Thevenin Equivalents, March 28, 2011

The purpose of this lab is to develop a circuit that uses idea of Thevenin to practice Thevenin Equivalent calculation. The circuit is formed by 2 voltage source 4 resistor and 1 load resistor. First we calculated the Rth=66 ohm and In=131mA and Vth=8.64V.  Then we set up the simple Thevenin circuit to test our answer. The reading on multimeter is Rth=67.4, Vth=9.07. After that we put the load resistor into the circuit and run it. When load is 821 ohm, the voltage across the laod is 8.87 V. Then we set up the complex circuit and run it. Unluckily, our resistor cannot hold the current, and it started to burn out. Therefore, part 2 isn't doable.

PSpice, March 23rd

For today's lab, we learned how to use PSpice to analyze our circuit voltage and current. The PSpice program is so convince to help on circuit. The first circuit shown in the picture is from the PSpice tutorial. We learned how to open up the program, add wire, voltage source, current source, and resistor. We also learn how to change the value of those things and run the circuit. It is so easy to analyze with PSpice. The second circuit is one of our hw problem. We used to do a lot of calculation to do this one, but with PSpice, it is a piece of cake.

March 14, Nodal Analysis

The purpose of this lab is to develop a circuit to testify if our calculation using nodal analysis is correct. We have 3 resistors represent cable which are 100ohm, and 2 220ohm in series, and 2 1k ohm resistors in parallel. Then we have a 12V battery source from left, and a 9V battery source from right. Then we use our nodal analysis to calculate what current values are going through each battery and power rating of the battery. Then we run the circuit and measure the current and voltage through the battery source. We find:
                              I(1)=17.4mA             I(2)=1.33mA
                              P(1)=210.54mW       P(2)=11.97mW
The value is really close to what we calculated. 

March 9, Voltage Dividers

The purpose of this lab is to design a battery source and a resistor at the beginning of the circuit to make 3 parallel loads work when different switch is on. First we use 3 1k ohm resistor to represent the 3 loads and put them in parallel. Then we calculated that the maxium of Req of three loads is 1000ohm and the minimum is 333ohm. Then we solved for voltage across the battery and the resistance of the resistor at the beginning of the circuit. In the picture, the yellow resistance box is our beginning resistor. we set it up to 55 ohm. then we connect everything through breadboard. We put voltmeter and current meter into the circuit and measure the Req, voltage across the loads and current. We found out because our battery source doesn't have 5.5V, so we used a 6.12V.
1 load: 999ohm            2 loads: 498 ohm                3 loads: 333ohm
V= 5.77V                    V=5.46V                            V=5.18V
I=5.7mA                       I=10.7mA                          I=15.1mA

March 7, 2011. Introduction to biasing

The purpose of this lab is to decide how to build up a circuit that a 5V LED and 3V LED will glow and not blow up. First, we built a parallel circuit for both LEDs. However, only putting the LEDs in the circuit is not good enough. The LED will blow up quickly as we turn the battery source on. Therefore, we put a resistor in front of each LED to reduce current through them. Then we insert a current meter between the LED and 1 resistor and a voltmeter across 1 of the LED to test the current and voltage. Finally, we could use calculation to find the best resistor to fit in the circuit and not make the LED to blow up, and choose the one from the reality that we are possible to use.

R for 5V LED = 150 ohm
R for 3V LED = 360 ohm
Efficiency: 41.6%

This is the picture of a blown up LED

March 2, 2011 Lab 1

The purpose of this lab is to determine how long the cable that separates the battery source and load can be. In the image, the white box is our battery supply. The tiny thing in the middle is our load which has a resistance of about 1000 ohm. The yellow box is a resistor box which represents our cable line. The multimeter on the left is a voltage meter that checks the voltage across load resistor. The multimeter on the right is a current meter across the circuit. The way we do it is to set the battery to 12V and keep increasing the resistance of the resistor box to get the minimum voltage that load still can work. Then we have the maximum number of the resistance of the cable. Therefore, we are able to determine how long a cable line could be.