Lab 4

Blog Sheet Week 4

1.  (Table and Graph)  Use the transistor by itself.  The goal is to create a graph for Ic (y-axis) versus Vbe (x-axis).  Connect base to collector.  Use 10k potentiometer to generate voltage.  Use 5v but DO NOT EXCEED 1V 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 points to do a graph.  (Suggestion:  measure Vbe = 0v, .5v, 1v and fill the gaps if nessesary by taking extra measurements)  The circuit should look like below:

Question 1
Measured Voltage	Measured Current
.1 mV	0 mA
.298 V	0 mA
.425 V	0 mA
.51 V	0 mA
.59 V	.019 mA
.621 V	.069 mA
.64 V	.246 mA

This table shows the measured voltage (Vbe) and the measured current for Ic.

This is a chart showing the relationship between Ic and Vbe.  Vbe is the x-axis and Ic is the y-axis.

2.  (Table and Graph)  Create a graph for Ic (y-axis) versus Vce (x-axis).  Vary Vce from 0V to 5V.  Do this measurement for 3 different Vbe values:  0V, .7V, .8V.  The circuit should look like below:

Question 2
Measured Voltage (Vbe)	Measured Voltage (Vce)	Measured Current (Ic)
0V	0V	0mA
0V	2.5V	0mA
0V	5V	0mA
.4V	0V	0mA
.4V	2.5V	0mA
.4V	5V	0mA
.57V	0V	0mA
.57V	2.5V	.02mA
.57V	5V	.019mA
.69V	0V	.718mA
.69V	2.5V	3.8mA
.69V	5V	4.03mA
.83V	0V	1.19mA
.83V	2.5V	OL
.83V	5V	OL

This table shows the voltage for Vbe, Vce, and the current for Ic.

This is a graph of the collector current (Ic y-axis) versus the voltage of the emitter (Vce x-axis)  As you can see when the base has 0V we get no reaction from the transistor.

This is a graph showing the collector current (Ic y-axis) versus the voltage of the emitter (Vce x-axis) while the base voltage is at .69V 

This is a graph of the collector current (Ic y-axis) versus the voltage of the emitter (Vce x-axis) as while the voltage of the base is at .83V.

3. (Table)  Apply the following bias voltages and fill out the table.  How are Ic and Ib related?  Does your data support your theory?

VBE	VCE	IC	IB
0.7 V	2 V	.29 mA	.7 mA
0.75 V	2 V	.51 mA	1.65 mA
0.8 V	2 V	.95 mA	3.5 mA

The relationship for Ic and Ib is that Ic/Ib = beta.  The ratio should be nearly the same for all measurements taken.  For our three measurements our betas were .41(7V), .30(7.5V), and .27(.8V).  While the ratio is not exactly the same for each Vbe it does not stray too much from the average (.327)

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

A photocell is a light dependent resistor.  Resistance of the cell is high when unilluminated while the resistance is low when fully illuminated. 

Question 4
Light Condition	Photocell Resistance
No Light	8.2 kΩ
Partial Light	3.4 kΩ
Room Light	1.03 kΩ
Flash Light	84 Ω

This table shows the resistance of the photocell resistor compared to the light allowed to hit the cells.

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

Question 5
Voltage (V)	Current (mA)
0	0
1	33.5
2	41.2
3	46.7
4	51.9
5	53

This table shows the voltage applied to the DC motor and the current measured going through it.

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

Applying 2 volts to the DC motor gets us 38.9 mA of current with no additional resistance applied.  As we apply resistance with our fingers to the shaft of the DC motor the current increases based on how much pressure we are applying.  For example, squeezing as hard as we can we get a current 156.9 mA.  Slight pinching the motor gets us about 110 mA of current.

7.  (Video)  Create the circuit below (same circuit from week 1) and explain the operation in detail.

A video showing the operation of the circuit above with an explanation.

8.  Explain R4's role by changing its value from a smaller resistance to a higher resistance.  Observe the current and voltage as you change the resistance.

Question 8
Resistance	Current	Voltage
47 ohms	40.5 mA	1.83V
120 ohms	37.8 mA	4.35V
10 ohms	39.6 mA	394.5 mV

A graph showing the resistances we use along with the measurements we obtained.

The role of R4 is to limit the current and voltage coming into the collector.  The higher the resistance the lower the current flowing into the collector. 

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

In our Rube Goldberg set up we used the motor, attached to a wire, to pull a short piece of wire to complete a circuit between a power supply and a LED light.  The idea is that the motor will pull on the wire, completing the circuit and turning the LED light on.

A video showing our first attempt to complete the LED circuit using the motor to pull a wire.  We did not cover up the photocell resistor and the motor pulled the wire past the LED connection.

A video showing the completion of the LED circuit by using the motor to pull a wire connecting the LED to the power.