Week Seven

Week 7

Not Shocking People

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.

Figure 1: Resistance values with different forms of applied pressures.

From our data, when there is no applied force, it is read as if there is no connected circuit or resistor at all with the reading of 0L, when a little force was applied a resistor measurement could be read. However, as we increased the amount of force on the FSR, the resistance decreased. 

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).

Figure 2: Video explaining the 7 segment display circuit and its operations, with demonstration.

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

Figure 3: Placing the resistors in series with the negative ends of the correct diodes that light the display, the number 0 is able to be represented in the display.

Figure 4: Representation of 5 with the display.

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)

Figure 5: Showing when the d output pin in the display driver gave a 1 output (5V), and the light off due to such.

Figure 6: When d output pin gives a 0 output(0V), and the light turns on.

Figure 7: When the binary representations of decimal numbers are represented in the driver inputs of A,B,C, and D, the outputs of a,b,c,d,e,f, and g will change.

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)

Figure 8: Video Explaining the relationships between the inputs and outputs of the driver with demonstration.

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)

Figure 9: Overhead shot of circuit setup

Figure 10: Close-up shot of Timer circuit setup

Figure 11: Observed oscilloscope readings

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

Theoretical Value:

Frequency = 1.44/[(150k + 2 * 300k)*.000001] =  1.92 Hz;  

Duty Cycle = 300k/(150k+2*300k) = 0.4

Measured Value: 

Frequency = 0.5 Hz

Duty Cycle = 0.4

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)

Figure 12: Video explanation of Pressure Resistor

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)

Figure 13: Observed output of the 74192 when connected to the timer

Figure 14: Truth table for example

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)

Figure 15: Proof for XOR operation with LED and Circuit

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

Figure 16: Observations of LED connected to BCD's C and D 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)

Figure 17: Explanation of BCD + Timer outputs and relations

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)

Figure 18: Full circuit and explanation of its operations

Figure 19: Full circuit diagram

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

Figure 20: Fun with logic gates (Alternate Operations/LED sequence)