Design Con 2015

Pick the right wireless sensor/controller for your connected MCU-based design

Kim Rowe, RoweBots Research Inc.

May 15, 2012

Kim Rowe, RoweBots Research Inc.May 15, 2012

A plethora of competing wireless technologies are sprouting all around us. But even before you take the first steps to implementing one of them into your design you need to ask yourself: How can we introduce this into our products at low cost? What benefits are there for the users of the products we design? The range of benefits are significant:

* Wireline connections for sensors can be eliminated simplifying analysis, production and control systems.

* Universal remote control devices like tablets and phones can be supported at low cost.

* Lower cost installation is achieved through the elimination of wiring for control signals.

* Lower cost maintenance results from elimination of troublesome wireline connections and the need to move wires from time to time.

* Significantly more data can be captured and retained.

* Enabling new types of analysis based on the new or integrated data leads directly to improved management decision making.

* Simple connectivity of a broad range of devices using a variety of alternate wireless technologies can be easily achieved.

MCU and MPU Design Pitfalls
Because there are so many competing technologies you have to factor in several things as you make your assessment. First, as a designer, you must choose wisely to avoid obsolescence. Ultimately, the technologies will be standards driven but experience tells us that different standards will dominate different application areas and that competing standards may evolve in parallel for long periods of time. Defacto standards can also be successful for narrow applications if pushed by the dominate player in that segment.


Click on image to enlarge.

Figure 1: This shows the various competing technologies and their various data rates along with some measure of range. The GPRS 2G, 3G and 4G are shown in terms of their distance and power from the tower, as all options can be back hauled through a wireline network. This provides a direct technology comparison. The difference is that GPRS comes complete with the back haul system while other wireless choices do not necessarily have this.

Tradeoffs between power, range and data rate are critical. Figure 1 above shows the various competing technologies and their various data rates and ranges. Figure 2 below shows the required power for the various technologies. When the application is analyzed, be sure to leave margins in the system that you choose (in data rate, power and range) for future expansion.


Click on image to enlarge.

Figure 2: This figure shows the combination of data rates and ranges by technology along with battery requirements for prolonged use. It is expected that GPRS options require much greater much more power which is reflected in their much greater range.

The cost of using a particular technology may be an issue. While a GPRS connection carries a cost based on traffic or time, a wireline internet connection may not. Be sure to choose a technology that fits your application in terms of the business model for the system.

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