122-28176 Parallax Inc, 122-28176 Datasheet - Page 162

• 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

ACTIVITY #3: PWM FILTERING
The inertia of the fan performed mechanical filtering, or damping, to run at various
constant speeds with a quick cycling of high and low voltages. Your eye performed
filtering of the LED blinking on and off rapidly to see a bright or dim LED. Electrical
filtering of a changing voltage can be achieved by the use of a resistor-capacitor (RC)
network.
A capacitor is used to hold a charge of electrons. An RC network, properly sized, can be
used to filter the cycling PWM to a constant voltage.
Additional Parts Required
(1) 10 kΩ Resistors
(1) 100 kΩ Resistor
(1) 1 MΩ Resistor
(1) 0.68 µF Capacitor
√
√
Remove the fan circuit connected to P2 (including its MOSFET transistor, LED,
both 220 Ω resistors, and the fan itself).
Replace it with the RC circuit as shown in Figure 5-11. DO NOT connect R
initially.
L