Basic components for building mHealth devices.

One step beyond the platform is adding other components. What do you create when your motto is “Computing stuff tied to the physical world?”  A tiny, fairly well featured kit with wireless capability. The JeeNode wireless communication platform.

It looks like a fun and cost effective way to get into experimenting with RF communication. By combining an Arduino-compatible processor (ATmega328) with a low-cost HopeRF radio module, Jean-Claude Wippler in a town called Houten, The Netherlands,  creates these building blocks and offering them for sale as a kit, or, since it is an open source hardware design, you can just download the PCB layout and roll your own. You can think of lots of applications (remote candle lighter, interactive cat toy:)) that aren’t worth a full xBee-based solution, where it would be handy to have a development board like this that I could just drop in and use.

Jee Labs also has a weblog with daily news about projects being worked on in the fascinating world of physical computing, wireless comm’s, sensors, lights, switches, motors, robots, WSN’s, Arduino’s, you name it.

Building a sensornetwork for mHealth purposes.

For a wireless sensor network you need a platform to start with. But what? Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It’s intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.

Arduino can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on the board is programmed using the Arduino programming language (based on Wiring) and the Arduino development environment (based on Processing). Arduino projects can be stand-alone or they can communicate with software on running on a computer (e.g. Flash, Processing, MaxMSP).

The boards can be built by hand or purchased preassembled. The software can be downloaded for free. The hardware reference designs (CAD files) are available under an open-source license, you are free to adapt them to your needs.

Wireless Sensor Networks and mHealth basics 3.

Last theory on Wireless Sensor Networks coming up. What about the software, middleware and programming languages?

Software

Energy is the scarcest resource of WSN nodes, and it determines the lifetime of WSNs. WSNs are meant to be deployed in large numbers in various environments, including remote and hostile regions, with ad-hoc communications as key. For this reason, algorithms and protocols need to address the following issues:

• Lifetime maximization
• Robustness and fault tolerance
• Self-configuration

Middleware

There is considerable research effort currently invested in the design of middleware for WSN’s. In general approaches can be classified into distributed database, mobile agents, and event-based.

Programming languages

Programming the sensor nodes is difficult when compared with normal computer systems. The resource constrained nature of these nodes gives rise to new programming models although most nodes are currently programmed in C.

• c@t (Computation at a point in space (@) Time)
• DCL (Distributed Compositional Language)
• galsC
• LabVIEW
• nesC
• Protothreads
• SNACK
• SNAPpy (Python)
• SQTL
• Java Sun SPOT
• uSWN

Wireless Sensor Networks and mHealth basics 2.

What standards, hardware and operating systems are  used for wireless sensor networks? There are three. I wrote some articles about ZigBee. It´s a proprietary mesh-networking specification intended for uses such as embedded sensing, medical data collection and home automation. WirelessHART is specifically designed for Industrial applications. 6LoWPAN is the IETF standards track specification. Also relevant to sensor networks is the emerging IEEE 1451 which attempts to create standards for the smart sensor market. The main point of smart sensors is to move the processing intelligence closer to the sensing device.

Hardware

The main challenge is to produce low cost and tiny sensor nodes. With respect to these objectives, current sensor nodes are mainly prototypes. Miniaturization and low cost are understood to follow from recent and future progress. Some of the existing sensor nodes are given below. Some of the nodes are still in research stage. Also inherent to sensor network adoption is the availability of a very low power method for acquiring sensor data wirelessly.

Operating systems

Operating systems for wireless sensor network nodes are typically less complex than general-purpose operating systems both because of the special requirements of sensor network applications and because of the resource constraints in sensor network hardware platforms. Wireless sensor network hardware is not different from traditional embedded systems and it is therefore possible to use embedded operating systems such as eCos or uC/OS for sensor networks. However, such operating systems are often designed with real-time properties. Unlike traditional embedded operating systems, however, operating systems specifically targeting sensor networks often do not have real-time support.

TinyOS is perhaps the first operating system specifically designed for wireless sensor networks. Unlike most other operating systems, TinyOS is based on an event-driven programming model instead of multithreading. TinyOS programs are composed into event handlers and tasks with run to completion-semantics. When an external event occurs, such as an incoming data packet or a sensor reading, TinyOS calls the appropriate event handler to handle the event. Event handlers can post tasks that are scheduled by the TinyOS kernel some time later. Both the TinyOS system and programs written for TinyOS are written in a special programming language called nesC which is an extension to the C programming language.

There are also operating systems that allow programming in C. Examples of such operating systems include Contiki, MANTIS, BTnut, SOS and Nano-RK. LiteOS is a newly developed OS for wireless sensor networks, which provides UNIX like abstraction and support for C programming language.

Wireless Sensor Networks and mHealth basics 1.

Building a Wireless Sensor Network is fine, but what are the unique characteristics of such a network:

• Limited power they can harvest or store
• Ability to withstand harsh environmental conditions
• Ability to cope with node failures
• Mobility of nodes
• Dynamic network topology
• Communication failures
• Heterogeneity of nodes
• Large scale of deployment
• Unattended operation
• Node capacity is scalable,only limited by bandwidth of gateway node.

Sensor nodes can be imagined as small computers, extremely basic in terms of their interfaces and their components. They usually consist of a processing unit with limited computational power and limited memory, sensors (including specific conditioning circuitry), a communication device (usually radio transceivers or alternatively optical), and a power source usually in the form of a battery. Other possible inclusions are energy harvesting modules, secondary ASICs, and possibly secondary communication devices (e.g. RS-232 or USB).

The base stations are one or more distinguished components of the WSN with much more computational, energy and communication resources. They act as a gateway between sensor nodes and the end user.