Pololu 0J5840, Руководство пользователя

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The 3pi demonstrating the effects of various motor
settings.
5.d. Digital inputs and sensors
The microcontroller at the heart of the 3pi, an Atmel AVR mega168 or mega328, has a number of pins
which can be configured as digital inputs: they are read by your program as a 1 or a 0 depending on
whether the voltage is high (above about 3 V) or low (below about 1.5 V). Here is the circuit for one of
the pushbutton inputs:
Normally, the pull-up resistor R (20-50 k) brings the voltage on the input pin to 5 V, so it reads as a 1,
but pressing the button connects the input to ground (0 V) through a 1 k resistor, which is much lower
than the value of R. This brings the input voltage very close to 0 V, so the pin reads as a 0. Without the
pull-up resistor, the input would be “floating” when the button is not pressed, and the value read could
be affected by residual voltage on the line, interference from nearby electrical signals, or even distant
lightning. Don’t leave an input floating unless you have a good reason. Since the pull-up resistors are
important, they are included within the AVR – the resistor R in the picture represents this internal pull-
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