Day 8 (Thevenin lab)

Honestly if I invented something I would name it after myself too. The Carlos Munoz particle or maybe the Munoz technique. Anyway the class started by learning about the Thevenin theorem, which is extremely useful when you are unsure what kind of element will be added to your already complicated circuit and want a way to easily and quickly calculate how this new element will interact with your circuit. We first built this circuit in everycircuit and then we source transformed it to find its equivalent voltage and resistance across some unknown resistance. We found its thevenin voltage to be 30 volts and the thevenin resistance to be 4 ohms.

We did this again on a separate circuit seen here. The thevenin voltage and resistance was 40 volts and 20 ohms.

The lab Thevenin's theorem was a physical check to make sure that the theorem held true. In our pre-lab we determined that the thevenin resistance was 7.4 kiloohms and the thevenin voltage was .45 volts.

 

Here are pictures of the circuit that we built and the values that we obtained across the circuit.

Day 7 (Superposition lab)

The day started with a lab, Time Varying Signals. It was a precursor to the concept of linear propriety. The lab was very simple. Build a circuit that had a waveform generator and two resistors in series, they would have the same resistance value. Our pre-lab focused on those calculations. The signals should be 1 amplitude and .5 amplitude of the produced voltage.

Superman > Batman. *grabs popcorn*

Here are pictures of the circuit and the oscilliscope that agrees with our predictions at the set frequencies, voltages, and periods for all of generated waves.

Then we learned about linear propriety, which means that if some element multiplies by some constant then the change is linear relative to that constant. This circuit was used to illustrate this point. When the voltage source is 12 volts then the current becomes .316 amps and at 24 volts it becomes .189

Next the concept of superposition was introduced and the idea was very straight forward. A circuit can be analyzed, one independent source at a time and then the sum could be added up. This practice problem illustrates that. The current from the two sources added up to be 3 amps.

The Superposition 2 lab was an experimental test to prove that superposition was a circuit analysis technique that was accurate. The pre-lab starts by calculating what would happen if the circuit was built with all sources and we analyzed it using superposition. Here are pictures of the circuit when it had the 5 volt, the 3 volt, and both sources together; and our results.

Finally we learned about sources transformation and had an exercise on it. Here is the circuit shrunk down and the current we calculated was 2.31 amps.

Day 6 (BJT Curve Tracer lab) bjt incomplete

If nobody mentioned that there was a dirty version of the BBROYGBVGW memorization for resistors then I would definitely have learned a clean version. Unfortunately every time I want to read a resistor I have to go through bad boys doing UNSPEAKABLE things to young girls but Violet is unaffected by that. Anyway the class started by having students read resistor values for a set of unknown resistors.

We then learned about super meshes, which are branches that encompass current sources. We analyzed this circuit using that technique and found that the arbitrary currents had a value of -1.33, -3.07, and -.067 amps.

The lab that followed was an experimental test to prove that mesh analysis is a technique that gives a true assessment of a circuit. The pre-lab starts by calculating the theoretical value of a current and voltage drop at two specific points. The current going through the 10 kiloohm resistor is- .322 miliamps and the voltage drop on the 6.8 kiloohm resistor is five volts.

The circuit was built and the voltage measured was 4.97 volts and the current measured was -.34 miliamps. The percent error respectively was -.69% and 5.59%, which is pushing the limit of what is acceptable since these small circuits don't have a lot of places to introduce sources of error. Here are pictures of the circuit, the results, and the calculations.

Next was the concept of the BJTs and to understand how they worked we analyzed a circuit using mesh analysis. The two currents entering the BJT were 165 microamps and 8250 microamps and the voltage across the BJT was 5.175 volts. 

Last was the lab A BJT Curve Tracer, which was a nightmare to set up if you had the newest version of diligent. We used an older version and found that the beta of the BJT was about 37.5 and the base early voltage was around 1.5.

Day 5 (Nodal Analysis lab)

You don't need to wait until SUNDAY SUNDAY SUNDAY SUNDAY to learn about super nodes! A super node is actually two nodes that enclose a single voltage source and instead of writing an extra equation for both, the two can be combined and the currents entering that super node equal the currents exiting the super node. This technique was applied to a circuit and the arbitrary vx was equal to 30 volts.

The Nodal Analysis lab was just to experimentally prove that this technique does work and will give a correct interpretation of the circuit. In the pre-lab a circuit was analyzed using the nodal analysis technique. The voltages vary based on how much uncertainty the resistors have.

The circuit was then built and the experimental voltages were compared against the theoretical voltages. The experimental voltage drops for the 6.8 kiloohm and 22 kiloohm resistors were 2.43 and 4.41 volts respectively with percent errors of .413% and .22% respectively. Here are pictures of the circuit, the data, and the calculations.

The next circuit analysis technique that is introduced is mesh analysis. The concept is simple, each loop has some arbitrary loop current and then KVL is used to analyze the loop taking into account each of the arbitrary currents that affect each element in that loop. (I love this technique!)

This circuit was analyzed using mesh analysis and the loop currents were 1 amp and -2 amps, meaning that the direction was incorrect.

Day 4 (Temperature Measurement lab)

There was a quiz that morning and I would like to share pictures of myself right before, during, and after said quiz.

Right before

During

After

The quiz wasn't actually that bad. It was just a lot of variables to juggle around and using traditional KVL and KCL techniques to solve them were a little challenging for the allotted time. The quiz was a great lead to the new technique that we would learn but first was the lab.

The lab was the Temperature Measurement lab and it continued on the concept of a circuit that had sources dependent on external factors. This time it was a temperature probe (thermistor) that would adjust its resistance value based on the external temperature. With one constant resistor in series with the variable resistor, it was possible to measure a voltage and correlate that to a certain temperature.

In the pre-lab we were asked to find a resistor that would be placed in series with the thermistor to have a change in .5 volts when the thermistor goes from 25 to 37 degrees celsius. The resistor that we found accomplished this was 3500 ohms and it was expected that there would be a 1.25 difference in voltage. It was designed so that it was more accurate than the expected .5 volt difference.

 

The resistance of the thermistor at room temperature, roughly 25 degrees, was 10.48 kiloohms and at body temperature, roughly 35 degrees, the resistance was 6.34 kiloohms. The voltage across the resistor was measured at room temperature, roughly 25 degrees, as 1.26 volts and the voltage across the resistor at body temperature was 1.80 volts. The difference in voltages at the two different measurements was .527 volts which is significantly lower than the calculated value. Here is a picture of the set up, the results, and a video of the voltage change based on temperature.

The redesigned system of having a .1 volt/C change on the circuit proved to be mathematically impossible with resistors that had real values. The resistor would require some imaginary resistance.

The maximum change in voltage that this circuit can accomplish with this thermistor is .0457 volts.

A new circuit analysis technique that was introduced was the nodal analysis which set some essential node to a ground and then made arbitrary voltage values at every other essential node. Current was rewritten as differences in voltage over a resistance. This circuit was analyzed using nodal analysis. The arbitrary voltage values were 13.3 volts and 20 volts respectively.