It begins ¶

In order to create an authentic movie-experience at home I own a projector (enjoy with flavacol for extra authenticity). In 2015 I discovered AtmosFearFX which is a company that produces content meant to be projected onto walls or out of windows or onto curtains. For our front-room I project a ghostly apparition onto a sheer curtain so that it roughly looks like it’s walking around inside. This has been a big hit with trick-or-treaters, so much so that I bought a(n extremely crappy) mini projector that I would never be able to use for movies, but – none-the-less – works great for projecting weird zombie hands groping for freedom on the window of our porch.

This was the same year I began incorporating microcontrollers to trigger effects. I built a project with a Particle core attached to a reed switch on my front door. The Particle board sent a web request to my hue light bulb on the porch (scream sound warning):

Now ¶

Fast-forward a few years and my setup has become even more elaborate. Sometime around 2016 I began fooling around with pneumatic pop-ups. After a few DuckDuckGos I stumbled on FrightProps and subsequently began spending too much money there.

My big project this year is a pneumatic pop-up that uses an air-compressor. This is controlled by a motion-sensing Raspberry Pi.

The key component is the solenoid:

This controls the 30PSI (or so) coming from my air compressor to a pneumatic cylinder. The solenoid is controlled via 12V. This is more than my Raspberry Pi is capable of pushing out over GPIO. Fortunately, I have an Adafruit MotorHAT. The MotorHAT has its own 12V power supply and can be controlled by a Raspberry Pi. I also used a PIR sensor to detect motion and trigger my popup.

The pop-up dummy itself is made out of 1/2" PVC tubing, zip ties, a skeleton I bought at Home Depot, and love.

I control the whole contraption with some python code running on the Pi. I’ve wrapped the Adafruit MotorHAT code in (what I think is) a nicer interface for this project:

from Adafruit_MotorHAT import Adafruit_MotorHAT

class Pneumatic(object):
    """
    Abstraction for Adafruit MotorHAT that I'm using as a weird way to drive
    a pneumatic pop-up.
    """

    UP = Adafruit_MotorHAT.FORWARD
    DOWN = Adafruit_MotorHAT.RELEASE

    def __init__(self, motor=4):
        """
        :motor: Integer - 1-4. Motor output to use on the MotorHAT
        """
        mh = Adafruit_MotorHAT(addr=0x60)
        self.pop_up = mh.getMotor(motor)

        # Max motor speed is 255
        self.pop_up.setSpeed(255)

    @property
    def is_up(self):
        return self.status == UP

    def up(self):
        self.status = UP
        self.pop_up.run(self.UP)

    def down(self):
        self.status = DOWN
        self.pop_up.run(self.DOWN)

Which lets me test-drive the setup pretty easily via ipython:

>>> from scary import Pneumatic
>>> motor_output = 4
>>> popup = Pneumatic()
>>> popup.up()
>>> popup.is_up
True
>>> popup.down()