Whether you're pulling-up or pulling-down, there's no need to frown! With the PUD board from ModMyPi, adding multiple pull-up or pull-down resistors to your Raspberry Pi project is easy! We have a full HAT version of this board available here.
If you want to detect an "output" with your Raspberry Pi, like a button being pressed or a motion sensor detecting movement, we can configure our Raspberry Pi's GPIO pin as an "input". That input pin can be in three states (known as Tri-State logic); "high", when 3.3V is applied, "low", when the pin is connected to 0V, and "floating" when the state is undefined. Floating voltages are troublesome in electronics as the input can either read high or low depending on various fluctuations in electrical noise. Like a gate flapping open and closed in the wind, someone needs to lock the gate closed, or wedge it open. If you leave it flapping, it's likely to hit someone on their bottom on the way through!
Like our gate, the best way to avoid a floating input is to "tie" your input pin either high or low to create a default state. This is usually achieved through the use of a pull-up or pull-down resistor, either connecting our input pin via a resistor to the Pi's 3.3V to achieve a 3.3V high state, or the GND line to achieve 0V low state.
Our PUD board takes the messy wiring out of adding a pull-up or pull-down resistor to your circuit. Simply wire up the sensor output to the single pin on the PUD board and add a shunt jumper to either pull up (u) or down (d)! Therefore when you apply a signal voltage from your sensor or switch, the Pi is easily able to sense into which logic state the pin has been pulled! No more trouble from floating I/O's!
The PUD boards connects across GPIO pins 11 to 18 (17 to 24 in BCM speak), and adds a jumper configurable pull-up or pull-down resistor to each GPIO pin: 11 (BCM 17), 12 (BCM 18), 13 (BCM 27), 15 (BCM 22), 16 (BCM 23) and 18 (BCM 24). Pin 17 (3.3V) & pin 14 (GND) are used to tie the pins!
The PUD Board Features:
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