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LOOKING AT THE SPECS

by Gerard Fonte

Start ý Are You Flexible? ý Whoýs the Boss? ý So, What are Your Options? ý What are the Hazards? ý To be or Not to be Specified? ý Unhappy Customers ý Sources and PDF

SO, WHAT ARE YOUR OPTIONS?

What do you do if you are presented with a project that requires impossible specifications? For example, letýs say that marketing has promised to measure ý0.1ýF with your standard embedded microcontroller. The problem is that the microcontroller has an 8-bit A/D and is specified as 0ý to 200ý, ý2ý. Obviously going from 0 to 200 in 0.1 steps requires at least 11 bits (2048 steps).

There are a few things that you should remember, everything in marketing is negotiable, marketing has a potential sale, and marketing is not engineering. So, sit down, take a breath, and think things through. Examine all the options and possibilities. Remember that someone has told marketing this is what they want. But, who told them, an engineer or a manager? What application is this for? How much extra cost will be acceptable? What is the likely volume of sales?

After examining the problem in detail, you should have a meeting with marketing (or whoever gave you the specifications). First, show them the cost of adding an out-board A/D converter (software and hardware) and whatever else is needed to perform the task. Then explain why the existing system canýt work. It is always good practice to give a solution first, even if itýs unlikely to succeed. It shows that you are working on their problem, not dismissing it. Get as many details from marketing as possible. If itýs possible, a technical discussion with the customer would be useful. Often, these impossible specifications are a result of miscommunication or wishful thinking.

In this case, the application was for monitoring the body temperature of zoo animals. Clearly the range of temperature is small, and an 8-bit A/D will resolve 0.1ý from 95ý to 105ý (100 steps).

But wait! There is an important difference between resolution and accuracy. Determining the actual temperature (i.e., 98.6ý) to ý 0.1 requires a precision sensor. The temperature sensors used in such a situation only provide absolute accuracy to ý2ý. So, a real temperature of 100ý could be measured as anywhere from 98ý to 102ý. This is not accurate. But, it turns out that the animals are generally healthy. So when the system is turned on, the first reading is the normal temperature. All that needs to be measured is a change from normal (accuracy refers to an absolute measurement; resolution refers to a relative measurement).

In short, by re-examining the problem, a small design change to the system allowed the standard microcontroller to be used. This makes marketing happy, the customer happy, and you get a hearty pat on the back. In general, when faced with impossible specifications, find a solution first. It may not need to be a great solution, but donýt simply say, "It can't be done." Marketing and management view this as poor teamwork.

It may come to a point when it is impossible to achieve the specifications as presented. For example, use the onboard 8-bit A/D and measure 0.1ý over 0ý to 200ý (without range-changing). In such a case, marketing and management are willing to ignore or falsify the specifications in order to make the sale. Although rare, this has happened (e.g., military programs that donýt work). You will have to choose between your job and your character. Be careful not to get roped into being the scapegoat. It will eventually be discovered. Written documentation is vital in this situation.

If you are working for yourself, the situation may arise when the customer presents an almost working product that needs tweaking. This is tricky. Again, provide a solution for your customer and explain in detail why it is necessary. If you take the job, be sure to have everything detailed in writing. Often these customers donýt understand the solution. If they did, their product would work.

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