Monday, January 23, 2017

Week 3: Equivalent Resistance and Potentiometer

Question 1: Compare the calculated and measured equivalent resistance values between the nodes A and B for three circuit configurations given below. Choose your own resistors.
figure 1, circuits for question 1
Circuit Calculated Resistance Meausred Resistance
A 77.31 Ohms 78.2 Ohms
B 378.33 Ohms 377 Ohms
C 385.91 Ohms 385 Ohms

Question 2:  Apply 5V on a 120 Ω resistor. Measure the current by putting the multimeter in series and parallel. Why are they different?

In series, the DMM showed a current of about 40 mA, while in parallel, it showed 0 mA. This is due to the fact that when the current is measured in series, the current flows normally over the resistor and through the DMM. However in parallel, the resistor is shorted, making a resistance of nearly 0 Ohms. Due to Ohm's Law, I = V/R, this results in nearly infinite current. The DMM handles this by outputting 0 and giving an error notification.

Question 3:  Apply 5 V to two resistors (47 Ω and 120 Ω) that are in series. Compare the measured and calculated values of voltage and current values on each resistor.
Measured:
Voltage across 47: 1.4 volts
Voltage across 120: 3.6 Volts
Current: 30 mA
Calculated:
Voltage across 47: 1.4 Volts
Voltage across 120: 3.59 Volts
Current: 29.9 mA

Question 4:  Apply 5 V to two resistors (47 Ω and 120 Ω) that are in parallel. Compare the measured and calculated values of voltage and current values on each resistor.
Measured:
Current across 47: .1 Amps
Current across 120: .03 Amps
Voltage 5 volts
Calculated:
Current across 47: .1068 Amps
Current across 120: .0418 Amps
Voltage 5 volts

Question 5:  Compare the calculated and measured values of the following current and voltage for the circuit below: (breadboard photo) a. Current on 2 kΩ resistor, b. Voltage across both 1.2 kΩ resistors.
figure 2, breadboard photo for question 5


figure 3, circuit for question 5

a.) we measured 2.06 mA on the 2k Ohms resistor.
b.) 1.) .863 Volts was measured across the first 1.2k Ohms resistor in the circuit from the power source
b.) 2.) -.732 Volts was measured across the second 1.2k Ohms resistor in the circuit from the power source

Question 6:  What would be the equivalent resistance value of the circuit above (between the power supply nodes)?
For the circuit above (figure 3) the calculated resistance we figured out was 2265.74 Ohms.


Question 7:  Measure the equivalent resistance with and without the 5 V power supply. Are they different? Why?
Measuring the resistance without the power supply we got 2.464 kOhms. When we measured with the power supply we measured 0.563 kOhms. They were different because when you measure resistance with he power supply in line with the circuit also at the same points then the multi-meter with measure the power supply's resistance in parallel with the circuit.

Question 8:  Explain the operation of a potentiometer by measuring the resistance values between the terminals (there are 3 terminals, so there would be 3 combinations).(video)

figure 4, operation of a potentiometer


Question 9:  What would be the minimum and maximum voltage that can be obtained at V1 by changing the knob position of the 5 KΩ pot? Explain.
figure 5, circuit for question 9
The maximum voltage at V1 that could be obtained would be 5 volts. That would be when the knob is set at its max position. This is because the wiper pin would be at the same level as the negative bottom pin giving the whole potentiometer 5k resistance, leaving only that one 5k Voltage drop. The minimum voltage at V1 would be 0 volts when the knob is turned to its minimum position. This is because the wiper pin would have a resistance of 0 with the pin the that power supply is connected to leaving no voltage drop. If in the middle position there would be a voltage drop over 2.5k Ohms.

Question 10:  How are V1 and V2 (voltages are defined with respect to ground) related and how do they change with the position of the knob of the pot? (video)
figure 6, circuit for question 10


When measuring V it 1 won't change at all because it is measured right at the voltage source but V2 will change as it is measured above the potentiometer acting as a variable resistor.


figure 7, video measuring V1 and V2


Question 11:  For the circuit below, YOU SHOULD NOT turn down the potentiometer all the way down to reach 0 Ω. Why?
figure 8, circuit for question 11
Then the circuit would be shorted out though the potentiometer and no current would flow through the 1k Ohms resistor.


Question 12:  . For the circuit above, how are current values of 1 kΩ resistor and 5 KΩ pot related and how do they change with the position of the knob of the pot? (video).


figure 9, video showing potentiometer 



Question 13:  Explain what a voltage divider is and how it works based on your experiments.
A voltage decider works by putting two resistors in series and taking voltage from the middle of the resistors. Because across the whole circuit with one resistor, if you apply 5 volts then you'd get 5 volts from the top to ground. With two resistors apply 5 volts there is a different voltage drop at the top of each of them in series. Therefore at the top of the second resistor in series you get a value between 5 and 0 volts.

Question 14:  Explain what a current divider is and how it works based on your experiments.

A current divider is a way to control the input current source to a lower value. This is done with parallel resistors. In our experiment, we used a potentiometer for one of the resistors, allowing us to control the current using the knob.

Friday, January 20, 2017

Week 2: Power Supply and Digital Multimeter (DMM)

Question 1: What is the role of A/B switch? If you are on A, would B still give you a voltage?

The role of the A/B switch is to connect the built in analog Voltage and Current meters in the power supply to either Channel A or B. This allows for the user to monitor freely between both the A power supply and the B power supply without any components needing to be altered.

The power supply for A or B will not be stopped by the A/B switch, it is wholly for the switching of the analog meters.

Question 2: In each channel, there is a current specification (either 0.5 A or 4 A). What does that mean?

For the FIXED power supply (4 A), this is the current always going through it.
For the A and B power supplies (0.5 A), this is the max current output for each power supply, however these two can adjust the current output from 0A-0.5A


Question 3: Your power supply has two main operation modes for A and B channels; independent and tracking. How do those operation work?

In independent mode the power supply has A and B act completely separate from each other. When in a tracking mode A and B work together to either provide a higher voltage as in series tracking mode, 0-48 volts, or a higher amperage as in parallel tracking mode , 0-1 amp. In tracking mode you use B- and A+ as your terminals.

 
Fig. 1: Video explanation of operation modes.



Question 4: Can you generate +30 V using a combination of the power supply outputs? How?

To generate positive 30 volts we have the power supply in tracking parallel mode With both A and B at 15 volts. Using B- connected to ground and negative lead of the DMM, and A+ connected to the positive lead of the DMM.

Fig. 2: +30 Volts with the power supply in series tracking mode. Ground connect to negative.

Question 5: Can you generate -30 V using a combination of the power supply outputs? How?

To generate negative 30 volts we have the power supply in tracking parallel mode With both A and B at 15 volts. Using B- connected the positive lead of the DMM, and A+ connected ground and the negative lead of the DMM.
Fig. 3: +30 Volts with the power supply in series tracking mode. Ground connect to positive.

Question 6: Can you generate +10 V and -10 V at the same time using a combination of the power supply outputs? How?

To generate positive 10 volts and negative 10 volts at the same time we have the power supply independent mode With both A and B at 10 volts. B- connected to ground, B+ open allows for B to give positive 10 volts. to get A to give negative 10 Volts we have A+ grounded and connect to the negative lead of the DMM and A- to the positive lead of the DMM.
Fig. 4: +10 volts from B and -10 volts coming form A

Question 7: Apply 5V to a 100 Ω resistor and measure the current by using the DMM. Compare the reading with the current meter reading on the power supply. At what angle of the current knob makes the LED light on? If you keep on decreasing the current limit, what happens to the voltage and current?

33.36mA is what the DMM measured when the resistor was hooked up to 5 volts. The power supply also measure about the same with the lever arm about a third of the way to the 100 tick on the current meter. The Led on the power supply that signals if the current is being limited turns off about 15 to 20 degrees from the far left or no current flowing. As the current limit knob is turned counter clockwise depressing the max current allowed to flow, the current and voltage decrease.

Fig. 5: Digital Multimeter and current dial experiment.

Question 8: Where is the fuse for the power supply? What is it for?

The power supply's fuse is located on the back plate of the device, directly below the outlet plug on the device. It is there to protect the delicate components of the power supply. By having the current go through the fuse first, the fuse acts as a gate to the rest of the device. If the current gets too high, the fuse breaks the connection, stopping flow of current to the power supply. Generally, the fuse will only be tripped if there is a problem in the power grid, i.e. power surges.

Question 9: Where is the fuse for the DMM? What is it for?

The access point for the fuse is located on the front of the DMM, in the lower left corner. It is there to protect the delicate components of the power supply. By having the current go through the fuse first, the fuse acts as a gate to the rest of the device. If the current gets too high, the fuse breaks the connection, stopping flow of current to the power supply. This fuse is to assure that whatever circuit being measured does not damage the DMM.

Question 10: What is the difference between 2W and 4W resistor measurements?

The difference between them is that a 4W resistor measurement takes into account the small amount of resistance encountered by the measurement leads themselves. 2W resistor measurements do not account for this. Generally, the 2W method is used for higher resistances such as kΩ 's, while the 4W method is for lower resistances such as Ω's.


Question 11: How would you measure current that is around 10 A using DMM?

By connecting the Positive lead to the bottom right slot, to the right of the fuse, and the Negative lead in the slot directly above it. This is opposed to the regular orientation for the DMM, which has the Positive lead above the fuse. This is done to skip this particular fuse, as it would trip at a current of 10 A.

Thursday, January 12, 2017

Week 1:Intro to Circuits Lab







Part 1: 
Monday: Quiz Discussions & Weekly Lab Intro       
Mon-Wed (Outside of Class): Response to Comments    
Wed: Finishing Weekly Lab      
Fri: Blog Commenting & Blog Discussions          
Weekend Busy Work: Finish Blog Entries, Comment on 2 Blogs, & Take Home Quiz
           

Part 2: 
1. Do not work alone on live equipment.
2. Turn off power, discharge any charges, e.g. capacitors.
3. Touch live circuits with insulated probes, never touch a live circuit with your bare hands
4. Don't stand on conductive material.
5. Electricity and water don't mix. If there isn't a ground, you're the ground.
6. Don't put conductive material on your hands.
7. If it's a live circuit, just let it drop if it drops.
8. Use one piece of equipment at a time.
9. If the circuit is hot, don't touch it.
10. If something is generating a lot of heat, don't touch with your bare hands.
11. Certain parts(e.g. large wattage resistors)  have open metal pieces that are live.
12. Ask permission to start your circuit.


Part 3:
Current will kill if it is high enough. Between .1 amps and .2 amps of it with kill you. Above that will severely harm you and may even stop your breathing Below .1 and above .01 amps will hurt, shock, or make it hard to breath on the higher end of that scale.
Part 4:
Reading a resistors color code

Part 5:
Tolerance in a resistor is the allowed variation in resistance value from the color code value.
for example. one of our resistors color code was read as 2200 Ohms and a tolerance of 5% meaning that it could deviate by a value of  5% plus or minus from 2200 in this case 110. The 5% tolerance of this resistor is 2090 through 2310. The measured value was 2182 well within tolerance.

Part 6:

To prove that the resistors were within the tolerance range read the color codes and record the color code values with the tolerance. Then we used the multi-meter to measure the actual resistance of a given resistor. With the read value and the measured value it was then possible to tell if it was in tolerance by using the tolerance given from the read value and basic math.


Resistor
number
Read Value Tolerance Measured value Is in
tolerance?
1 180 5% 176 yes
2 150 5% 149.2 yes
3 2,700 5% 2,737 yes
4 390 5% 387 yes
5 2200 5% 2182 yes
6 67.1 ~ 680 n/a
7 20.2 ~ 1197 n/a
8 932 2% 2000 no
9 270 5% 271.3 yes
10 1500 5% 1,478 yes

Note:
for resistors 6, 7, and 8. We read the values wrong or the colors on them were just to faded to read.

Part 7:
When measuring Voltage with a digital multimeter you take the two leads and contact in parallel with what you are measuring. when measuring current you break where you want to mearure the circuit and measure then complete it again in series with the 2 leads to measure the current.



Part 8:
Our lab power supplies can supply 3 different voltages at a time thought 3 channels. One Fixed at 5 volts. Then an A and B channel. The A and B channels can each supply variable voltage from 0 to 24 volts.
Part 9:
Part 10:
To first prove Ohms law we used a 83.2 ohm resistor and applied five volts to it. We then measured the amperage though the resistor. We have now 83.2 ohms, 5v, 57.4 mA. Ohms law is V=IR so when we multiply 83.2*57.4 mA should get near 5 volts which we do with a value of 4.75 volts proving ohms law.

To prove ohms law experimentally though we used a single resistor and applied different voltages values to it instead of a single voltage. Again we measured the amperage though the resistor. This time we did Voltage/Current to get a resistance to prove ohms law.

Resistance Voltage Amperage  Voltage/Amperage
6710 0.655 0.0000908 7213.656388
6710 1.335 0.0002 6675
6710 1.918 0.00029 6613.793103
6710 2.417 0.00036 6713.888889
6710 3.78 0.00057 6631.578947

Part 11:
Rube Goldberg circuit

Part 12: 
Rube Goldberg circuit diagram






Part 13:
We could have a something like a ball or a domino knock a cover off of the photoresists to have the motor start spinning. The spinning motor could lift up a gate to let a ball roll down a ramp and trigger another circuit of the Rube Goldberg.