122-28176 Parallax Inc, 122-28176 Datasheet - Page 187

• 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 5: High Current Drive and PWM Control · Page 177
CONCLUSION
Controlling higher voltage or current output devices is often a necessity when interfacing
real-world process control. The transistor (BJT or FET) is a popular and inexpensive
means of controlling DC devices.
Using PWM, the power to a motor or device may be varied. The percentage of time
HIGH as compared to the total time or period is called duty cycle. Duty cycle values can
range from 0% to 100%. The PBASIC command
provides a means to control the
PWM
duty cycle, but uses values of 0 to 255 to define 0% to 100% duty cycle. A transistor
controlled by the PWM maybe used to control a higher current or voltage DC device.
PWM may be directly applied in many instances, but it is in effect only while the
instruction is being executed. Through the use of RC filters, the duty cycle may be
converted to a voltage from 0 V to 5 V. With the use of operational amplifiers the
voltage can be buffered or amplified. This provides a very high-impedance input from
the RC filter and a very low impedance output to drive the device or a transistor.
Beyond what is explored through experimentation, there exist a wide range of devices
and means of driving devices such as Darlington pairs, coil relays and solid-state relays.
SOLUTIONS TO CHAPTER 5 CHALLENGES
Challenge 5-1 Solution
The higher the HIGH time as compared to LOW time, the faster the fan will run. With
HIGH times 3 ms and under the fan may not rotate due to low voltage.
The LED should be noticeably dimmer with long LOW times as compared to HIGH
times.
Challenge 5-2 Solution
Part A:
The fan's speed drops off faster below 70% duty because of the increased time allowing
the fan to slow more.