122-28176 Parallax Inc, 122-28176 Datasheet - Page 223

• 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

resistor. Through a little testing, you can determine just what drive level is needed to
yield the correct temperature.
Recall how PWM was used in previous activities to control the speed of the fan. In this
activity PWM is used to control the temperature of the incubator. The 100 Ω resistor-
heater dissipates 0.81 W of power as heat. If a PWM of 50% is used, how much power
would be dissipated? The resistor would be at 0.405 W of course, or 50% of 0.81 W.
At the correct setting of PWM, the heat into the system from the resistor will equal the
heat lost from the system at 101.5 °F, to maintain a constant temperature. As long as
conditions do not change, the temperature will remain constant.
Parts Required
Same Circuit as Activity #3 (page 203)
Example Program: IncubatorOpenLoop.bs2
' -----[ Title ]-----------------------------------------------------------
' Process Control - IncubatorOpenLoop.bs2
' Drive incubator with a user defined PWM drive
'
' {$STAMP BS2}
' {$PBASIC 2.5}
'
' -----[ Declarations ]----------------------------------------------------
ADC_ByteValue
V_Offset
V_Span
TempF
PWM_Drive
√
Enter, save and run the BASIC Stamp program IncubatorOpenLoop.bs2.
WARNING: Do not use an unregulated wall-mount power supply greater than 9 V for
the remainder of the activities in this text.
supply is recommended. Fresh 9 V batteries may be used, but they will drain very
quickly. The heater resistor will get hot. Care should be taken when touching the
resistor and in construction of the incubator. Do not allow the test tube to touch the
resistor directly; even so, it may warp. Do not set temperature limits above 120 °F.
NEVER LEAVE POWERED CIRCUITS UNATTENDED!
VAR
VAR
VAR
VAR
VAR
Byte
Byte
Byte
Word
Byte
' Analog to Digital Converter data
' Offset voltage read from StampPlot
' Span voltage read from StampPlot
' Calculated temp in 100ths of degree F
' Amount of PWM for heater
A 7.5 V unregulated or 9 V regulated