Embedded Computing for Low Power Mobile Applications Introduction

L01 / Whit Smith

Solar Jackets Human Interface and Cockpit
Embedded Computing for Low Power Mobile Applications

Introduction

Mobile applications such as cell phones, laptops, and computers in automobiles all share the following requirements: low power consumption, compact size, and customizable I/O (Input/Output) pins. There are many embedded solutions for mobile applications, yet, due it's ability to run a wide variety of operating systems, the SBC (Single Board Computer) is one of the most commonly used embedded solution. This paper is a review of commercial applications of SBCs, their underlying technologies, and possible methods of implementation in a solar powered vehicle.

The most important requirement of an embedded computing solution in a solar car is low power consumption. Next, compact size is desirable due to limited space in solar cars. Lastly, since the embedded computing solution will be required to store data from a variety of sensors, such as temperature, speed, and energy, customizable I/Os are also preferable for the possibility of installing additional sensors in the future.

One SBC that meets the above requirements is the TS-7250 SBC [1,2]. It only requires a two watt power supply to operate. To put this power consumption into perspective, an average personal computer, such as the HP Pavilion Desktop Series, has a 250 watt power supply [3]. The TS-7250 SBC also meets the compact size specification, with the board dimensions being 3.8 x 4.5 inches. Lastly, the TS-7250 SBC has 20 digital I/O ports. The data received from these ports can be stored on the board's 32 MB flash memory or an optional 128 MB flash memory upgrade. If more storage is required, there are two USB ports that support external flash memory.

The starting cost of a TS-7250 SBC with 32 MB of memory is $149. The SBC with 128 MB of memory is $189. The use of SBCs can be seen in solar powered race vehicles such as the ones participating the World Solar Challenge in Australia [4]. Teams such as the Solar Jackets from Georgia Tech and Principia Solar Car from Principia College are using PC 104 SBCs to collect telemetry data from their solar powered cars. Other common applications include using SBCs to run games such as slot machines and creating low power computing clusters [5].

One of the underlying technologies that make SBCs a great solution for embedded computing is the ARM (Advanced RISC Machine) processor [1,2,6]. The ARM processor provides an instruction set that is useful for data manipulation and does not require extensive training to learn [7]. These processors also support many different operating systems such as Windows CE, Unix, and several Linux distributions. The ability to choose an operating system gives flexibility to the methods used for interfacing with the I/O ports. The performance of ARM processors range depending on its cost. For example, the TS-7250, which is a low end SBC, has a 200 MHz clock. This provides enough computing power for on-board systems in automobiles to analyze real time data [8]. A high end SBC, such as the Texas Instruments Sitara, contains a 1.5 GHz ARM processor [9].

One of the reasons SBCs are able to achieve high performance along with low power consumption is due to the fact that these boards are fanless. Convection cooling means that no power is wasted on cooling the system. This design also contributes to the small size. Without the need of bulky fans or heatsinks, the SBC's size depends only on the I/O ports and the processor. Although the SBC itself is small, the space required for installation can vary with types of I/O devices used.
Implementation of Technology

As an on-board computing solution for a solar car, the SBC begins by receiving input data from the digital I/O ports. These I/O ports are connected to various types of digital and analog senors. In the case of an analog sensor, the data is first sent through an on-board A/D (Analog to Digital) converter, and then sent to the SBC's flash memory. Digital sensor data can be directly stored in memory. Software written to interpret the data is continuously running on the ARM processor. For example, a program can be created that monitors the data received by the temperature sensor and displays it on a LCD screen connected to another I/O port. Another program can continuously poll the data for certain events such as high temperatures or system failures. These programs can be written in a variety of programming languages, depending on the operating system and sensors being used.