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MODULAR INSTRUMENTATION DESIGN

Part 1ýDefining the Project
by Bob Perrin

Start • The Problem ý The Solution ý Mechanical Interface ý Man Machine Interface ý Electrical Interface ý API ý In Closing ý Sources and PDF

THE SOLUTION

To solve this problem, we must examine it from at least two opposite points of viewýone from the application developer, and one from the embedded system designer.

Figure 1 models an instrumentation project as an onion. While not very original (and a little agrarian for my tastes), the model is illustrative.

Figure 1ýProjects, like onions, have many layers.

The system developer sees the outside of the onion. The API, the electrical interface, and the mechanical interface are the only things the system developer really wants to be concerned with. The controller must be designed to present comprehensive, yet simple interfaces to the developer.

The embedded-system engineer sees the onion from the inside out. The engineer must be concerned with firmware, BIOS, drivers, busses, memory, and CPU interfacing.

Managers love to prattle on about the relative merits of top-down verses bottom-up design. But in my experience, Iýve found the best way to approach an engineering task is through common sense. Look at the project from all sides.

If you strictly take a top-down point of view (the developerýs POV in this case), you may miss certain optimizations that technology offers. Top-down often yields a more expensive than necessary solution.

Working solely from the bottom-up yields a system that has awkward interfaces for the developer. Bottom-up designers will discover interesting or cost-effective technology and build a system around it, creating a device that requires the end user to jump through hoops to make the system work.

So, a kind of three-dimensional common-sense approach to product definition and development is required. First, weýll look at the onion from the developer's point of view while keeping in mind technologies that may be used to economically implement the end system.

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