When a digital signal is not connected to either positive (+) or negative (-), the signal is said to be “floating”. Floating simply means that the signal is not connected to anything. This will result in giving false indications when connected to an input which is expecting either a positive or negative signal. To solve this problem, one can use a Pull-Up Resistor or a Pull-Down Resistor, depending on what is needed. The figure below shows the correct way to wire a Pull-Up or Pull-Down Resistor for an active Device or Sensor with an output signal.
In general, the pull-up or pull-down resistor should have a larger resistance than the logic circuit's impedance. A good rule of thumb is that you want a resistor value on the order of 10kΩ or higher. Personally, I have had to use Pull-up and Pull-Down resistors for my Arduino projects as well as for reading fan speed on fans which have a tachometer output.
To learn more about Pull-up or Pull-Down Resistors please visit these sites:
- https://www.douglaskrantz.com/ElecPullUpResistor.html
- https://learn.sparkfun.com/tutorials/pull-up-resistors/all
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