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adafruit / Adafruit_BMP280_Library

Arduino Library for BMP280 sensors
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Fail gracefully if begin() not called #66

Closed sellensr closed 2 years ago

sellensr commented 2 years ago

Tests _sensorID to make sure begin() was run before other I2C calls are attempted. Returns 0.0 instead of T, P if not initialized. Prevents non-return crashes.

Requires previous pull request #65 that properly sets _sensorID, so it may fail if somebody was home brewing their own begin code. Partially addresses issue #64

I didn't know this was even a potential problem until multiple students tried to readPressure() before begin() this term...

caternuson commented 2 years ago

Is this not solvable by having them correct their code?

How are they missing this even after referencing the library example?

The general issue with this approach is the library functions are setup to return the values of interest. For example, 0.0 is a valid temperature. How would you know that return is an eror vs. an actual temperature?

sellensr commented 2 years ago

Why does tech support always start with "Is it plugged in..."?

Returning 0.0 is better than simply never returning from the function, which is current behaviour if begin() is not called. My experience shows that even the densest students are worried when the result is zero and never changes at all. P=0.0 Pa is physically near impossible. I don't think T=-273.13 C would give as much of a warning as a persistent 0.0.

caternuson commented 2 years ago

Why does tech support always start with "Is it plugged in..."?

Where is that happening? Is this a hardware issue or a software issue?

ladyada commented 2 years ago

the functions could return NaN instead, to indicate invalidity

sellensr commented 2 years ago

the functions could return NaN instead, to indicate invalidity

Good idea

sellensr commented 2 years ago

Is this a hardware issue or a software issue?

It's a software issue -- functions that can be called in the wrong order sometimes will be called in the wrong order, and shouldn't crash when it happens. The inspiration in some cases has apparently been the sensortest example that initializes globals with bmp.getTemperatureSensor() and bmp.getPressureSensor() before calling bmp.begin() in the setup(). Novice students don't get why they can't also say:

double pAmb = bmp.readPressure();

to initialize a global at the start of the program.

caternuson commented 2 years ago

OK, NAN returns do help with avoiding returning potentially valid values. Let's merge this and see if it helps. Or if the new issue just becomes "what's a NAN?".

sellensr commented 2 years ago

Instant gratification! Yesterday I asked some struggling students to try again with the new library and examples and they were able to solve their problems on their own.