Monday, February 20, 2017

Blog Report 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)

Table 1: Data for Force Sensing Resistor with
range of pressures

  • The pressure pad decreases the amount of resistance, the more pressure applied the more current it allows to flow.

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).

Video 1: Demonstrates how a 7 segment display works

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

Photo 1: Number zero displayed by
pins 1, 2, 7, 8, 10 and 13 to ground 
through 330Ω resistors.
Photo 2: Number five displayed by 
pins 1, 2, 8, 10 and 11 to ground 
through 330Ω resistors.

  • The LED output depends on which cathodes are connected to the ground.

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)
UPDATE! You cannot actually measure the output voltages directly (I challenge you to figure out why!). You need to connect an LED and a resistor. LED’s positive terminal will go to 5 V. Negative terminal will be connected to your outputs via a resistor. The circuit would look like below:

Photo 3: Shows the voltage reading across the
LED when it is on.
Photo 4: Shows the voltage reading across the
LED when it is turned off.

Table 2: Is a truth table based off the inputs
for the 7447 Display Driver (IC).

  • The reason you cannot measure the voltages directly is because you're not completing the circuit, you need to ground the end of the connection.

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)

Video 2: Testing to make sure that our truth table is accurate. We placed inputs A, B, C, and D all in alphabetical order to make it easier for us to control the inputs. The binary input that is entered through highs and lows will be translated to a whole number on the 7 segment display. This is just proven in the video. 

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)

Photo 5: Shows a picture of our circuit laid
out on the breadboard.
Photo 6: Shows the oscilloscope reading
of the 555 timer's output

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

  • According to the theoretical duty cycle, since our clock's rate is continuously changing between high and low, the cycle is about 40%. In the 555 timer's pdf manual there are equations for the Duty Cycle and frequency they can be calculated using the following: 
Equations for Frequency and Duty Cycle for Astable Operation circuit of
a 555 timer, it's theoretical values can be calculated using these.

t1 = 0.3149685 s
t2 = 0.209979 s
T = (t1 + t2) = 0.5249475 s

f = (1 / T) = 1.9049524 Hz
D = (0.40) = 40%

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)

Video 3: Putting pressure on the force sensor is how you make the circuit give an output. The frequency of the output can be modified by adjusting the force on the force sensor. This is shown in the video. 

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)

Video 4: This video shows the input from the timer alongside the output from QB. This is just to show the comparison between the two signals. Each signal from the 74192 is a little different because they contain different highs and lows. 

Table 3: Truth table shows 74192 output from the 555 timer.

6. 7486 (XOR gate). Pin diagram of the circuit is given in the logic gates pin diagram pdf file. Ground pin is 7. Pin 14 will be connected to 5 V. There are 4 XOR gates. Pins are numbered. Connect a 330 Ω resistor at the output of one of the XOR gates.

a.) Put an LED in series to the resistor. Negative end of the LED (shorter wire) should be connected to the ground. By choosing different input combinations (DC 0V and DC 5 V), prove XOR operation through LED. (EXPLAIN with VIDEO)

Video 5: Here is a video testing different combinations on the XOR gate and proving its truth table. When the inputs are opposite, the light is on. When the inputs are the same, the light is off. 

b.) Connect XOR’s inputs to the BCD counters C and D outputs. Explain your observation. (EXPLAIN with VIDEO)

Video 6: This video shows the C and D outputs from the 74192 plugged into the XOR gate. When the signals are the same, the light goes off. When the signals are opposites, the light turns on. 

c.) For (6b.), draw the following signals together: 555 timer (clock), A, B, C, and D outputs of 74192, and the XOR output. (EXPLAIN with VIDEO)

Video 7: Explains how  A, B, C, D, Clock, and Xor are Related

Photo 7: Picture of signals explained in video above.

7. Connect the entire circuit: Force sensing resistor triggers the 555 timer. 555 timer’s output is used as clock for the counter. Counter is then connected to the driver (Counter’s A, B, C, D to driver’s A, B, C, D). Driver is connected to the display through resistors. XOR gate is connected to the counter’s C and D inputs as well and an LED with a resistor is connected to the XOR output. Draw the circuit schematic. (VIDEO and PHOTO)

Video 8: This is a video of the entire circuit connected and running. We are unsure why only even numbers are counting. We tried and tried, but could not find a solution. Sometimes it was just odd numbers as well. 

Photo 7: A schematic of our XOR Gate LED
and 7 segment display 

8. Using other logic gates provided (AND and OR), come up with a different LED lighting scheme. (EXPLAIN with VIDEO)

Video 9: This is a video showing Justin's alternate setup using the AND and OR gates that were provided to us. The AND gate's output is connected to the input of an OR gate. The video explains the different combinations that make the light work.