Week 2 day 2

Temperature Measurement System  Lab

Pre-lab:
we have to design a circuit containing an NTC thermistor as one of the resistances which satisfy the following specifications:
1) 5V input voltage to the system
2)Output varies by 0.5 V over temperature range of 25celcius to 37 celsius
3) Output voltage must increase as temperature increases

By Looking up the graph of this thermistor, our theoretical thermistor to have resistance of 11000 ohm at 25 degree celcius and 7000 ohm at 37 degree celcius.

 We sketch the circuit and calculated the theoretical resistance needed to be 4633 ohm

In this experiment we pick our resistor value to be 4700 ohm, but further measurement by DMM shows that the resistance of our 4700 Ohm resistor is approximately 4.67 ± 0.01 kΩ
we also measured the resistance of Thermistor  to be 11.8± 0.01 kΩ at room temperature
and 6.65 ± 0.01 kΩ at Tony's body temperature.

Overall Scheme of our breadboard circuit

Close up of our bread board circuit :

 Quick demonstration of our circuit, note that the potential difference across our resistor increases where body heat is applied to the thermostat:

Using voltage sensor on waveform we can see that the potential difference across the resistor starts at 1.5 V and increases to 2 V before it levels up

Measurement using DMM shows that the potential difference of resistor s equal to 1.43± 0.01 V at room temperature and 1.98± 0.01 V at 37 degree celcius:

Nodal Analysis and SUPERNODES Lecture :

review/ quiz : solve the potential difference across Resistor 1 in terms of I1 I2 R1 R2 R3:

Summary:


In measuring and designing our temperature dependent system we used voltage divider formula to solve for our fixed resistor. Nodal analysis is a faster system in solving circuit compared to kirchoff rule. We use nodal analysis method in circuit that have a lot of current supply and a lot of parallel connected element in circuit. When voltage source is present during nodal analysis we have to apply super mesh method.

Week 2 day 1

Lecture

Suicide sausage experiment

what will happen if we connect sausage into potential difference of 120 V?

 Sausage is slowly cooked over time.
Now we connected LED across sausage parallel to the current and perpendicular to the current

LEDs that parallel to the current light up, while  LEDs that perpendicular to the current source doesn't light up. For LED that light up, the farther the distance between the leg, the brighter the LED lights up. After a certain amount of time, the LED turned off.  WE  then sketch the possible current versus time:

Dependent source circuit problem:

Resistor connected in series:

Voltage splitter problem #1,
what is the Potential difference between Resistor 2?

Voltage splitter problem  #2
Find the needed resistor to split potential difference of 12 V to 3.3 V

LED Problem, Find the value of resistor needed to light up the LED

Find the Equivalent Resistance needed for this circuit:

Dusk to Dawn Light Lab

Pre-lab problem:
Find potential difference between photocell given that resistance of photocell is 5K ohm when it's bright and 20K ohm when it's dark :

Measuring the Resistance of resistor:

 Measuring the resistance of photocell when it's bright:

 Measuring the resistance of photocell when it's dark :

Measured Resistance for Photocell and Resistor.

First trial :

It lights up directly and went dimmer when we cover the photocell

Sources of Error:

1. Led is set up backward
2.We assign negative current on Waveform power supply

Second Trial :

 Overall Layout of the Circuit Connected to Voltage Scope on Waveform.

Scope

 Voltage across Photocell (dark)

Voltage across Photocell (light)

Summary:
Equivalent Resistance of resistor in series is equal to the sum of Resistance of all resistor. Equivalent Resistance of Resistor in Parallel is equal to the inverse of  the inverse sum..  The Resistance of Photocell increases when the light intensity goes down, increasing the current flowing through it. Higher value of current increases the potential difference between photocell. High Potential difference between photocell results in anode light up brightly.  

Week 1 Day 2

Lecture 

Topology Problem, branches  is equal to number of loop and nodes subtracted by one

Another Kirchoff problem :(

Resistors and Ohm's Law Lab.

The overall look of the circuit when we measure the voltage and resistance, in this set up we place our DMM in parallel with the resistor:

A closer look at how we measure the resistance of resistor:

Resistor have a value of 100 ohm

Circuit set up on measuring current, in this set up we put our DMM in series with the resistor

We measured and recorded the value of current in different voltage:

Sketching the current versus voltage. we can see that the voltage have a linear relationship with current 

MOSFET Lab

Set up of voltage gate in Waveform software. here we set our current to be a DC current with value ranges from 1V to 5 V

The overall look of our MOSFET circuit set up:

Closer look of our set up, the alligator clips are connected to DMM and placed in series with the 100 Ohm resistor

We recorded  the value of current for different value of voltage gate

The graph of current versus voltage gate. The current and voltage shows a linear relationship between 1.5 V to 2 V and levels up to 5 V

Summary:

In a simple resistor-independent voltage source, the current is directly proportional to the voltage.
V=IR, where V represent voltage, I represent current, and R represents resistance. MOSFET acted as Voltage Controlled Current Source. The bigger the voltage gate the bigger the current flows to the circuit. when the value of voltage gate is greater than 3V, the current levels up to 50 mA (The MOSFET transistor have zero resistance)

MatLab

FreeMat Packet

Using FreeMat as Calculator

Math Function

Assigning Expressions to variables

Creating matrix

Creating row vector

Applying Function to row vectors:

Plotting Exponential and sinusoidal

Operation with Complex Numbers

Function to convert from rectangular to polar:
Excercise 1

Excercise 2

Assignment 1

Summary
You can use matlab to do various task that you can do in your calculator faster. We can use its matrix function as a great tool to solve complex circuit that have multiple meshes and node. We can also uses matlab command to solve for roots of a polynomial equation. We can also uses matlab to graph our model using plot command.