Lab 9

Blogsheet week 9

1.  Measure the resistance of the speaker. 

       It keeps fluctuating between 7.9 and 8.2.

2. Build the following circuit using a function generator setting the amplitude to 5V (0V offset). What happens when you change the frequency? (video)

Fig 1. Test setup for the speaker.

Fill out the following table.

Frequency (kHz)	Observation
1	Steady squeal
2	Lower pitched tone
3	Higher pitched whine
4	Even more annoying
5	Most annoying

3.  Add one resistor to the circuit in series with the speaker (first 47 Ω, then 820 Ω). Measure the voltage across the speaker. Briefly explain your observations.

Voltage with the 47 Ohm resistor:  375 mV(rms) (1 kHz)

Voltage with the 820 Ohm resistor:  54 mV(rms) (1 kHz)

We noticed immediately that the pitch of the tone is lower as we make the resistor bigger.  The volume also decreases the higher the resistance.

Fill the following table.

Resistor Value (Ω)	Oscilliscope Output (Vrms)	Observation
47	0.396	Low pitched hum
820	0.054	A quiet low pitched hum

4.     Build the following circuit. Add a resistor in series to the speaker to have an equivalent resistance of 100 Ω. Note that this circuit is a high pass filter. Set the amplitude of the input signal to 8 V. Change the frequency from low to high to observe the speaker sound. You should not hear anything at the beginning and start hearing the sound after a certain frequency. Use 22 nF for the capacitor.

Fig. 2 Test setup for high pass filter

a.       Explain the operation.  (video)

b.      Fill out the following table by adding enough (10-15 data points) frequency measurements. Vout is measured with the DMM, thus it will be rms value.

Frequency (Hz)	Vout (Vrms)	Vout(rms) / Vin(rms)
1000	0.0854	0.0106
42000	2.64	0.33
56000	3.04	0.38
83000	3.46	0.433
100000	3.58	0.448
160000	3.87	0.484
233000	4.05	0.506
308000	4.13	0.516
377000	4.22	0.528
410000	4.27	0.534
500000	4.46	0.558
801000	5.77	0.721
901000	6.6	0.825

c.       Draw Vout/Vin with respect to frequency using Excel.

Vout/Vin with frequency as the x-axis and the vout/vin as the y-axis

d.      What is the cut off frequency by looking at the plot in b?
          901 kHz

5.     Design the circuit in 4 to act as a low pass filter and show its operation. Where would you put the speaker? Repeat 4a-g using the new designed circuit (e, f, and g are for blogI).

        For the low pass filter you would connect the speaker across the capacitor much like you connect the oscilloscope. 

a.  Explain the operation (video)

b.  Fill out the following table by adding enough (10-15 data points) frequency measurements.  Vout is measured with the DMM, thus it will be the rms value.

Frequency (Hz)	Vout (rms)	Vout (rms) / Vin (rms)
679	5.9	0.738
1000	5.99	0.749
6000	5.8	0.725
15000	5.6	0.7
23000	5.3	0.663
46000	4.3	0.538
52000	4.09	0.511
57000	3.89	0.486
66000	3.57	0.446
77000	3.22	0.403
85000	2.98	0.373
92000	2.8	0.35
121000	2.26	0.283
151000	1.86	0.233

c.  Draw Vout/Vin with respect to frequency using excel.

Vout/Vin charted with frequency as the x axis and vout/vin as the y axis

d.  What is the cut off frequency by looking at the plot in b?

5.6 kHz

6.       Construct the following circuit and test the speaker with headsets. Connect the amplifier output directly to the headphone jack (without the potentiometer). Load is the headphone jack in the schematic. “Speculate” the operation of the circuit with a video.

Lab 8

Blogsheet week 8

Rube Goldberg Take 2

Draw and explain a Rube Goldberg design that will include the following components:

·       Digital

·       Motor

·       Relay

·       Opamp

·       Temperature sensor

·       LED

The setup should be considered to last 30 seconds.

Make sure to include enough photos, videos, and explanations for each “transition” or step. Explain your circuits. Put at least 2 issues/problems/struggles you faced during the project.

          For our Rube Goldberg design we decided make a design that would pull a paper flag up a flagpole and, when the timing was right, break the circuit so the motor pulling both strings would stop.

         We kept the same design and setup for the week 7 lab which we didn't disassemble after we finished and added on an OpAmp, Temp sensor, relay, and a larger motor.  The reason we used another motor wasn't because we didn't have enough power to pull the flag or to pull the wire out of the bread board, but because it had 2 axels which could be more easily utilized to pull two things at once.

The drawing of our complete circuit, including values for resistors and voltage sources

               Once we decided what we wanted to do we pulled out our week 7 design and added the OpAmp, relay, temp sensor, transistor, and motor. 

Our set up near the beginning of the project.

         We decided that we wanted the design to be completely automatic once we had set it in motion, so we decided that we would use a domino like effect to land something on the pressure sensor to start the clock and begin the process of pulling up the flag.  Since we wanted it to be fully automatic we didn't use a heat source (though we decided we might have to if we wanted to speed it up in any way or if we needed to get more voltage to the motor) so we configured the OpAmp to produce enough voltage after the temp sensor to run the motor.  Once of our biggest struggles was figuring out which resistors to use with the OpAmp to produce the desired power and speed so we could reach the 30 second minimum. 

The next iteration of our machine before we decided on another arrangement. 

        For our XOR gate we used a constant input of 1 from the 5V source and then we used the A output from the display driver (alternating between 0 and 1 every second)  to give us the right timing.  The LED would turn on while the motor was running and would turn off when it wasn't.  This was another area where we had an issue, we found that any of the inputs (B, C, or D) from the display drivers that let the motor run for more than a second at a time was too fast for the 30 second threshold. 

        The video above shows our rearranged machine using C as the output of the display driver, it moves much too fast for the 30 second threshold so we needed to rethink the output that we were going to use. 

       Another challenge for our machine was that the motor had just enough power to turn at the speed we wanted, so any additional force on the string would cause the motor not to turn.  In the video below the motor doesn't turn, and the reason for that is that the "guide" for the string, so that it wouldn't fall off track and not wind around the motor, was catching.

      After this we changed the guides so that they wouldn't hamper the progress of the string so we could get the timing down without additional difficulties.  In the end we got it nearly to what we wanted, the video below is when we demonstrated it for the class.

A picture of our completed operation

Engineering Rules!

Lab 7

Blogsheet 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)

Fig 1.

Resistance (Ω)	Object
4.6k	Coffee mug on edge
12.2k	Keys
2k	Index finger resting
208.6	Index finger pressing
78.3	Thumb pressing

      
We use various objects and pressures of fingers against the sensor.  As you can see the more pressure that is placed against the sensor the less resistance we get.

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).

A video showing us connecting inputs to different segments of the 7 segment display.

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

A picture showing the 7 segment display with 0 displayed.

A picture showing the 7 segment display with 5 displayed.

When using the 7 segment display, you can display whichever number you want between 0 and 9 by manipulating the pins that the resistors connect to.  To light up a segment you connect the resistor to that segments pin and then to 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)
For example if we wanted to display the numbers 0, 4, or 5 these would be the inputs for the display driver:

Desired inputs for 0, 4, or 5.

This is the truth table that relates the inputs of the 7447 to the outputs which would be connected to the 7 segment display

Truth table for the Display Driver

The output to the LED in this picture is 0.

The output to the LED in this picture is 1.

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)

A video showing us getting different results with different inputs.

4.       555 Timer:

a.       Construct the circuit in Fig. 14 of the 555 timer data sheet. V_CC = 5V. No R_L (no connection to pin 3). R_A = 150 kΩ, R_B = 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)

A picture showing our breadboard setup of the 555 timer.

A picture showing the output of pin 3 by the 555 timer.

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

Our theoretical is frequency is 1.92 Hz and the theoretical duty cycle is 0.4.  As you can find from our oscilloscope picture in the previous part, the frequency we measured is 1.62 Hz and the duty cycle was around 0.4.

Duty Cycle calculation

Frequency calculation

c.       Connect the force sensing resistor in series with R_A. 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)

A video showing our force sensing resistor giving an output while connected to the 555 time.  Varying pressures give different frequencies.

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 Q_A (Least significant bit), Q_B, Q_C, and Q_D (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)

A video showing the output of the counter on the oscilloscope.

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)

A video showing the operation of the XOR gate.

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

A video showing the output of the C and D outputs connected to the XOR gate.

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)

The 555 timer, A, B, C, and D outputs of 74192, and the XOR output signals drawn together.

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)

A picture of our entire circuit.

A drawing of our circuit schematic.

A video showing the operation of our entire circuit

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

A video showing the operation of our entire circuit with an added output.