set Pull

Tell a digital pin use either a high voltage or low voltage to mean that the input signal is off.

pins.A0.setPull(PinPullMode.PullDown)

When you want to use a digital pin to receive an input signal, the pin normally has a pull direction. This means that while the pin has no input signal, it reads true if the pull direction is up. But, if the pull direction is down, the pin reads false.

To set the pull direction, you decide which voltage you want (high voltage or low voltage) to mean that an input signal to the pin is turned off. The microprocessor on your board will connect the pin to high voltage if you set it to pull to up and it will connect it to low voltage if you set it to pull down.

Now, when you want to cause a signal on the pin, you attach your switch or a sensor so that it connects the pin to the opposite voltage of the pull direction you gave it. So, for example, if you set pin D7 to pull up, you attach one lead of a switch to the pin and the other lead of the switch to low voltage (GND). When you press the switch, pin D7 is now pulled low by connecting it to the low voltage. We call the pin signalled when this happens.

Of course, if the pin’s pull direction is set to down, the pin is signalled when it is connected to high voltage (pulled high).

You can have code that waits for a pin to change from high to low, or low to high. This is called a pulse event.

Parameters

• pull: the pull direction to give the pin

  • up: the pin is pulled up (set to high voltage) when it’s not signalled and will read true.
  • down: the pin is pulled down (set to low voltage) when it’s not signalled and will read false.
  • none: the pin is not connected to either high or low voltage. An external resistor or other electronics will make the pull direction.

Example

Set the pull direction for digital pin D4 to up. Flash the LED connected to pin D13 for one-fourth of a second when pin D4 is pulsed low.

pins.D4.setPull(PinPullMode.PullUp)

pins.D4.onPulsed(PulseValue.Low, () => {
    pins.D13.digitalWrite(true)
    pause(250)
    pins.D13.digitalWrite(false)
})

See also

digital read, on pulsed, pulse in