Accelerating parallel product development with 8- and 32-bit compatible devices

by Ralf Lehmann, Field Applications Engineer, Future Electronics (Germany)

READ THIS TO FIND OUT ABOUT: Hastening development of products that offer variants with different performance levels Development tools annd devices that enable 8- and 32-bit development

In June 2007, Freescale Semiconductor introduced its Flexis™ series of microcontrollers, a product line that offers pin- and software-compatibility between 8- and 32-bit devices. Flexis offers design engineers the prospect of developing families of end-products that share a common hardware platform and code, but that have varied needs in terms of performance. Ralf Lehmann, Field Applications Engineer, Future Electronics (Germany) explains.

This article describes an example of one Flexis end-product design: a rainwater harvesting system. The low-end member of the Flexis family is a simple meter with read-out; the high-end product, however, carries out metering and supports a wireless control panel that provides system information and enables choice of using either stored water or mains water.

The Flexis family includes 8-bit devices optimised for performance, price and power consumption; and 32-bit devices, which use Freescale’s popular ColdFire® core, offering about six times more processing speed and support for Flash memory sizes higher than 128kB.

In the rainwater harvesting design, the Flexis family enables the design team to share common hardware components, code and development tools across every end-product. This accelerates time to market, cuts materials purchasing costs and streamlines manufacturing.

 

Development boards for parallel proof-of-concept

At the same time that Freescale launched Flexis, broadline distributor Future Electronics introduced its CrossBow Future-Blox development board. CrossBow supports various 8- and 32-bit Freescale microcontrollers, including the QE devices, hosted on plug-in daughterboards.

CrossBow adopts the Future-Blox stackable board format introduced by Future Electronics in October 2006. This format allows designers to plug together combinations of controller and application boards to quickly build complete proofs-of-concept.

CrossBow supports a wide array of peripherals and communications interfaces, addressing all the mainstream requirements of industrial and consumer 8- and 32-bit MCU users. It comes with a free version of Freescale’s CodeWarrior for Microcontrollers development-tool suite.

In the rainwater harvesting system described below, the combination of CrossBow and Flexis eliminates the need for designers to reinvent the wheel and allows them to focus on end-user functions.

 

 

An overview of rainwater harvesting systems

Rainwater harvesting systems collect and store rain from roofs or ground surfaces for future use. This is appropriate where there is enough rain for collection, but conventional water resources either do not exist or are at risk of being over-used to supply a large population.

In affluent countries, rainwater harvesting is often a means for organisations or individuals to reduce their consumption of natural resources. In less affluent countries, rainwater harvesting can be an essential life-support mechanism.

These differing markets require different rainwater harvesting systems. At the low end, for example in much of the developing world, the requirement simply for a stand-alone water-level meter with LCD. This allows users to regulate water usage according to supply. Such a product needs to be optimised for power consumption, as it will often be battery-powered, and cost. An optional ZigBee™ RF interface can add value whilst lowering the cost of installation, particularly for multi-tank systems.

The high-end version is a mains-powered system controller for use in hybrid rainwater/mains water applications. This includes the same water-level metering function and ZigBee interface as the low-end product, but also enables sophisticated control of water usage, automatically switching supply from stored water to mains water when the tank runs dry. An LCD and keypad give the user additional system information and usage options. The controller also drives peripherals such as the pump and valve switches via RS-232, USB, CAN or simple wireless connections.

 

 

The design uses a pressure sensor to measure the water level. This is linked to a stainless steel weight with a tube fixed to it, placed on the base of the water tank (see Figures 2 and 3). The higher the water level, the higher the pressure detected by the sensor.

Basic control of rainwater harvesting itself is not a heavy-duty processing task, and could be accomplished by an 8-bit microcontroller. The high-end system controller, however, needs to interface with the ZigBee, CAN or USB protocols that building automation systems employ. These protocols run software stacks that require more memory and processing performance than an 8-bit microcontroller can provide. Flexis, and the CrossBow board from Future, together provide the flexibility to design in such functions easily on to a common hardware and software platform.

 

Rainwater harvesting devices

The functions of the stand-alone water-level meter are common to all the rainwater harvesting product variants. The system consists of a pressure sensor, the MC9S08QE128 microcontroller and an LCD module (see Figures 3 and 4 for sensor module).

 

 

Adding an IEEE 802.15.4-based RF interface and a simple point-to-multipoint networking stack makes the device more suitable for large installations.

A full-blown system controller is much more complex: When a water tap opens, the pressure in the supply pipe drops. This change in pressure triggers the system controller to switch the pump on until a pre-set pressure of 4 bar is reached.

If the level in the tank drops below 5%, the system controller switches to a mains water supply or, in a multi-tank system, it switches to a full tank.

This means the system controller must not only measure the water level in one or more rainwater tanks, it must also monitor the pressure in the supply pipe, control the pump and electro-magnetic switches, and enable user interaction via a display screen, signal LEDs and a keypad. The control and man-machine interface elements must support sophisticated communications protocols such as ZigBee, CAN or USB.

 

 

Realising a prototype quickly and easily

What makes this application so quick and easy to design is that all of the necessary functional elements described above are supported by Future Electronics’ CrossBow board. Unlike any custom board, or the restricted-use evaluation boards provided by some IC manufacturers, CrossBow supports complete proof-of-concept development, including application software.

For the simple water level monitor, CrossBow provides a daughterboard carrying the MC9S08LC60 microcontroller. This device has a direct LCD interface, which makes it possible to use a cheap glass LCD. This controller can also drive segments of the LCD in sleep mode, which dramatically reduces power consumption.

Alternatively, the water level meter with RF interface uses an MC9S08QExx device, because it offers good memory scalability. This change of microcontroller is accomplished by simply swapping daughter-boards on CrossBow. In point-to-point configuration, this product can use the MC9S08QE64, but it can easily be upgraded to a ZigBee version, requiring more Flash memory, by swapping over to the MC9S08QE128.

Upgrading to the full-blown system controller simply requires a change of daughterboard, with the Flexis MCF51QE128 device used to handle a networking protocol such as CAN or USB.

The CrossBow board also provides a socket for a MaxStream XBee® Pro ZigBee radio module. This module is available in both IEEE 802.15.4 and ZigBee versions. It is connected via a serial RS232 interface to the controller.

CrossBow’s connector in Future-Blox format can connect to up to eight sensors, so a CrossBow prototype can control up to eight rainwater tanks – adequate for nearly all applications.

The CrossBow board also carries Avago Technologies’ HSMF-A341 RGB LEDs used in the high-end product as indicators for monitoring functions such as system status, battery status and tank/mains supply.

 

 

The use of the resources provided by CrossBow can be seen in Figures 5 and 6. Figure 5 demonstrates a proof-of-concept of the water level monitor. It shows the pressure sensor module (blue PCB), the MC9S08LC60 Mini-Blox daughterboard on the CrossBow board, and the LCD module. The bar graph in the top right corner of the LCD shows the water level, with five bars representing 100%.

 

 

Figure 6 shows the high-end system controller proof-of-concept. Here, the LCD shows the message that the tank level is below 5% and that the system has switched to a mains water supply. In this basic configuration, without any communication module, an 8-bit Flexis MC9S08QE64 MCU is adequate, but its software runs successfully on the 32-bit Flexis MCF51QE128 MCU without any modification, other than changing the CodeWarrior compiler target to MCF51QE128.

 

Conclusion

Both systems were developed and tested extremely quickly and the family of products produced meets the strictest requirements of flexibility and manufacturing cost. The CrossBow board makes this kind of development possible by providing a modular, 8- and 32-bit compatible, feature-rich platform.