When EnOcean brought the first generation of battery-less radio modules to the market, most of their unique features – such as a 20 nA wake-up timer – had to be built in complex discrete analog electronic circuits. In recent years, EnOcean has developed the Dolphin chip integrating ultra-low power radio with an energy harvester interface and a microcontroller.
These self-powered devices are connected via a wireless network or via USB links to a central gateway. This gateway can be powered by the Linux operating system to provide the central coordination and control. This is a key element of building a self-powered network for home or industrial automation.
The TCM 300 module is aimed at line powered actuators, repeaters and gateways and the STM300 is designed for use in energy harvester driven sensors and actuators.
Figure 1: The STM300 low power module from EnOcean for a network powered by energy harvesting.
The TCM transceiver modules allow line powered actuators, repeaters, and gateways to be built. The module provides several built-in operating modes for serial communication, or switching and dimming of output loads. In addition, repeater functionality (1 or 2 level) can be activated. The TCM 300 and TCM 320 offer two different mounting options. TCM 300 can be mounted as an SMD component on a host PCB while the TCM 320 is designed for vertical mounting using a pin connector.
The power saving RF transmitter module, the STM300 from EnOcean, enables wireless and maintenance-free sensors and actuators such as room operating panels, motion sensors or valve actuators for heating control. Power is provided by an external energy harvester such as a small solar cell or a thermal harvester that uses the Peltier effect. An energy storage device can be connected externally to bridge periods with no supply from the energy harvester. A voltage limiter avoids damaging the module when the supply from the energy harvester gets too high.
The module provides a user configurable cyclic wake up. After wake up, a radio telegram (input data, unique 32-bit sensor ID, checksum) will be transmitted in case of a change of any digital input value compared to the last sending or in case of a significant change of measured analog values (different input sensitivities can be selected).
In case of no relevant input change, a redundant retransmission signal is sent after a user-configurable number of wake-ups to announce all current values. In addition, a wake up can be triggered externally.
This can include wall-mounted flat rocker switches with 1 or 2 rockers, as well as handheld remote controls with up to four single pushbuttons that are powered by the action of pressing the switch.
In the PTM200C rocker switch, a common electro-dynamic energy transducer is actuated by a bow, which can be pushed from outside the module on the left or right by an appropriate pushbutton or switch rocker. When the energy bow is pushed down, electrical energy is created and an RF telegram is transmitted including a 32-bit module ID. Releasing the energy bow generates different telegram data, so every PTM telegram contains the information that the bow was pressed or released. In addition, the radio telegram transmits the operating status of four contact nipples when activating the bow. This enables the identification of up to two appropriate switch rockers or up to four single pushbuttons.
Figure 2: The EnOcean modular architecture.
The new hardware platform is capable of bidirectional communication. This is made possible by the integrated EnOcean transceiver chip that provides energy consumption down to 220 nA, programmable transmit power up to 6 dBm, and a digital state engine that ensures energy saving handling of transmit and receive operations while at the same time taking considerable load off the integrated 8051 controller. Of course there is full compatibility with existing wireless EnOcean products.
The Dolphin platform
The built-in firmware in the Dolphin platform allows simple integration. In addition, an application-programming interface (API) allows the OEM to take full advantage of the capabilities of the modules.
Through the built-in application functions, Dolphin modules enable straightforward start-up and system integration. The operating modes can be configured simply by a few external components (voltage dividers or 0 Ω bridges). The EDK300 development kit supports evaluation of all operating modes and configuration options and can be used as a starting point for the development of your own firmware.
Figure 3: The EDK 300 development environment.
The Dolphin sensor module includes the complete RF circuitry and provides outputs for a whip antenna or an external 50 Ω antenna, so there is no need for RF expertise on the OEM side. A radio certification for the modules is available for use with several antenna options. If these are used, a radio approval for the end device is not required, saving the OEM a lot of effort and money for external approval cost.
Many configuration options are available for the built-in firmware. These allow off-the-shelf modules to be used in a wide range of applications such as gateways, repeaters, actuators, or uni- and bidirectional sensors.
Figure 4: The Dolphin sensor module.
If this is not sufficient, more complex or completely different applications can be built using the API. Despite using an 8051 controller, detailed microcontroller expertise is not required. Programming is in the high level C language. All the resources of the integrated Dolphin chip are made available, including up to 16 digital or analog I/Os, the RF transceiver, an 8051 microcontroller with 32 kB Flash and 2 kB RAM, several timers and ultra-low power management functions.
Using the API, it is possible to develop bidirectional self-powered sensors and actuators using the new SMART ACK technology. By switching its receiver on for only a few milliseconds after transmitting a telegram, a self-powered sensor can receive an answer from a line-powered counterpart, which, for example, may contain data to show on its display.
The powerful development environment that comes with the API ensures fast development times. Dolphin Studio serves for configuring different API modules and makes laborious study of register settings obsolete. The resulting configuration file is simply included in the C program. The documented source code of TCM 3x0 and STM300 is provided for training purposes and as a base for fast customer specific adaptation.
The high degree of integration means repeater functionality can now be activated on every actuator, as every node is bidirectional. In most cases this will save the cost for a dedicated repeater device in an installation. The microcontroller on board the Dolphin modules can now also be used to perform application specific tasks. The cost for an additional external microcontroller – which has been used in many applications in the past – can be saved.
The STM300 and TCM 300 are now designed as SMD components and are delivered on Digi-Reel. They can be handled in production in the same way as any other SMD component, e.g. a microcontroller. This allows fully automated production whereas the previous module generation always required costly manual steps. This will strongly reduce the OEM´s production cost and enhance the quality of the end device.
USB radio gateway
Using an FTDI USB to TTL Serial Cable and an EnOcean TCM 300 device, it is very easy to build a compact USB-based wireless device.
Drivers are available for Linux, allowing the control and monitoring applications on the development platform. This device works as a plug-and-play device also with the free EnOcean evaluation tools, WinEtel and Dolphin View, without the need for extra drivers.
For all the TCM devices, the first step is to ensure that the supply voltage rail is noise free. Additional capacitors, at least 22 μF Tantalum and 0.1 μF ceramic should be added to smooth out EMI added by the PC USB connector providing the voltage supply. Depending on the TCM device being used, the USB to serial Cable Type TTL-232R-3V3 header wires can be connected as shown Table 1.
All TCM 120 / 2x0C / 3x0(C): Pin 7 (In) -> TXD – Orange
All TCM 120 / 2x0C / 3x0(C): Pin 8 (Out) -> RXD – Yellow
All TCM 120 / 2x0C / 3x0(C): Pins 1, 16 (GND) –> GND - Black
Note: The Green and Brown wires (Handshake signals) are thereby not used, (NC).
Table 1: Wire allocations for the FTDI USB interface.
The FTDI USB converter supply voltage (the red wire) delivers +5 V for other TCM devices, but the TCM 300 family requires a +3 V supply voltage. This means an additional linear 3 V LDO regulator must be used in series between the Red +5 V output and Pin 15 (VCC/VDD=3 V). All the FTDI devices are now supported in Ubuntu 11.10, kernel 3.0.0-19.
To link up the gateway, the first thing to do is install the libraries that allow Linux to read the sensors. This is done by installing the lm-sensors library [sudo apt-get install lm-sensors].
In Ubuntu, the install will ask several questions. First it will ask if it should run SUID root, select “yes”. It will then ask you for an interval for logging the sensor data, usually a value between 2 and 10 seconds. The sensor data acquisition routine should then be run as a daemon on startup, leaving the default values for hostname and port.
In Ubuntu, the [sudo sensors-detect] command will probe the system for sensors. This will scan the system, giving a summary of the sensors available to the gateway. The modules to support the sensors can then be automatically loaded on startup so that they are available on reboot.
Without a reboot, the code modules are loaded with the modprobe command [sudo modprobe [module name]] for the devices detected and listed.
Running [sensors] as a command will then output the data from the sensors that are loaded. A graphical applet for the Gnome desktop can be used to display the data. The command [sudo apt-get install sensors-applet] will provide the applet that can be added to the desktop or third party display if required.
Of course the Dolphin development environment provides a wider range of capabilities to develop more complex solutions across a wide range of EnOcean energy harvesting sensors and actuators. This can be done easily through the TCM-Monitor tool in the development environment to set the COM port for the appropriate USB link.
In addition to the protocol stack for EnOcean wireless, the API offers many powerful functions, for controlling energy management for example, use of digital or analog I/Os, access to flash memory and the continuously powered RAM0, and control of timer functions.
EnOcean has added the powerful Dolphin Studio development environment to the API. This supports configuration of the various API modules and ensures fast time to develop. The command line program integrated in Dolphin Studio controls the programming operation, and it is easily implemented in fabrication and T&M engineering.
The API provides the interface to the hardware, pulling together all the relevant libraries for both the wired and wireless energy harvesting sensors and actuators. This handles the radio interfaces, linking the physical hardware through the data link and network layers, as well as providing the RF configuration, routing and ID management for the wireless devices. The API also handles the encryption, power management, I/O, UART and memory access for the microcontroller as well as configuring the timers.
Figure 5: The Dolphin software API architecture.
All this provides a high level interface for developing complex software for a Linux gateway. The code can be assembled from the API libraries and compiled with a mainstream compiler to run in the Linux environment, giving the developer flexibility for different platforms, all based around the EnOcean energy harvesting sensors and actuators.
This allows a wide range of OEMs to develop their own gateway devices using the Dolphin API and Linux operating system to create a complex, reliable automation network using energy harvesting.
