# ECE 1250 Labs

Electrical Engineering is about ‘what can you do to a voltage or current’? Throughout the semester, we will be learning about many different ways to control the voltage and current in a circuit.  For example, voltage and current dividers split (or add) voltages and currents, amplifiers increase (or decrease) them, inverters reverse their polarity (multiply by -1) and more.  Each lab will provide you with a set of skills (such as how to measure V,I,R, design and specify the correct parts, build and test circuits, and more).  The overall labs this semester will focus on resistive and capacitive sensors.  Resistance and capacitance can be used to measure temperature, pressure, proximity, moisture, and more. They basically take data from the outside world.  The circuits we connect them to will give information back to us (such as turning on a light if something gets too hot).  At the end of the semester, you will be ready to build a resistive or capacitive sensor system of your own design, and the last few weeks of lab will be a Rube Goldberg (Links to an external site.) design to build a sensor to do SOMETHING, anything!  You choose, you design, you build.  This can be relatively simple, using the concepts from the labs in class (and yes, that is sufficient to do well in the lab).  Or, this can be as advanced as you would like to make it.  So, as you move throughout the labs this semester, start to think about ways you might use the circuits and concepts from each lab and combine them into a sensing system for SOMETHING….

Lab 0a — Multisim V-R in series Simulate a very simple V-R circuit with Multisim.  The most important thing about this assignment is getting Multisim running on your computer.  You will learn the basics of putting down circuit elements, simulating the circuit response, and ‘measuring’ voltage and current in Multisim.  I hope you are also familiar with the online resources for Multisim including tutorials, etc.  You will use these resources throughout the semester.

Lab 0b — Multisim 3way switch Simulate a 3-way switch with multisim.  You will explore a few more circuit elements (switches and bulbs), and see how Multisim simulates the action of the circuit (not just V and I measurements).  It is also a cool puzzle to think through how a 3-way switch works in your house.  By the end of this assignment, I hope you are pretty comfortable with Multisim.

Lab 1 – Measuring Resistance and Resistive Networks

We will be measuring resistive networks and setting up/measuring two potentiometers in series. This most important thing about this lab is getting the MyDAQ running on your computer and acquire the basic components for building a circuit (protoboard, wires, resistors, pots).  You will then use the MyDAQ to explore and verify simple resistive networks, and the potentiometers.  Another important skill and understanding from this lab is being able to use the protoboard to build your circuit (in this case, the pots in series).

Lab 2 – Measuring Voltage, Current & Resistance

In this lab you will measure voltage and infer current from voltage measurements.  You will Calculate, Simulate, Build, Test (and compare these) for a serial/parallel resistive network, and voltage and current dividers.  You will also design and build a resistance indicator (a light that will go on/off depending on the resistance).   Beginning debug skills.

Lab 3 – R2R Ladder for Digital to Analog Conversion (DAC)

In this lab you will build an R-2R ladder Digital-to-Analog converter for converting binary numbers to analog voltages.

Lab 4 – Thevenin Equivalent Circuits

In this lab you will build simple linear circuits consisting of v-sources and resistors, measure the output voltage of the linear circuit with various load resistances,find an equivalent Thevenin circuit consisting of a single voltage source and resistance that has the same output characteristics as the linear circuit,design a voltage reference whose Thevenin equivalent matches given specifications.

Lab 5 – Resistive Sensors

In this lab you will:

• Test several types of resistive sensors:
• Thermistor (R changes with temperature)
• Photoresistor (R changes with light)
• Graphite resistor (R changes with width, length – use this as a moisture sensor)
• Build two types of circuits that respond to changes in resistance:
• Op amp switch (for your thermistor and one other sensor of your choice)
• Op amp inverting amplifier (for your thermistor)

Lab 6 – Digital Gates

In this Lab you will simulate and measure basic logic gates (NAND, XOR, NOT, OR) and design a control circuit for a 7-segment display display.   This lab introduces digital logic gates that are the basis for computer circuits.  You will learn about basic types of gates, and you will design a simple circuit for summing one-digit binary numbers. Logic gates will also be useful in your final project if you need to turn on an LED or motor when a certain combination of sensor inputs occurs, such as “the output of sensor 1 is low AND the output of sensor 2 is high.”

Lab 7 – Level Shifters

In Lab 7 you will:

• Build several level-shifter circuits that shift voltages coming out of a comparator to voltages appropriate for the inputs to logic gates.
• Calculate the output voltages of various level-shifter circuits.
• Measure the output voltages of various level-shifter circuits.
• Design a level shifter circuit.
• Plot the output voltage of a level shifter circuit.

In your final project, you will have an analog voltage from a resistive or capacitive sensor, and may want to convert it to a digital voltage so you can work with it in the digital domain.  This lab deals with the problem of changing voltages from analog (the output of your op amp comparator) to digital levels appropriate to drive digital logic gates.  Circuits that map voltages from one range to another are called level-shifters.  It is common for different parts of a circuit to have different power supply levels, and some voltage translations are so common that special level-shifter IC’s are designed for them.  In this lab, we will see how to design several kinds of level-shifters.

Lab 8 – Capacitors & Capacitive Sensors

In our previous labs, you have used resistors as sensors.  In this lab, we will use capacitors instead.  You have measured DC voltage, and current, but in this lab, you will measure voltages and currents that change with time using a function generator and an oscilloscope.

Lab 9 – Final Project – Week 1 (PDR)

Lab 9 – Final Project – Week 2 (CDR)

Lab 9 – Final Project – Week 3 (FDR)

Lab 9 Extra Credit — Post a video of your final project

Invent, design, simulate, and build a sensor system of your own devising.  Choose and/or build an R or C sensor. Build the circuit to have this sensor do something.  It can turn on a light, motor, or buzzer, for instance.