Digital lighting enables precise, individual control of the brightness and color of a light source. These light sources are particularly interesting in applications that enable dynamic color effects. This requires anywhere from dozens to hundreds of light sources. The lead image illustrates how this technology can be used to create digital lighting effects in the side doors of a vehicle.
To keep these applications as compact as possible while enabling dynamic light adjustment, these light sources are best controlled intelligently through a suitable protocol. The protocol must deliver high-level color accuracy and update rates while optimizing resource efficiency.
From RGB to OSP
Light colors are typically created by mixing the three primary colors: red, green and blue (RGB). Given the typical color accuracy requirements in the automotive industry (u’v’ < 0.01), each primary color requires a resolution of approximately 16 bits. This results in a usable data volume of 3 x 16 bits per light source.
The light sources’ update rate should match that of a quality display of around 100 Hz or 10 ms. The protocol should be designed for compact integration within the light source, i.e. to occupy the smallest possible space at the lowest possible cost. The goal was to integrate it into an RGB LED – an LED containing three chips in the primary colors: red, green and blue. With these considerations in mind, a protocol was defined and published as the Open System Protocol, or OSP for short.
OSP allows a microcontroller (µC) to control a chain of light sources bidirectionally or in a ring configuration. Figure 1 shows a possible physical arrangement of the µC and the light sources, here generally called nodes. Electrical data transfer between the nodes can take place via LVDS or CAN FD (physical layer). The transmission rate is 2.4 MHz, and the data is Manchester encoded.
True to its name, the Open System Protocol is an open protocol that allows developers to create their own applications without license fees. Standardization of the protocol has just been initiated.
OSP also meets the aforementioned update frequency and color accuracy requirements for strips or areas containing up to 200 RGB LEDs equipped with this intelligence. This would enable implementations like door paneling. Any patterns or real images could be displayed in real time. In principle, OSP allows up to 1,000 nodes to be addressed and controlled with up to 64 bytes of user data per telegram.
Microcontrollers for controlling OSP networks
OSP has already been implemented, resulting in two components: An intelligent RGB LED and a smart stand-alone driver. These two elements can be connected to each other within an OSP network. Usually, this network is controlled by a microcontroller or a gateway controller. To do so, it must have also implemented the OSP protocol or the OSP protocol stack. A number of controllers with this OSP protocol stack are already available, for example controllers from Infineon (Traveo T2G, PSoC) and other MCU suppliers, as well as Arduino-based boards such as the Rutronik Development Kit RDK4 and the current adapter board RAB5 - OSIRE (see box text) for quick and easy commissioning.
Suggestion for info box:
Advanced LED solutions: With OSIRE® LEDs from ams OSRAM
Leverage the Rutronik adapter board RAB5 - OSIRE to develop applications for interior and ambient lighting, as well as RGB control elements. The versatile approach of Rutronik System Solutions unlocks a world of further possibilities thanks to the Arduino interface, which enables multiple boards to be stacked.
The RAB5 contains OSIRE® LEDs from ams OSRAM as a key component. The LEDs are designed for dynamic ambient lighting and feature individually addressable chips for maximum flexibility in color and driver selection. Additionally, ams OSRAM’s intuitive GUI enables easy programming of each individual LED, thus improving usability and customization options.
The combination of the adapter board RAB5 with the base board RDK4 is particularly effective thanks to the automotive-qualified microcontroller integrated on the RDK4. More specifically, Infineon’s PSOCTM 4100S Max, with its cost-effective Arm® Cortex®-M0+ automotive microcontroller, enhances this setup with seamless integration and advanced control capabilities.
OSP now offers a protocol that, in accordance with its basic requirements, enables high-speed downstream data transfer from a controller to the connected OSP nodes. Moreover, OSP also allows the controller to retrieve data from the network. This can serve diagnostic purposes; however, the controller can generally also read data from the network. Furthermore, OSP does not specify the type of nodes in the network. It only knows data, not content. Other node types – such as actuators or sensors – can therefore be integrated into a network and controlled via the controller alongside the light sources. This results in a network capable of performing tasks and functions beyond simple light display.
In order to be recognized and controlled within the OSP network, OSP must be integrated into each node. Alternatively, a device that is not OSP capable can be integrated into the OSP network via a small gateway. The aforementioned smart stand-alone driver offers precisely this function as an OSP-to-I2C gateway. This allows actuators and sensors to be integrated into the OSP network via their I2C interface.
Additional sensors and actuators have already been incorporated into lighting applications in early prototypes. All functions are enabled via one and the same OSP network.
Digital lighting and more
The term “more” refers exclusively to functionality: OSP allows more than simple lighting control and offers an expanded range of applications. While OSP was designed specifically for automotive use, it is equally applicable to other applications. OSP is open to all and allows for the addition of further and specially developed functions. Therefore, OSP can be used and expanded by any developer. To highlight this openness, ams OSRAM has released an OSP software package for Arduino on GitHub. The software provided is freely accessible.
For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.
Subscribe to our newsletter and stay updated.