Monday, January 30, 2017

Week 4


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).

                                                                      Figure 1:  VBE and Ic
        Figure 2: Voltage vs. Current  

  • The circuit presented in Figure 1 of the worksheet was built on the breadboard. We then added different voltage values all of them below one, in order to see the relationship between VBE and IC. The data means that there is a certain voltage (VBE) required before Ic can flow.                                    

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. 

Figure 3: IC vs VCE

Figure 4: Table of data graphed in figure 3.
  • We built a circuit as the one in problem one, this time with two different voltage values. We performed three different trials with different voltage values for each one. We started off with an initial voltage of zero, which gave us 0 current independently from the second voltage added to it. We then bumped the voltage to 0.7, which gave us an increasing current value dependent on the second voltage added. On trial number 3 the results were similar to trial number 2, just a little bit higher since we bumped up the initial voltage from 0.7 to 0.8. The data is interpreted as Ic being dependent on VCE which are both dependent on VBE. 

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

Figure 5: Table displaying data of relationship between IC and IB

  • Our theory on the relationship between IC and IB is that they should be always have a constant ratio no matter what the value, this ratio is known as beta. The ratios for the first 2 trials are the same but for the third trial it is not the same. An error could have occurred within our circuit or while measuring to produce this difference.
4.) (Table) Explain photocell outputs with different light settings. Create a table for the light conditions and photocell resistance.

Figure 6: Table showing properties of photocell
  • From the results we acquired from the table above we can clearly see that resistance increases as light decreases, and it decreases when the light is more intense.

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

Figure 7: Table of voltage applied to motor and current through motor
  • The data in the table displays that as the voltage applied to the motor increases, so does the current.

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 voltage of 2.01 was applied to the DC motor the current demanded with no load was 32 mA. As we applied more pressure to the shaft the current kept increasing, maxing out at 150 mA when the motor completely stops.
7.) (Video) Create the circuit below (same circuit from week 1). Explain the operation in detail.

Figure 8: Picture depiction of the circuit created in the video.

Figure 9: Video explaining 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.
  • If R4 was changed to a bigger resistor the speed of the motor will go down. If R4 is changed to a smaller resistor, the speed of the motor will go up.
9.) (Video) Create your own Rube Goldberg setup
Figure 10: A video displaying our Rube Goldberg circuit.

  • Our Rube Goldberg uses the circuit above but with a different motor. It works quite well but still needs some tweaks to work better.


  1. I like your graphs and tables, very clean and easy to read. I think your tables need captions under them to help the reader understand your tables and graphs.

    1. Thank you for the comment. Im glad the data is easy to interpret.

  2. For Question 1, Our graph plot ended up curving upward much sooner than your graph did and I noticed that an almost similar value for VBE was substantially higher than yours, I think it must have been due to the transistor because of the essentially same circuit set up.

    1. Thats interesting how your number one increased much sooner. I agree that it must have been the transistor or possibly could have been due to different lighting for the photo sensor? Anyways thanks for the comments!

  3. I found it interesting that in question 5 between 3 and 4 volts the current exhibited no apparent change; do you have any thoughts on what caused this? Also, what are your thoughts on the relationship between IC and IB in question 3?

    1. I not really sure why there was no change in current between 3 and 4 volts, thats a good question. Also my thoughts on the relationship between IC and IB is that its dependent on beta which is further explained in the question now. Thanks for the comments!

  4. The first table and graph are really nice and clear for me. We struggled doing that one we had to go over 5 values measurement to make it clear. However, for question number 2 we did more values and measurements and did not get a straight line like yours. Do you thing if you did measure more values for Ic and VCE you will still get a straight line?