Monday, January 30, 2017

Daniel Bruce and Moaad Alzahrani
Blog sheet week 4
(January 30 - February 3)

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). 

Table 1.1 Voltage of Base Emitter and the current flow through the collector

Graph 1.1 Shows relationship Vbe vs Ic

The graph above shows that the current of the collector is dependent on the voltage of the base emitter; also note that there is almost no current flow until the voltage of the base emitter reaches about .7 volts. This point of current flow is known as saturation.
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.



Table 2.1 Voltage base emitter and collector and corresponding current of collector



Graph 2.1 Shows the Vce vs Ic relationship in a transistor from our experiment

The graph above shows that the current in the collector increases rapidly with an increase in voltage of the collector. But the graph also shows that the base emitter requires around .7 or .8 Volts to achieve this increase in the collector. It should also be noted that when we applied .8 volts to the base emitter the transistor was behaving abnormally and was giving us unusually low readings of current through the collector. We later found that the transistor was faulty in our experiments; and we did not have enough time to repeat the experiment to get new readings, but it is still useful in showing the relationship of increase in Vc results in increase of Ic.

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 V
2 V
138
.152
0.75 V
2 V
276
.281
0.8 V
2 V
385
1.12

Table 3.1 Changing base emitter voltage and measuring corresponding collector and base current

From our measurements we see a trend of the current through the base is much smaller than the current through the collector. Around .7 Volts we see a significant amount of current flow. As the voltage is increased in the base emitter the amount of current flow through the collector begins to become excessive causing heat build up in the transistor.
4.       (Table) Explain photocell outputs with different light settings. Create a table for the light conditions and photocell resistance.


Table 4.1 Shows resistance values of photo cell as varying degrees of light

When there is no light on the photocell the resistance increases to the maximum amount. As we increased the amount of light on the photocell, the resistance seemed to dropped quite a bit giving a range of about .3K ohms to 12K ohms.

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


Table 5.1 Shows voltage values and corresponding current values through the dc motor

We saw that increasing the voltage on the dc motor caused the current flow to increase as well  as increase the rotational speed of the 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. 

When we applied 2V to the motor and let it spin freely it consumed about 32.9 mA, when we pinched the shaft on the motor the current rose to 161 mA.

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


.

Video 7.1 Explains the operation of the circuit below we constructed

We showed how the transistor, motor and photocell are able to work together and be activated by light to provide current to the transistor; which then allows current to flow to the motor.





  Circuit Diagram 7.1 Electrical circuit with transistor,motor and photocell


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. 

Resistor 4's role is to limit the amount of current that flows through the motor. When we put a resistor of higher value  the motor would barely spin even with light shining on it. We also put a wire in place of the resistor (very low resitance value); this caused the motor to spin faster.

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


Video 9.1 Demonstration of our Rube Goldberg circuit

The video shows the 3 major components (transistor, motor, and photocell) we learned about this week working in unison to create a Rube Goldberg.

17 comments:

  1. For Question 4, Our measured photocell resistance for the changing light source was quite different from your values, which would make sense why our values for the tables requireing the photocell differ so much compared to yours.

    ReplyDelete
    Replies
    1. I think it make sense to have different values due to the different flash we point to the photocell or due to the light where we are sitting.
      Thanks.

      Delete
  2. i think you are just missing the graph and the explanition for questions # 1 and 2, Also, i have noticed that we get the same vale for the resistor in question #4 when we used the flash light both of us get 0.3 k ohm.

    ReplyDelete
    Replies
    1. We did add the graph after your comment.
      Thank you.

      Delete
  3. Why do you think the applied load to the motor effected the current values measured? Also, my group's values for IB in question 3 differed from yours by roughly a factor of 10, but we noticed a similar relationship between IB and IC, what are your thoughts on the reason for the large difference between IC and IB for this table?

    ReplyDelete
    Replies
    1. We did get different readings for the same question sometime, and as we were told that bending the transistor will damage it which might cause the different readings. Also, we did have some issues adjusting the voltage values. I think as we noticed the same relationship, we are in the right track.
      Thanks.

      Delete
  4. For question #1 your values for Vbe and IC were much lower than ours, do you have any ideas why? Also i liked your Rube Goldberg design and considering you're the group right before us i think our projects will fit together well! Good job

    ReplyDelete
    Replies
    1. We are not sure what cause the that, but as we can see each group had different values. We think it could be because of the transistors or sitting the voltage values. Bending the transistor will damage it as we did the first time, and we faced some difficulties adjusting the voltage values as well which we think these could be the cause of the different readings.
      Thanks.

      Delete
  5. For the values, we related on a lot. For the most part everything we have is consistent. Did you have any issues on anything? We had a couple issues in the original set up with the transistors. But once we figured out the correct set up for the resistors and wires it was easy to do. Good job!

    ReplyDelete
    Replies
    1. We did bend the transistor which cause us some issues. After figuring out this with Kaya's help, we change the transistor and everything worked well after that.
      Thanks.

      Delete
  6. I really liked your Rube Goldberg set up. Ours was a little more simpler but yours was really cool. Also we ended up getting 30 Kilo-ohms for our resistance with no light. On #5 our current values were very similar as well!! Our IC vs IBE graph was a little different because our voltage didn't end up leveling out at the end it just kept going up. Maybe we didn't take enough measurements but we will try to get it to level off next time since multiple groups have reported it!

    ReplyDelete
    Replies
    1. We think the different values in question #4 due to the different flash light that we point to the photocell or due to the moderate light where we were sitting. We did have hard time adjusting the voltage as well. We were told to take measurement as much to make it clear and to see that we are on the right track. So, maybe it is your issue.

      Delete
  7. Your graphs look great, for question #2 i understand the titles are the only thing different, but you could use 1 graph and make it look less crowded on the page. Our data was much similar with yours, showing the exponential curve is important because it helps to explain transistors relationships with a circuit. Your Rube Goldberg was creative, its cool seeing how everyone's came together through our blogs.

    ReplyDelete
    Replies
    1. We had some hard time graphing it. So, we thought this is the best way to make it clear and organized, but still you could be right about using one graph.
      Thank you.

      Delete
  8. Your table seems to be empty for number 1 and your graphs don’t appear to be the right shape. There are also two of them. There is a lot of white space in your table for number 2. Maybe you could reduce that and make the text bigger. You included two copies, plus a photo, for the graph in number 2. The shape is also strange. I think this could use some work. We got the resistance on our photoresistor to 14k, but 12k is pretty high. I wonder if there were different values. With a flash light we were able to get ours as low as 62 Ohms. Your Rube Goldberg circuit was a good idea. I think it would be easy to incorporate into a larger circuit.

    ReplyDelete
    Replies
    1. I just realize that there are couple of the same graphs. I don't know why it appears like this. We only published one. Thanks for noticing that. And as We replied to James Tompkins about question #4. We think it make sense to be different values for each group due to the different flash light we point to the photocell or due to the diffrent moderate light where we are sitting.
      Thanks.

      Delete