Beginning in 1990, control networks began the transformation of automation systems from direct digital controls to true networks. Unlike data networks that connect our PCs and servers, control networks connect machines (or devices) to other machines, forming automation systems for our homes, buildings and factories. A decade and a half later, nearly every industry has adopted standards or de facto standards for control networking. The benefits for networked controls have been many, but they chiefly result in lower installed costs, lower life-cycle costs, improved system management and diagnostics, and lower energy consumption.

Subcomponents with Pyxos ICs can create an internal embedded control network within an application, such as a refrigerator or photocopy machine.

However, while the industry has grown tremendously for control networking, a vast market for controls has remained largely untouched ­ the market for embedded control networks.

Advances in silicon design combined with key capabilities of control networks has created the opportunity for a new market beyond networking machines ­ the networking of the multitude of sensors and actuators embedded inside of these machines. Consider a washing machine for instance, where inside there are moisture sensors, valves, heat sensors, flow sensors, small motors, door sensors, leak sensors, a large motor, and more. Most machines connect all these pieces to a controller of some sort via a thick wiring harness comprised of a pair of wires for each sensor or actuator. This wiring method inherently introduces errors in the assembly process, contributes to field failures of the harness, and adds parts costs in the form of multiple connectors and wiring. In fact, in some industries, faulty wiring and failure of the RS-485 connections contribute over 40 percent of the overall warranty costs.

Improved reliability; simpler, more flexible, lower cost assembly; reduced weight and materials; improved performance; and enhanced functionality are the potential benefits designers can achieve by adopting embedded control networks inside of machines to replace existing wiring and bus technologies.

The small size of Pyxos chips makes it easy to embed them in a wide variety of components.

The primary requirements for a successful embedded networking solution are:

• Easy installation.
• Reduced wiring costs.
• High reliability.
• Deterministic communications.

To provide such a solution, Echelon Corp. developed the Pyxos embedded control networking platform. The system consists of Pyxos Points embedded inside sensors and actuators, and Pyxos Pilots that act as controllers for the network and can be designed to connect the machine to a control network. While designed for both wired and wireless communications, the first iteration of Pyxos is wired for suitability inside machines as well as to support harsh environments where RF is not suitable.

Architecture and components

Pyxos Embedded Networks: A Pyxos network consists of up to 32 Pyxos Points embedded in sensors and actuators and a Pyxos Pilot to manage network traffic and control. Pilots may also act as interfaces to control networks and the Internet. The network protocol operates at 312 kbps using a time-division multiplexing algorithm (TDMA). A fully loaded, 32-node Pyxos network has deterministic performance of 25 ms. Reducing the number of points results in higher performance as fewer points decrease the scanning loop time ­ a two-point network would only need 1.6 ms for a complete scan.

For closed-loop process applications, as well as sensing and control applications that require fast response time, designers can use a Pyxos network to replace the RS-485 bus, LIN or CAN bus.

Pyxos Points: The Pyxos FT IC is 5 mm x 5 mm and supports digital I/O directly. Alternatively, the chip’s serial peripheral interface (SPI) port can be interfaced with standard, low-cost microcontrollers for more complex I/O requirements such as the Atmel Tiny. The Pyxos ICs send both power and data on a single pair of unshielded wire (link power) and use a free-topology wiring architecture to allow manufacturers to wire components together in the topology that best suits the physical environment, such as star, ring, etc. Link power eliminates the need for a dedicated pair of wires, contributing to both cost reductions in parts, allowing cost, size and complexity reductions in Point designs.

Examples of Pyxos Point and Pilot block diagrams.

Self-Configuration: Pyxos networks configure themselves, that is, they install without the need for a software tool. For networks that are entirely contained in a single machine, such as a washing machine, the devices declare themselves and acquire unique network addresses upon power up. This scenario allows for extended flexibility in production lines without the need for additional or higher level training of line workers. For networks that are installed in the field, such as a small office space with a few sensors and a multi-function thermostat or room controller, Pyxos supports a push-button installation method.

Extending the platform

Pyxos networks can be integrated into LonWorks networks.

Machines with embedded Pyxos networks may be accessed remotely or interconnected using LonWorks® control networks. Designers may opt to include LonWorks connectivity in the Pilot to interconnect multiple Pyxos machines and/or to gain remote access to Pyxos machines over local or remote IP connections.

Within a self-contained Pyxos network, the Pilots and Points may be come from differing manufacturers who have embedded Pyxos ICs in their components or equipment. To achieve interoperability, the Pyxos platform leverages the interoperability methods and models used in LonWorks control networks and administered by LonMark International.

To provide common encoding of data values, each Pyxos network variable has a data type that is defined by a network variable type definition in a LonMark resource file. Pyxos Pilot manufacturers can provide specifications to the suppliers of Pyxos Points in the form of LonMark network variable type definitions for the Pyxos network variables that will be published and consumed by a Pyxos Point. To enable Pyxos Pilots and Pyxos Points from different manufacturers to interoperate, each type of Pyxos Point is identified by a standard program ID (SPID). The SPID is an 8-byte number within each Pyxos Point.

The format of a SPID is defined by the Pyxos FT protocol, which uniquely identifies the manufacturer, device class, usage, and model number for a Pyxos Point. The manufacturer of a Pyxos Point provides a Point Interface file for each of their standard program IDs. The PIF file defines the Pyxos network variables on the point in a standard format. A Pyxos Pilot can read this file to determine the Pyxos network variables published and consumed by a Pyxos Point.

When designers wish to incorporate Pyxos machines into larger environments, an interoperable connection must be built into the Pilot. The use of LonWorks transceivers in Pilots, coupled with application design that adhere to LonMark interoperability guidelines, enables installers and integrators of LonWorks networks to install and manage machines containing Pyxos networks as a standard LonWorks device using standard installation and management tools from a variety of vendors worldwide.

Designing out the standard bus and wiring harness in machines is an exciting prospect that can deliver lower cost, improved products, and a whole host of business benefits. Simple design tools, standard interfaces, and an existing ecosystem for extending the reach of the embedded control network will change fundamentally change machine design as well as the notion of what can be done with a network.