Thursday, February 4, 2016

Week 4

Blog sheet week 4

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). The circuit should look like below:


According to our table, our graph will be an exponential relationship between Ic and VBE. Ic is determined by the value of VBE 

Table 1: Relationship between VBE and IC

VBE
IC
0V
0.0004 mA
0.23V
0.0005 mA
0.5V
0.0008 mA
0.6V
0.036 mA
0.62V
0.07 mA
0.81V
13.42 mA




Graph:
Graph 1:  Ivs VBE 

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 circuit should look like below:




 According to our table, the relationship between Ic and VBE stays the same. However, with VCE involved, it doesn’t affect the outcome of Ic. Instead of an exponential line, the result contains multiple horizontal lines.

Table 2: Relationship between VBE and Ic with VCE
VCE
VBE
Ic
0
0V
0 mA
1V
0.2V
0 mA
2V
0.7V
22.2 mA
2V
0.8V
35.6 mA


Graph:

Graph 2: Ivs  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?

a

Table 3: Relationship between IC and IB with VCE and VBE
VBE
VCE
Ic
IB
0.7 V
2 V
38.1 mA
0.037 mA
0.75 V
2 V
49.1 mA
0.655 mA
0.8 V
2 V
49.2 mA
1.47 mA

Ic and IB are related by being a ratio equally to current gain, where current gained doesn't change if the voltage value changes. It was a little difficult trying to read the current measurements because the readings were jumping all over the place. Our data for the most part supports our theory since our values for Ic were fairly close.
IC/IB= β

                 

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



Table 4: Different light sources with photocell resistance
Light Setting
Photocell Resistance
No light
17.1 kΩ
Room light
2.5 kΩ
Flashlight (iPhone)
40 Ω

As you can see, the darker it is, the more resistance there is of 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.


      Table 5: Different voltages applied to the DC motor with current measurements
Voltage Applied
DC Motor Current
0 V
0 mA
1 V
26 mA
2 V
31.2 mA
3 V
34.4 mA
4 V
37.3 mA
5 V
39 mA

According to our table, the higher the voltage, the higher the DC motor current. This supports Ohm's Law, where voltage and current are directly related.



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.


Table 6: Same voltage is applied to the DC motor, but the second measurement has an increased load on the motor
Voltage
Current Measured
2 V
30.1 mA
2 V (pinched)
57.5 mA


When the motor was pinched, the current measurement increased; the amount of pressure on the motor determines how much current there is. If you were to slightly pinch it, there shouldn't be that much of a change of the current value. Pinching the motor harder would cause the motor to have a greater amount of current flowing through it than the 57.5 mA we've measured above.


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



Video 1: Operation of the circuit



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’s role is to limit the voltage and current going into the collector.

  • When R4 is smaller (47 Ω), the DC motor will spin. The voltage at the collector of the transistor is 9.44 V and the current at the collector is 29.2 mA
  • When R4 is larger (1 ), the DC motor won’t do anything. The voltage at the collector of the transistor is about 4 V and the current at the collector is 3.0 mA

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

    
       In our Rube Goldberg setup, the DC motor acts as a pulley, raising an object (in this test run, a paper flag). The DC motor would spin if there is a light source hitting the photosensor, and wouldn't spin if there's no light source.


Video 2: Test run of our Rube Goldberg setup













9 comments:

  1. I like how you made a graph for question 6 instead of just an explanation.

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  2. I thought your explanation of R4's role in the circuit was fairly descriptive. We ended up going into more detain after reading your response.

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  3. This comment has been removed by the author.

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  4. For number 6 I think there should be more explanation. Why does the voltage rise when it's pinched? Or at least why do you think? Everything else looks solid.

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  5. This comment has been removed by the author.

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  6. The explanation of circuit 7 was very well done.

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  7. Good job. Next time, plot your graphs using Excel or Matlab.

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  8. I like the way you implemented the motor in your Rube Goldberg setup! That could have a lot of applications I think.

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