Monday, February 20, 2017

WEEK 7

1. Force sensing resistor gives a resistance value with respect to the force that is applied on it. Try different loads (Pinching, squeezing with objects, etc.) and write down the resistance values. (EXPLAIN with TABLE)

Note: The harder you push down on the force sensing resistor, the less the resistance will be.

Force
Resistance (k)
No Force
0
Light Touch
20.97
Medium Touch
8.72
Hard Touch
0.76
Pinch
0.26
the force sensing resistor gives only a measurement of 0L, or overload, when there is no force applied to it. As we apply more force to the sensor, the resistance value goes down. This means if we apply a set voltage to the sensor, more current will be able to flow through it as we apply a greater force.

2. 7 Segment display:

a. Check the manual of 7 segment display. Pdf document’s page 5 (or in the document page 4) circuit B is the one we have. Connect pin 3 or pin 14 to 5 V. Connect a 330 Ω resistor to pin 1. Other end of the resistor goes to ground. Which line lit up? Using package dimensions and function for B (page 4 in pdf), explain the operation of the 7 segment display by lighting up different segments. (EXPLAIN with VIDEO).


Applying voltage to specific pins on the seven segment display, we can get different segments to light up. This will enable us to display numbers 0-9 later in the lab. 

b. Using resistors for each segment, make the display show 0 and 5. (EXPLAIN with PHOTOs)


























Depending on where the resistors are located will determine what number is shown on the counter. 



3. Display driver
 (7447). This integrated circuit (IC) is designed to drive 7 segment display through resistors. Check the data sheet. A, B, C, and D are binary inputs. Pins 9 through 15 are outputs that go to the display. Pin 8 is ground and pin 16 is 5 V.

a. By connecting inputs either 0 V or 5 V, check the output voltages of the driver. Explain how the inputs and outputs are related. Provide two different input combinations. (EXPLAIN with PHOTOs and TRUTH TABLE)
Number
A
B
C
D
0
0
0
0
0
8
1
0
0
0

The four inputs create a 4-bit binary number--with D as the most significant digit and A as the least significant digit--that corresponds to the number displayed. Each combination of inputs, with "0" representing 0 V applied to that pin and "1" representing 5 V applied to the pin, generates a combination of seven outputs, activating up to seven of the pins 9-15 on the display driver. Each of these output pins corresponds to one of the pins.on the Seven Segment Display and will allow us to display the number 0-9 when connected correctly



pictures above is by using #0






pictures above by using #8



b. Connect the display driver to the 7 segment display. 330 Ω resistors need to be used between the display driver outputs and the display (a total of 7 resistors). Verify your question 3a outputs with those input combinations. (EXPLAIN with VIDEO)



We are able to change the output number based on where the resistors are connected.  You see here that connecting a single resistor to a different output changes the number from 0 to 8.  

4. 555 Timer:
 a. Construct the circuit in Fig. 14 of the 555 timer data sheet. VCC = 5V. No RL (no connection to pin 3). RA = 150 kΩ, RB = 300 kΩ, and C = 1 µF (smaller sized capacitor). 0.01 µF capacitor is somewhat larger in size. Observe your output voltage at pin 3 by oscilloscope. (Breadboard and Oscilloscope PHOTOs)






b. Does your frequency and duty cycle match with the theoretical value? Explain your work.

A duty cycle is the percentage of the period when this 555 timer's signal is active. From our oscilloscope measurement, it seems as if our timer's signal is active closer to 60% of the time, when there is a reading of 5V and inactive closer to our calculated value of 40%, when the oscilloscope measured 0V. However, if you look at the next question, you can see that when our timer's signal is inactive, that is, we have not put any pressure on the force sensor, then the oscilloscope reads 5V and only begins to cycle between 0 and 5 V once we put pressure on the force sensor.



c. Connect the force sensing resistor in series with RA. How can you make the circuit give an output? Can the frequency of the output be modified with the force sensing resistor? (Explain with VIDEO)

With the force sensing resistor attached to the 555 timer's circuit, we need to apply pressure to the sensor in order to see an output. We found that the frequency increased very slightly when we applied a lot of force compared to only a small amount of force.

5. Binary coded decimal (BCD) counter (74192). This circuit generates a 4-bit counter. With every clock change, output increases; 0000, 0001, 0010, …, 0111, 1000, 1001. But after 1001 (which is decimal 9), it goes back to 0000. That way, in decimal, it counts from 0 to 9. Outputs of 74192 are labelled as QA (Least significant bit), QB, QC, and QD (Most significant bit) in the data sheet (decimal counter, 74192). Use the following connections: 5 V: pins 4, 11, 16. 0 V (ground): pins 8, 14. 10 µF capacitor between 5 V and ground.
a. Connect your 555 timer output to pin 5 of 74192. Observe the input and each output on the oscilloscope. (EXPLAIN with VIDEO and TRUTH TABLE)

Clock input
Qa
Qb
Qc
Qd
Dicimal output
0
0
0
0
0
0
1
0
0
0
1
1
2
0
0
1
0
2
3
0
0
1
1
3
4
0
1
0
0
4
5
0
1
0
1
5
6
0
1
1
0
6
7
0
1
1
1
7
8
1
0
0
0
8
9
1
0
0
1
9









13 comments:

  1. We got similar values for the pressure resistor. I noticed other groups got really low values. I was personally surprised by the amount of resistance that those resistors could supply. Also I seems weird to me that when no pressure is applied there is 0 ohms and it does not allow current to flow. However, when you supply maximum pressure it also brings the resistor to nearly 0.

    ReplyDelete
    Replies
    1. yes you are right the FSR give a low resistance value when you make a high force in it
      thanks for your comment

      Delete
  2. Obviously you guys have some stuff to add still but what you have right now looks good. We got different values for the pressure sensor, our resistance values were a lot higher. Do you think this is because they're different units all together or something else? Like Alec said, I also found it odd how when there was no pressure there was 0 resistance, I thought it would be the most resistance. Also I'm curious to see what you guys put for 5 b. for that question it took us quite some time to figure out what these words meant but we eventually found out how to calculate them using equations given in the manual. Nice job this week.

    ReplyDelete
    Replies
    1. the FSR values depends in the high force you gave to it so because of that we got different values
      thanks for your comment

      Delete
  3. Good job so far, definitely need to finish the rest up but for the most part it looks really good. Your values for your pressure sensor was far off from ours. I found it very interesting as to how those worked, it was cool to see the different values obtained from the pressure. Finish up the rest and you'll have a great blog!

    ReplyDelete
    Replies
    1. the FSR values depends in the high force you gave to it so because of that we got different values
      thanks for your comment

      Delete
  4. From the questions I think your work is good and we have similar results to you, but you need to add more explainaton and add truth tables. Also you have to finish the rest of the blog.
    Good job

    ReplyDelete
    Replies
    1. thanks for your comment
      we add more explanation and the truth table for most of them

      Delete
  5. We also got a reading of zero ohms for no force on the force sensing resistor but im starting to think that intuitively based on the rest of the data that the value for no force must be infinite. However, possibly because there is still a conection somehow is why there is no overload reading. I am not sure, any thoughts on this?

    ReplyDelete
    Replies
    1. the FSR values depends in the high force you gave to it so because of that we got different values
      thanks for your comment

      Delete
  6. It is interesting to me that the less force you put on the force sensing resistor, the more resistance it has. This is counter-intuitive to what I would expect. It would be cool to learn why this is I think.

    ReplyDelete
    Replies
    1. the FSR values depends in the high force you gave to it so because of that we got different values
      thanks for your comment

      Delete