Lab 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)

What was placed on the sensor	Multimeter reading (K Ω)
A phone	300
Pinched	6
A computer mouse	85
Alligator clip (attached)	22.3

Table: The readings given off by the force sensor when objects placed on it

The force sensor when it has no pressure on it gives a reading of over loaded when connected with the digital multimeter. However once some pressure was added to it, the multimeter gave off a reading.

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: 7 Segment Display with Varied Lit Segments

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

Image: 0 Shown on 7 Segment Display

Image: 5 Shown on 7 Segment Display

Each input of the 7 Segment display powers one of the segments of the display, so connecting a resistor at the necessary inputs to the ground will complete the circuit in such a way that will light the desired segments. 

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)

Image 1: Display Driver Inputs A'B'CD' with Output d

Image 2: Display Driver Inputs A'B'CD' with Output f

Image 3: Display Driver Inputs A'B'C'D' with Output c

Image 4: Display Driver Inputs A'B'C'D' with Output g

Table: Truth Table from 7447 Display Driver Manual

For the circuit labels above an apostrophe indicates that the terminal is grounded, and thus considered a low input. Contrarily the terminals labeled without an apostrophe are considered to be on, or a "high" output. So, looking at the truth table, for all inputs at a low except input C set to high, the output terminal d should be off and the output terminal f should be on. Additionally, with all input terminals set to low, output g should be on and c should be off.

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:
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: Display Driver and 7 Segment Display

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)

Picture: Wave generated by the 555

Picture: 555 set up on breadboard

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

The measured values that we found for the frequency was about 2.4 Hz which has about a 20% error from the calculated which could be from a bad wire or misreading the oscilloscope measurement. The measured duty cycle we found was a .31 which is also off from the theoretical value.

Picture: Work for calculating the theoretical values

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)

 You can make the circuit give off an input by adding pressure to the force sensor to lessen the resistance in the force sensor the frequency can be altered by adding more or less pressure to the sensor. 

Video 3: Force Sensor Affecting the Frequency of 555 Timer

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: Timer Inputs and Outputs of 74192

Counter	QD	QC	QB	QA
0	0	0	0	0
1	0	0	0	1
2	0	0	1	0
3	0	0	1	1
4	0	1	0	0
5	0	1	0	1
6	0	1	1	0
7	0	1	1	1
8	1	0	0	0
9	1	0	0	1

Table: Counter Truth Table

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: LED as the Output of an XOR Gate

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

Video 6: LED at C and D Outputs of BCD Counter

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: The different waves depending on A-D, and XOR output

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 7: Circuit with 555 Timer, XOR Gate, Display Driver, 7 

Segment Display, LED, and Force Sensor

Picture: Circuit with all components combined

Picture: Schematic of the combined circuit

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

Video 8: Final Circuit with a Changed Lighting Scheme