ME 445 – H12
Name _________________________
1) We wish to measure a signal with maximum frequency content of 4 Hz that also has noise
from AC electrical power. Design a minimum order analog filter to maintain good signal
integrity that will attenuate at least 99% of the dominant noise.
a) Based on the specifications given above, what type of filter, what order filter and what cutoff
frequency would you use? Be specific and justify your answers.
type ____________________
order ____________________
fC ____________________
b) Draw your filter circuit. Include appropriate component values and computations to justify
them.
2) We wish to sense when the SPST switch shown below is closed in a factory environment.
Complete the circuit diagram to provide optical isolation for the computer digital input. Be
certain to use resistors where appropriate and show values of resistance. Support these values
with calculations.
Opto-Isolator
LED: max allowable current = 10 mA
Photo-transistor: max allowable collector current = 100 mA
max allowable VCE = 40 VDC
Switch
max allowable current = 1.25 A @ 50 VDC
Computer
+5 VDC
Factory
+15 VDC
Computer
TTL input
SPST
switch
Optoisolator
Factory
ground
to TTL
Computer
ground
to TTL