Week 7, 2/22/2016 - 2/26/2016

Digital Circuits

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)

The more force applied to the force sensing resistor, the lower resistance value it will have. Table 1 below shows the relationship between the load and the resistance.

Load	Resistance Ω
No Load	Open loop, ideally infinite resistance
Pinching	2,000
Phone on top of sensor	1,300
Squeezing	840

Table 1: This table displays the relationship between load and resistance for the force sensor.

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).

The very top line lit up when you connected the resistor to pin 1. Depending on where you place the resistor, different lines will light up. Video 1 below explains this in detail. From the blog we can know which pin will light which segments.

Video 1: This video explains how to light up different segments on this display.

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

Using resistors we were able to construct numbers 0-5. Pictures 1-6 below show our results. Applying power to pin 1,2,7,8,10,13 we can display number 0 on the 7-segment display. Same if we applying power to 1,2,8,10,11, display will show number 5.

Picture 1: This picture has 0 as the display.

Picture 2: This picture has 1 as the display.

Picture 3: This picture has 2 as the display.

Picture 4: This picture has 3 as the display.

Picture 5: This picture has 4 as the display.

Picture 6: This picture has 5 as the display.

BONUS VIDEO:

For the display sensor diagram we noticed that there was "dp" next to pin 9. We wondered what pin 9 would do and decided to investigate. We found out that pin 9 lit up the dot next to the numbers on the display. Picture 7 below shows the diagram for the display sensor and video 2 explains what we found.

Picture 7: This picture is the display sensor diagram. Notice the "dp" by pin 9.

Video 2: This video explains the function of pin 9 on the display

3. Display driver (7447). This integrated circuit (IC) is designed to drive 7 segment displays 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)

7447 can transfer 4 bits binary number into 7 segments output which can use to drive 7-segments display. We were not able to measure the voltage of the driver. Instead we showed voltage by showing two different outputs on the display. You cannot read a voltage from the driver because it is ground seeking, it never sends voltage to the display, it provides paths to the ground. Pictures 8 and 9 are an output to an LED to show that changing the inputs can change your results. Chart 1 is the truth table for the driver.

Picture 8: By changing the inputs we were able to light an LED.

Picture 9: By changing the inputs we were able to turn off the LED.

Chart 1: This chart is the truth table for inputs and outputs of the Driver

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) 

Depending on the inputs and outputs you will have different results. Video 3 below shows us changing the inputs in real time and you can see how the display changes.

Video 3: This video shows us changing the inputs, and therefore the outputs

4. 555 Timer:

a.     Construct the circuit in Fig. 14 of the 555 timer data sheet. V

CC= 5V. No RL (no connection to pin 3). RA = 150 kΩ, R = 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)

Below are pictures 10 and 11 that show our breadboard and our oscilloscope readings.

Picture 10: This is a picture of our breadboard with the timer

Picture 11: This is our oscilloscope readings with the timer.

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

Our calculated frequency is a bit higher than the measured. To calculate the frequency we divided 1.44 by our resistance times our capacitor. This came out to be 1.44/(750 ohms * 1 micro farrad) which equaled to be 1920. Our measured value was 1623.54. Our duty cycle was measured to be higher than the theoretical value. Our calculated value was found by diving Rb by Ra+2Rb. Which gave us D = Rb/(Ra+2Rb). That equaled out to be .4. By counting the squares our actual measured value was closer to .56.

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) 

By applying pressure to the resistor you can make the circuit give an output. From what we were able to tell you cannot change the frequency of the output with the force sensing resistor very much. The video, video 4, describes this below.

Video 4: This video shows us using the force sensing resistor to get an output

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.  0V (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)

The binary clock sends a pulse that is ready by the driver as binary. The binary counts up and depending on the different binary you will get different outputs. The display then counts upward from 0-9 depending on what the binary reads. Video 5 below explains this and chart 2 shows the truth table.

Video 5: This video is showing the inputs and outputs of the timer to the 74192

Chart 2: This chart is the truth table for the 74192

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 Ωresistor 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)

When we connected the LED to the XOR gate we found that it worked according to an XOR truth table. When only one of the inputs A or B read at 1 the LED turned on. When both read at 1 or 0 the LED did not work. Video 6 shows this and Chart 3 is the XOR truth table.

Video 6: This video shows an LED with a XOR gate.

Chart 3: This chart is a XOR gate's truth table.

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

If you refer to charts 2 and 3 you can see that whenever inputs C or D have a 1 that the LED will light up. However, whenever neither or both have a 1, the LED will not light up. Video 7 below explains this.

Video 7: This video shows the XOR's inputs into the BCD counters outputs.

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)

We drew the signals in the video below. The clock goes off of set pulses and then the values of A, B, C, and D will change based upon that. Please refer to Chart 2 to see how it changes. Every time there is a pulse, the binary value increases by 1 and then after 9 is reset back to 0. The XOR is connected to CD and will read 0 for any value from 0-3 and 1 from any value 4-9. Video 8 below shows our drawing and helps explain this concept.

Video 8: This video shows our drawings of the signals and helps explain the concepts.

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)

We connected all of the circuit components and were able to make a circuit that counts when you apply pressure to the force sensing resistor. Video 9 shows our circuit in action. Picture 12 is a picture of our breadboard and picture 13 is a drawing of our circuit schematic.

Video 9: This video is our circuit in real time

Picture 12: This is a photo of our completed circuit

Picture 13: This is our circuit schematic

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

We changed the inputs to A and B and then switched gates to an AND gate. Referring to hart 2, when the inputs are 3 and 7, both A and B will read at 1. That means that the LED will light up. Video 10 shows our circuit in real time and chart 4 is an AND gate truth table.

Video 10: This video shows our circuit with an AND gate working in real time

Chart 4: This chart is the truth table for an AND gate