Allow forcing a read and a few fixes #38
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This allows forcing a read, even if the previous read was less than 2 seconds ago. This is useful in cases where the millis() timer is not reliable, such as when sleeping. In this case, it is up to the caller to ensure that at least 2 seconds elapse between calls with force set to true.
There was some handling of millis() overflow that is not needed. Standard unsigned subtraction and wraparound already works as expected, so this extra check can be removed (it even hurts, since it introduces 2 seconds after a wraparound where no new data will be read, even if it could otherwise happen). Also, this prevents calling millis() a second time, since its value is already known.
By cleverly setting _lastreadtime in begin() to make sure that it looks like the last read was alrady 2000 ms ago, even on startup when millis() still returns 0, there is no longer a need to keep a separate firstreading variable, saving a byte of memory and a bit of code.
There's only 5 bytes of data being transferred (2x2 bytes of data, 1 byte checksum), so no need to keep a useless byte.
Previously, the mode was configured to INPUT and then written HIGH, which works on AVR but isn't very portable. Instead, this uses the INPUT_PULLUP pin mode (available since Arduino 1.0.1) which is portable.
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@tdicola, any chance to merge this soon? I'm using this library in my book (which I'm finalizing this week), so I'd like to refer to a released version if possible. Of this commits, I really need the |
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Awesome thanks for submitting those great fixes! Just gave it a quick test on an Uno and everything works well. Merged it in and will bump the version number so the library manager picks it up. Thanks! |
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I've found that when the Arduino employs sleeping, it can no longer properly read the sensor since millis() doesn't tick while sleeping (and the library now insists that the Arduino has been awake for 2 seconds since the last reading). I fixed this by adding a "force" parameter to the read methods.
While I was there, I did a few more cleanups of some code I encountered along the way, which should slightly simplify and shrink things (without losing any functionality).