122-28176 Parallax Inc, 122-28176 Datasheet - Page 176

• 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

Challenge 5-5: Changing the Gain
ACTIVITY #6: DRIVING THE FAN WITH THE OP-AMP
In previous activities, the PWM duty cycle from the BASIC Stamp was filtered, buffered,
and amplified. The circuit can now produce voltages from 0 to 10 V in 0.0392 V
increments. Can we now drive the fan with it? No, because the output current of the op-
amp is insufficient.
Let's review two key principles:
Consider how Figure 5-20 brings these principles together. With the input to the non-
inverting terminal at 2 V, what voltage will be at to R
provide sufficient base current to reach a point where 4 V is sensed at R
inverting input). The common-collector configuration is used to be able to measure the
voltage across the load to ground.
√
√
√
•
•
Replace R
Calculate:
Test your results for a, c and d above. In testing the results, leave the
for plotting with a value of 0.0392 since the ADC is still spanned for 10 V.
The op-amp will drive its output in an attempt to balance the inputs.
The BJT transistor is a linear device and can conduct up to 200 mA dependent
on base current.
a. The gain.
b. The maximum output voltage predicted for a PWM of 255.
c. The output voltage for a PWM value of 25.
d. The output step resolution.
e. The %Resolution.
f
with a 4.7 kΩ Resistor.
L
? The op-amp will drive to
L
(2 V at the non-
DEBUG
line