122-28176 Parallax Inc, 122-28176 Datasheet - Page 93

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Chapter 4: Sequential Processes and Optical
Switches
Sequential processes are those that follow a defined sequence of actions based on events.
Events involved in a sequential process may be time based, where different actions occur
with defined intervals of time. One example is a clothes dryer, where the sequence of
drying occurs at set intervals. The dryer applies heat and rotates the drum for 50 minutes.
After that time the heat is turned off while the drum continues to turn, providing a cool-
down cycle for 5 minutes. After 5 minutes of cooling, the drum stops rotating and the
buzzer sounds.
The events may also be input based, such as a button being pressed or a sensor detecting
a condition which sets a sequence of actions in motion or allows the sequence to
continue. Consider a clothes washer. What types of events are involved?
Which of the above events are most likely input based, and which are time based? Filling
the machine is an input event since a sensor is used to detect the water level. The
remaining are most likely time based.
There exists a wide variety of input devices and sensors used to detect the absence or
presence of an object or material. Many of these are non-contact in that there is no
physical contact between the sensor and the condition being sensed. Examples include
capacitance, inductance and magnetic. A very popular class of non-contact sensors are
optical; they use light for detection or transmission of data.
wavelength of light is in the infrared (IR) range not visible to the human eye.
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The start button is pressed.
Water valves open and the tub fills to a defined level based on load size with a
detector sensing water level.
The agitator begins to cycle.
Agitation stops and the spin and drain cycle begins.
And so on....
In many cases, the