Mech I/Basic E – Homework 4
Section 2
Fall 2026
September 23, 2026
Reading: Read over Chaper 5.
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Op Amps Design Problems
Problem 1
(3 pts) Draw an op amp being used as a buffer and explain what it does. Do a little research
into an application and explain why it would be useful.
Problem 2
A longer design problem... As discussed in class, you want to measure the strain in a beam.
Because you are a student with limited funds, you buy some cheap resistive strain gages off the
internet. While testing them, you find that they have a resistance of about 350 Ω, and that
you can change the resistance by only a small amount, about +2 Ω bending one way, and -2Ω
bending the other. You want to use your Arduino to measure the signal, which means your
circuit should output some voltage between 0 to 5V, as an input to the Arduino.
a) You decide to start by using a single gage to measure the strain signal. You remember
hearing that using a difference amplifier and a wheatstone bridge could be useful. Draw your
wheatstone bridge and indicate where you would connect it to your amplifier.
• What values would make sense for the resistors?
• What would the current be going through the circuit?
• Given what you know, what is the difference in voltage that you would expect to see
between your two inputs? What might be a good approximate gain for your difference
amplifier?
b) You ask Claude to pick a cheap and easy to use op amp for you given that you want to
use it as a differential amplifier and need it to output between 0 and 5V. Claude suggested the
MCP6001. The product page can be seen here, and the datasheet is available here. Looking at
the datasheet (and especially the first couple pages):
• What’s the supply voltage for this op-amp? Do you agree with Claude that it makes sense
for our application?
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Homework 4
Mech I/Basic E
Section 2
• What about current? What are typical values for the input and outputs? What about
absolute maximums?
• Given the information you just learned about current, and your desired gain, choose some
resistors for the difference amplifier.
• Components like this op-amp generally have some variety of packages or forms. If you
were making a PCB, you might want a SMD or Surface Mount Device. When using a
breadboard, we’re generally looking for a DIP or Dual In-Line Package. The op-amp
we’re looking at has a PDIP version; that’s the one we want. Take a look at the pin
configurations shown on the first page for MCP6002 (which come as a PDIP). In your
circuit diagram label the pin numbers for the op-amp. Do you have multiple options?
c) You change your mind and decide to have one sensor above the beam and one below, right
on top of each other. How does this help? How does your wheatstone bridge change?
d) You change your mind one more time and want to use four gages. Why might you do this?
What would your wheatstone bridge look like? Would you make any changes to your difference
amplifier configuration?
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