8.2 Building the Solution
We have several objectives to complete for our
project to work as intended. First, we will test the stepper motor
by writing a sketch using Adafruit’s AFMotor library. This assumes that you have
already constructed the motor shield. Follow the instructions on
Adafruit’s website for more details on assembling and using the
motor shield.[82]
After we have a working stepper motor’s drive shaft that rotates back and forth based on the instructions we have the Arduino execute, we will hook up the photo resistor. We will borrow from the same light sensor routine we wrote for the Chapter 5, Tweeting Bird Feeder. When this photosensor detects light that exceeds the threshold we establish, the stepper motor drive shaft will spin clockwise for a predetermined number of revolutions. When light diminishes below the low threshold value that we set, the shaft will spin the same number of revolutions in the opposite direction. When the shaft spins, the attached pulley will open or close the curtain accordingly.
In addition to light detection, we also need to account for room temperature in case it exceeds a certain value. If the room starts to get too warm, we can spin the drive shaft counterclockwise to close the curtain even when there is daylight. If the temperature cools off to a comfortable level and it’s still daylight, the shaft will spin clockwise to reopen the curtains.
Once our detectors are working and tested, we will attach the pulley wheel to the stepper motor’s drive shaft. Then we will wrap the curtain drawstring around it and determine where we can mount the stepper motor/pulley assembly on the wall. The location of the assembly needs to keep the curtain drawstring taut enough so that it will not slip when the pulley is revolving. Next we will calibrate the number of revolutions required by the stepper motor to open and close the curtain. After those settings are determined, we can increase the speed (revolutions per minute) of the stepper motor to establish how quickly or slowly the curtain should open or close.
With these steps in mind, let’s first take a look at how we can write a sketch that will control the stepper motor.