March 17

Time-varying Signals
In this lab, we learned how to use the arbitrary waveform generator to generate time-varying signals and use an oscilloscope to measure the signals.

The picture shows how the circuit was connected. We set that R1=R2, so we predicted that Vout is 1/2 Vin for all 3 different waveforms.

This is a picture of the circuit. 

This is the input waveform for the sin wave. Vmax = 2V.

This is the output waveform for the sin wave. Vmax =1V.

This is the output waveform for the square wave.

This is the output waveform for the triangle wave.

All the output waveforms have  their maximum voltage output as 1/2 the input.

A BJT Curve Tracer.

The purpose of this lab is to investigate the collector current vs collector voltage of the BJT. 

This is the schematic circuit diagram.

 We plot channel 1(Vce) on the X axis, and channel 2 (Ic) on the y axis. Current Ic can be obtained from dividing C2/100 ohm
There is a linear region in between the threshold voltage and saturated voltage.

March 19

Thevenin Example using EveryCircuit

Thevenin Equivalent
In this lab, we learned how to use Thevenin Equivalent to simplify a complex circuit to a simple circuit with one Voltage supply and one resistor.

After calculation, we found Rth = 7.2kohm and Vth = 0.4579V for the terminal a and b.

This is how the circuit was connected.

 We chose an 1kohm resistor and a 10kohm resistor as RL.
V1k = 56mV and V10k = 269.2mV.

The actual value of Vth = 0.460V and Rth = 7.17kohm.

We used a potentiometer as RL.

This is how Rl(kohm)VS. V(mV) looks like.
And Rl VS. Power is linear with a constant slope.

The Thevenin equivalent circuit helps simplify a complex circuit into a simple circuit so we don't have to recalculate the whole circuit when only one circuit element is changed.

March 24th

Non-Ideal Power Sources
In this lab, we experienced the structure of a non-ideal voltage supply, and how it affects the circuit.

In the pre-lab, we calculated the power outputs for an ideal voltage supply at 1V connected to a 22 ohm resistor, and the power outputs for a non-ideal voltage supply at 1V connected to a 22ohm resistor.

We measured the power output of a non-ideal voltage supply with three different resistors. The internal resistance is not a constant number. This indicates that the voltage supply contain a more complicated circuit than an single resistor.

Maximum Power Transfer.

In this lab, we learned the maximum power delivered to a load is when the load resistance is equal to the Thevenin Resistance.

We connected the circuit as shown in the picture and calculated the theoretical maximum output is 2.84mV.

This is how the circuit is connected. We measured the power output of the second resistor.

After the measurement, we found that the true power output was also 2.84mV which agree with the theoretical maximum power output we calculated before.

March 26th

Inverting Voltage Amplifier
In this lab, we used a single operational amplifier (OP27) to implement the process of multiplication by a negative constant.

We used the equation Vout = -R2/R1 * Vin to get that R2/R1 should be around 2 to provide a gain of double the voltage. Then we used R1 = 1.8k ohm, and R2 = 3.6k ohm because they are the standard resistors and R2/R1 is 2.

This is how the circuit was connected.

This is a Vin/Vout table of the circuit. Vout/Vin is about -2

In the picture, we can see there are limits on how much Vout can output. In theory, the upper and lower limit should be +/- 5V. But really, the upper limit is 4.18 and the lower limit is -3.38. This was caused there is no perfect op-amp. Better op-amp can have its limit close to the rail voltages.

March 12

Quiz

Mesh Analysis III
In this lab, we learned how to use mesh analysis to predict a circuit's behavior.

 We used mesh analysis to find the current I1 and the voltage V1

 We built the circuit with the four resistors shown in the picture.

 This is how the circuit looks like.

After measuring, the actuarial I1 = 0.254mA, and V1 is 2.44V. The numbers agree with the predicted value we calculated before.

Mesh Analysis is one way to simplify a complex circuit so we can find the characteristic of the circuit easier.

March 10

Nodal Analysis
In this lab, we learned how to use nodal analysis to predict circuit behavior prior to building and testing a circuit.

For the circuit shown in the picture, we used nodal analysis to find that V1=4.42V and V2= 2.42V.

This is a picture of the actual circuit.

We measured and found that Vx= 2.41V and Vy = 4.39V

The nodal analysis is an useful tool to analyze a circuit and to find its characteristic.

March 6 Temperature Measurement System

Quiz

Temperature Measurement System

In this lab, we used a thermistor, a resistor with resistance depends on temperature, to design a cirtuit.

This is a diagram of the circuit. In order to have a 0.5V voltage difference output. We calculated that we should use a resistor Rth around 10k ohm.

This is a picture of an actual circuit.

This is another picture of the circuit.

With the 10kohm resistor, this is the minimum voltage output.

With the 10kohm resistor, this is the maximum voltage output.

March 3 Dusk-to Dawn Light

Dusk-to-Dawn Light

In this lab, we created a light sensing system by using a BJT photocell, and the concept of voltage divider. The circuit operates as a 'dusk-to-dawn' light.

This is the circuit diagram.

After calculation, we found the expected output voltage Vb is 1.67V when R is 5kohm and Vb is 3.33V when R is 20kohm.

This is a picture of the actual circuit.

The circuit is working. When the light sensor is covered, the LED light on.

Feb 26 Ohms Law and MOSFETs

Resistors and Ohms Law
In this lab, we measure several combinations of voltage and current through a resistor.

We connect a 100 ohm resister to the power supply at 3V.

Table of Voltage VS. Current through a resister of 100 ohm

I(mA)= 9.0395(V) + 0.0395 R^2 = 0.999999

There is a linear relationship between voltage and current through a resistor.

Dependent Sources and MOSFETs
In this lab, we explore the characteristics of a MOSFETs by measuring the gate-opening voltage.

This is a picture of the connected circuit.

At V = 1.80V, the gate opened and current can flow through the MOSFET from the drain to the source.

FreeMat Assignment

Assignment 1

Plotting
Assignment 1
2e^-t/tau

Circuit A will have the lowest output sooner.

2*(1-e^-t/tau)

Assignment 2

3sin(2t + 10degree) + 5 cos(2t-30degree)

To increase the frequencies, we would have to modify the number inside sin() and cos().

Complex number 

Assignment 1

Assignment 2

Assignment3

Assignment 4

Finding roots