Blogsheet week 7
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)
Load
|
Pinch with finger (lightly)
|
Pinch with finger (hard)
|
Nothing
|
Resistance
|
19 kΩ
|
0.15 kΩ
|
0L
|
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).
NOTE: For the duration of this week's experiment, we used 360Ω resistors
Video 1: Lighting up different segments on display
b.
Using resistors for each segment, make the
display show 0 and 5. (EXPLAIN with PHOTOs)
The light on the 7 segment display depends on where the resistors are connected. Each pin on the segment display represents a line, forming any number from 0 to 9. For example, when we set our first resistor in pin 3, the first light to show up on the display was on segment "a" (the top line).
 |
| Image 1: Segment displaying 5 |
 |
| Image 2: Segment displaying 0 |
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:
You can't directly measure the output voltage because the 7 segment display is a ground seeking circuit. The driver doesn't send voltage to the display; it provides multiple paths to ground.
Truth Table 1: Corresponding inputs and outputs. Highlighted presents the displays we will show in the video below
Inputs
|
BCD Outputs
|
Display
|
|||||||||
A
|
B
|
C
|
D
|
a
|
b
|
c
|
d
|
e
|
f
|
g
|
|
0
|
0
|
0
|
0
|
1
|
1
|
1
|
1
|
1
|
1
|
0
|
0
|
0
|
0
|
0
|
1
|
0
|
1
|
1
|
0
|
0
|
0
|
0
|
1
|
0
|
0
|
1
|
0
|
1
|
1
|
0
|
1
|
1
|
0
|
1
|
2
|
0
|
0
|
1
|
1
|
1
|
1
|
1
|
1
|
0
|
0
|
1
|
3
|
0
|
1
|
0
|
0
|
0
|
1
|
1
|
0
|
0
|
1
|
1
|
4
|
0
|
1
|
0
|
1
|
1
|
0
|
1
|
1
|
0
|
1
|
1
|
5
|
0
|
1
|
1
|
0
|
1
|
0
|
1
|
1
|
1
|
1
|
1
|
6
|
0
|
1
|
1
|
1
|
1
|
1
|
1
|
0
|
0
|
0
|
0
|
7
|
1
|
0
|
0
|
0
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
8
|
1
|
0
|
0
|
1
|
1
|
1
|
1
|
1
|
0
|
1
|
1
|
9
|
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: Showing outputs 8 and 1 on circuit
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)
Image 3: Breadboard set up
Image 4: Oscilloscope reading
Note: We tried adjusting our reading, however it wouldn't change
Note: We tried adjusting our reading, however it wouldn't change
b.
Does your frequency and duty cycle match with
the theoretical value? Explain your work.
- According to the oscilloscope, our output voltage at pin 3 is 2 V.
- The measured duty cycle was 0.50 s while our theoretical value was 0.52 s
- The measured frequency was about 2 kHz while our theoretical value was 1.9 kHz
According to our findings, the frequency and duty cycle values do match with 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)
Video 3: Force sensing resistor 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.
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)
Truth Table 2
QD
|
QC
|
QB
|
QA
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
0
|
0
|
1
|
0
|
0
|
0
|
1
|
1
|
0
|
1
|
0
|
0
|
0
|
1
|
0
|
1
|
0
|
1
|
1
|
0
|
0
|
1
|
1
|
1
|
1
|
0
|
0
|
0
|
1
|
0
|
0
|
1
|
1
|
0
|
1
|
0
|
1
|
0
|
1
|
1
|
1
|
1
|
0
|
0
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
Video 4: Explanation of truth table
Video 5: Short video of output of QC
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 6: Different input combinations with XOR gate
b.
Connect XOR’s inputs to the BCD counters C and D
outputs. Explain your observation. (EXPLAIN with VIDEO)
Video 7: 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)\
Video 8: Signals of the 555 timer
(Sorry that it's sideways; it wouldn't flip orientation)
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)
Image 5: Our entire circuit
Video 9: Simplified circuit schematic of our circuit
8.
Using other logic gates provided (AND and OR),
come up with a different LED lighting scheme. (EXPLAIN with VIDEO)
Video 10: Using the OR gate
