Tear Down: Scientific calculator boils design down to two ICs
Definitely over-engineered
An interesting aspect of the 35s is that it takes "over-engineering" to a new level. For example, it's held together by 25 screws. Kim explains, "The keyboard is the most important part of a calculator. It must work year after year. Those 25 screws hold it down rock solid. The keyboard will never get loose and this thing will last forever. It costs us more, but it demonstrates the attention to detail we've put in."
If the 25 screws weren't enough, the engineers decided to add a slew of plastic hold-downs on top of the circuit board. As a result, I had to literally break off each of those hold downs to get the board out.
HP claims that it performs a one-million key press-test on the keyboard. This means that the keyboard will survive at least a million key presses. Putting that in perspective, it's unlikely that a user will ever reach that number of key presses.
HP put the 35s through 11 different abuse tests and 20 common tests. These generally have to do with temperature thermal shocks, drops, etc. Many of the tests highlight common occurrences that a handheld calculator would be subjected to in everyday use, but others are abuses that a users will likely never subject the calculator to. They do environmental tests, using the calculator at 55°C, for four hours. Then it's stored at 65°C, with 95% relative humidity, for 120 hours. There are similar tests for low temperatures. The team isn't satisfied unless they get 100% of the tested units to pass.
Unlike one of the predecessor models (the 41), there's no way for the user to tap in to the 35s' firmware. The programming only occurs at the user level, although HP is tinkering with giving users limited access to the firmware.
Kim offers, "The 35s is pretty much hacker-proof, but the old 41 had a lot of hacking going on because it was more of an open platform. There was something called synthetic programming, and there was a crowd that evolved around it. I was actually a member of that crowd, the diehard HP users."
Despite all the testing and over-engineering, the key to building a popular and powerful scientific calculator comes down to basics--making it easy to use, programmable, with all the functions a user would want, all accessible via the keyboard using a simple menu structure.
Richard Nass is editor in chief of Embedded Systems Design magazine. He can be reached at rnass@cmp.com.
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