction, and the design possibilities for ambient lighting can be further expanded. 

As an integral part of the cabin ambiance, the ambient lighting can even change colors to reflect the driver's mood.

It is worth noting that the current ambient lighting systems consist of multiple LED modules, ranging from 5 to 30 LEDs or even more. This means that the ambient lighting can create more elaborate combinations. 

Each LED can be individually controlled for color and brightness, providing designers with ample opportunities to deliver advanced visual experiences to users.

Ambient lighting system solution introduction

Currently, ambient lighting systems primarily use LIN (Local Interconnect Network) or CAN (Controller Area Network) communication protocols. 

LIN is a popular and cost-effective solution, widely used in the market. However, with a sufficient budget, CAN becomes a superior choice as it offers higher bandwidth and supports Over-the-Air (OTA) upgrades.

LIN communication frames are limited to 8 bytes (64 bits) per message. In most cases, an ambient light strip consists of multiple LEDs. 

If individual control of each LED's color and brightness is desired, it requires 24 bits for color (8 bits per RGB component) and 7 bits for brightness (with 1% precision).

Thus, each LED requires a total of 31 bits. Considering 4 bytes per frame, a single LIN frame can only control 2 LEDs individually. 

Therefore, LIN-based ambient lighting systems usually utilize the available bandwidth to achieve various control effects. Unless the control requirements are exceptionally complex, LIN solutions are generally sufficient for ambient lighting applications.

On the other hand, a CAN-FD (Flexible Data Rate) solution allows for sending frames of up to 64 bytes. 

This enables individual control of up to 16 LEDs in a single frame, meeting the needs of most ambient lighting scenarios. 

With this enhanced hardware capability, more diverse lighting effects can be achieved. While it may come at a higher cost, the advantages outweigh the drawbacks.

As automotive development progresses towards the era of intelligence, people's expectations are also increasing. 

Vehicles should not only have a stylish appearance but also keep up with interior advancements. Ambient lighting is destined to become a standard feature, as it enhances the overall ambiance of the vehicle.