Electronic Design

Interfacing The Sensor

If you haven’t worked with wireless sensors, you may be surprised to learn that the wireless part may be the easiest part of your design. With all the excellent wireless chips, boards, and modules available, the wireless component is often just a drop-in element. The sensor is probably your own, and it will undoubtedly require a custom interface. This analog part of your design will often require more of your time than other parts except perhaps the programming of the embedded controller.

Sensor interfacing is a mix of amplification, filtering, and other signal conditioning as well as analog-to-digital conversion. The analog-to-digital converter (ADC) may be in your microcontroller, but you will still need to make the sensor compatible with the ADC input. The sensor company will probably have some suggestions for connections and conditioning, so start there. After that, you’re on your own.

One excellent source of help with sensor interfacing is National Semiconductor’s online Webench Designer Tools. In addition to tools for power designs, National offers a new sensor interface design tool. It covers thermocouples, photodiodes, and pressure sensors from multiple manufacturers (see “Versatile Design Tool Enhances Its Visualization And Extends Its Range”).

After you indicate your choice of sensor, the tool leads you to a recommended design that includes a schematic, full bill of materials (BOM), test data, specs, and other useful info. The designs are the result of many engineers collaborating on an optimum consensus design. The ADC is included. An example shows the design offered by the tool for a Honeywell pressure sensor (see the figure).

You can then buy the parts online from National or a kit with printed-circuit board (PCB) and the main parts to quickly get you to the prototype stage. A data capture board with flash and USB port helps you store the data and provide input to the microcontroller and wireless components. All of this can save a massive amount of time. Check it out as a possible design solution.

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