Week 4, 2/1-2/5:

1.(Table and graph) Use the transistor by itself. The goal is to create the graph for IC (y axis) versus VBE (x axis). Connect base and collector. Use 10K potentiometer to generate the voltage. Use 5 V but DO NOT EXCEED 1 V for VBE. Make sure you have the required voltage value set before applying it to the base. Transistor might get really hot. Do not TOUCH THE TRANSISTOR! Make sure to get enough data points to graph. (Suggestion: measure for VBE = 0V, 0.5V, and 1V and fill the gaps if necessary by taking extra measurements).

This was the circuit given for us to build.

Pictured above is the circuit that we built.

Vbe (V)	Ic (mA)
0	0
.518	.0035
.652	2.22
.707	31.78
.962	119.50

The table above contains the voltage values for BE and current for C.

This line graph displays our data.

2. (Table and graph) Create the graph for IC (y axis) versus VCE (x axis). Vary VCE from 0 V to 5 V. Do this measurement for 3 different VBE values: 0V, 0.7V, and 0.8V. 

The picture above is what the circuit should look like.

The picture above is the circuit that we built.

Vce (V)	Vbe (V)	Ic (mA)
.985	0	0
.985	.707	2.9
.985	.795	39.2

This chart is when Vce is at nearly 1V.

Vce (V)	Vbe (V)	Ic (mA)
3.05	0	0
3.05	.702	3.3
3.05	.795	73.9

This chart is when Vce is at nearly 3V.

Vce (V)	Vbe (V)	Ic (mA)
4.98	0	0
4.98	.695	5.7
4.98	.796	198.5

This chart is when Vce is at nearly 5V.

This graph compares Ic versus the different values of Vce.

 

3. (Table) Apply the following bias voltages and fill out the table. How is IC and IB related? Does your data support your theory? 

Ic and Ib are related by beta. Beta is calculated by dividing Ic by Ib.Our data supports the theory because as IC increases, IB increased by a nearly proportional amount

VBE (V)	VCE (V)	IC (mA)	IB (mA)
.710	2.00	5.26	.034
.753	2.00	15.6	.106
.796	2.00	50.26	.364

The table above contains our results from measuring the voltages and currents of the transistor.

4. (Table) Explain photocell outputs with different light settings. Create a table for the light conditions and photocell resistance.

The photocell increases in resistance as light decreases. The more light that is on the photocell the more resistance the photocell will provide. The less light, the less resistance. A table of our observations is below. For limited light we covered the cell. For normal light we did not change the light. For increased light we used a flashlight on the cell.

Status	Resistance (kilo ohms)
Limited light	11.5
Normal light	2.56
Increased light	.370

The table above contains our measurements for resistance on the photocell.

5. (Table) Apply voltage (0 to 5 V with 1 V steps) to DC motor directly and measure the current using the DMM.

Voltage (V)	Current (mA)
0	0
.97	25.9
2.06	33.3
2.95	38.7
4.07	45.3
4.95	49.7

The table above contains our measurements for voltage and current applied directly to the DC motor.

6. Apply 2 V to the DC motor and measure the current. Repeat this by increasing the load on the DC motor. Slightly pinching the shaft would do the trick. 

A table below shows our data from measuring the motor. 2.06 V were applied for the test. Our load was slightly pinching the shaft of the motor.

Status	Current (mA)
No Load	33.4
With Load	85.3

The table above contains our observed current values when changing the load on the motor.

7. (Video) Create the circuit below  (same circuit from week 1). Explain the operation in detail.
when we covered the photo sensor, the value of it is big. Because of voltage divide, the voltage across resistor (R6=1k) is really small. So Ib small lead the current go through the DC motor small. In this conditon, motor goes slowly. when we light the photo sensor, the voltage of R6 increased. Ib increased cause Ic increased. Motor turns faster.

This is the circuit that we had to construct.

The video above describes the circuit that we constructed.

8. Explain R4’s role by changing its value to a smaller and bigger resistors and observing the voltage and the current at the collector of the transistor. 

R4 limits the amount of current the motor gets. With a stronger resistor the motor will turn at a slower rate. With a smaller resistor the motor will turn faster. A table of our observations is below. Actually, when we short R4 is unreasonable, it might burn the transistor. However, we could not find a resistance smaller than 47. Two resistance in parallel can create a smaller one but we did not remember at that time.

Resistor (Ohms)	Voltage (Volts)	Current (mA)
0 (short circuit)	0	32.3
47 (original size)	1.6	28.75
310	9.50	24.3

The table above compares the differences in current and voltage based on resistor size.

9. (Video) Create your own Rube Goldberg setup.

For our Rube Goldberg set up we will have the motor pull a string attached to a mouse trap. The mouse trap will be dragged into the circuit and will activate to send a ping pong ball flying in a general direction. A video of it is below.

The video above shows our Rube Goldberg machine in action.