Wednesday, February 1, 2017

Blog 4 Group 1

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. 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).
Ic (mA) VBE (V)
0 0
0 0.25
0.01 0.5
0.2 0.7
116 0.8
122 0.9
Table 1: Shows relationship between Ic Vs. Vbe 
Graph 1: Shows relationship IC vs. 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.
Vce (V) Ic (mA) VBE= 0V Ic (mA) VBE=.7V Ic (mA) VBE=.8V
0.5 0 17 57
1 0 33 99
1.5 0 53 108
2 0 74 128
2.5 0 98 154
3 0 130 179
3.5 0 154 220
4 0 179 248
4.5 0 211 303
5 0 246 343
Table 2: Shows relationship between Ic Vs. Vce
Graph 2:Shows relationship between IC vs 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?
VBE (V) VCE (V) IC (mA) IB (mA)
0.7 2 78 0.07
0.75 2 104 10.4
0.8 2 142 12.5
Table 3: Shows how Ic and Ib are related
As Ic increases so does Ib.  The value of Ib starts so low because the transistor did not begin to allow current until .7 volts.  But as soon as it passed that value they both increase at a steady rate.

4. (Table) Explain photocell outputs with different light settings. Create a table for the light conditions and photocell resistance.
Photocell light setting will change drastically with different amounts of light.  The higher the amount of light, the higher the output should be, which also means less amount of resistance. 

Light: Resistance:
No light 12 k
Room light 1.3 kΩ
Flash light 100 Ω
Table 4: Shows the resistance with different amounts of light

5. (Table) Apply voltage (0 to 5 V with 1 V steps) to DC motor directly and measure the current using the DMM.
Motor (V) Current (mA)
0 7.9
1 26
2 33.4
3 38.7
4 43.5
5 47.3
Table 5: Shows the current through the DC motor at different voltages

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.
Motor (2V) Current (mA)
No load 33.1
Light load 120
Medium load 130
Heavy load 150
No spin 160
Table 6: Shows how increased load changes the current
As you increased the amount of load on the motor, the amount of tension increased causing the current to increase.

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

Video 1: Shows the circuit and how the amount light powers the photocell
Explanation in the video.

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.
As R4 changes, so does the current.  If R4 becomes a stronger resistor, then the current will go down. If R4 decreases in strength, then the current increases.  Since resistance and current are inversely proportionate, this makes sense. 

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

This is the start to our Rube Goldberg circuit.  The way its supposed to work is that when the motor is activated the the gears will begin to turn which turns the belt and begins to lift up the platform where the photocell is hidden in the dark, once exposed the photocell should have less resistance which turns on the diode.  Unfortunately we were unable to locate a working diode.  It is a work in progress but has a lot of promise for the rest of the semester.


  1. Just a couple comments on your figures. I'd suggest adding axis titles to your first graph and make sure your V_BE is not being plotted on the current values (orange line). Also with all of your tables, the color scheme is making it so your values can not be read on the grey lines, as the text and the highlighting are matching.

    1. Thank you for the help with formatting!

  2. This comment has been removed by the author.

  3. I suggest you to change some colors in your blog specially in the tables because there is some numbers we cannot read them. I tried to compare our calculation with yours and I found that all calculations are mostly same with small differences in digits which do not make and wrong in calculations.
    Good job!

    1. Thank you for the help with formatting! I wonder where the small error between our calculations comes from.

  4. Love the concept behind the rube goldberg system! You might want to switch out the current gear for a bigger one to prevent it from slipping.
    I was looking at your data. The first graph you posted. the Ic vs Vbe. Your table looks good. It shows that the current is amplified after .7 volts. However, I think it would be good if you took for values to show that on the chart, just for a visual purposes.

    1. Yes you are probably right the conclusion we have both drawn from the data may not be so clear to someone who has not completed the lab.

  5. I like the way you guys set up your blog its easy to follow. I also like how you guys color coded your first graph so I knew what was happening. I also like your idea for your Rube Goldberg project. Good luck with it!

  6. If you guys are using Excel to make your graphs, I would suggest using 'exponential' or 'polynomial' to make your line of best fit. If you google 'VBE vs IC' or 'VCE vs IC' graphs you will see that it is a curved line. It looks like you two are using the linear option which is actually quite inaccurate because as your base-emitter voltage approach .7 V, your collector current goes up exponentially with even a marginal increase of the voltage. I can show you how to do this in class if you like.

    1. Thanks Nick! Yes, I had not noticed that but you seem to be exactly right about us using a linear fit for our data we will look into that.

  7. We ended up getting our resistance to 30 kilo-ohms with the light off!! We had to completely cover it up with our hands. I thought that the resistance would go up with the light but it ends up going down. Also I really liked watching your Rube Goldberg set up!! It was a great idea. We just did a simple one, we had the motor drag a tennis ball up a ramp. Also is it just me or was the circuit easier to build this week than it was on week 1? Now that we are used to the class and circuit board and everything!