Day 11

Summing and Difference Amplifiers

Further experimentation of Op Amps. The objective of the first portion of the lab is to model a suming amplifier and to analyze it in an actual circuit. Ideal summing amplifiers have a relationship between Vin and Vout.

 Using nodal analysis we get the following equation.

 Here we designed a circuit that would fulfill the parameters of the experiment. Our goal was to be able to plot Vout while remaining in the linear region without hitting saturation.

 Below is the circuit of our designed circuit.

3/26/15 (Week 5)

Inverting Voltage Amplifier

Here we are understanding operational amplifiers (op amps). Op Amps perform multiplications by a negative constant. Here is an example of a circuit diagram that includes the OP 27 and its representation in the circuit. 

 This is our experimental data for the feedback resistance and the input resistor. The ratio is very close to the theoretical value.

 Below is the circuit of the above circuit diagram using an OP Amp. We connected the OP Amp across the bridge of the breadboard which makes designing a circuit on the breadboard very convenient. 

 Here we measured and plotted the Vin vs Vout. The graph of the data demonstrates the properties of the Op Amp because we see the amp saturates when approaching the supply rail voltages. It is also inverted from the input voltages.

Op Amps are a new concept introduced to us in class. They behave differently depending on the circuit built around them.

3/24/15 (Week 5)

Maximum Power Transfer and Non-Ideal Power Sources

We get a transfer of maximum power when the resistances inside the voltage source is ideal (a resistance of zero). This is what we call an ideal power source, but in reality all voltage sources will have internal resistances.

Here we are trying to maximize the power delivered to our load resistor.

 Here we have our measured values for the power delivered.

 Comparing our theoretical and experimental values we yield very little error.

 To conclude our experiment, voltage sources will have internal resistances and we need to use these real world conditions when constructing our circuits. Now we have a better understanding of non-ideal power sources.

03/19/15 (Week 4)

Thevenin's Theorem

We experimented with Thevenin's Theorem. We found the Thevenin equivalent circuit of our given circuit diagram. 

Here is the construction of the above circuit. Thevenin's theorem allows us to recalculate certain elements of the circuit without having to resolve the entire circuit equations.

As we found the theoretical Thevanin equivalents, we know need to find it experimentally. Our experimental data was only 1 micro-Amp from the theoretical value.

Here we find the equivalent resistance. Again our theoretical and experimental values were very close in values.

 Now we used potentiometers for the resistors so we can change the values and see if the Thevanin theorem holds true.

 Our collected data using different resistances with the potentiometers.

 This is the graph of Power vs. Load Resistance of our experiment.

03/17/15 (Week 4)

BJT Curve Tracer

Here we analyzed the collector current vs collector voltage of a BJT. Our focus was to see the behavior of the BJT when given a step voltage source and a triangle voltage supply. Here we predicted what Vout would be for each given voltage divider.

This is our circuit which consists of a 100 ohm resistor, a 100k resistor, two voltage sources, and our volt meter.

The two setups for the variable voltages supplied to the circuit.

 Here we collected the data for the output and input voltages.

This is the extracted data where we plotted it. We can see that the graph is almost identical to the above graph from Waveforms. This lab was hard to analyze as we didn't have the skill set or knowledge to understand the setup and the reasons for the testing.

3/12/15 (Week 3)

Quiz

Using Mesh Analysis

Here we learned about Super Meshes.

Here we learn how to redraw a transistor using elements we already have knowledge of.

Mesh Analysis III

Here we are using Mesh Analysis to solve a circuit.

Now we are going to get experimental data to see how close our Mesh Analysis calculations were.

Turns our Mesh Analysis worked wonderfully with a very low error of 3.8% and 0%.

 The error of 3.8% could be due to temperature of the room not being ideal.

03/10/15 (Week 3)

Nodal Analysis

Using Nodal Analysis to solve "Supernodes". By doing this we relate all voltages to a "ground" node. In doing so we can come up with a system of equations in which to solve for certain elements in the circuit. For this pre-lab we find the theoretical values of the voltage across each of the resistors.

Now it's time to test the results in our pre-lab. We will create the above circuit and measure each of the voltages across the resistors.

 With Nodal Analysis we were able to find the voltages across each of the resistors with 1% or less of error. This 1% of error most likely arose from the fact that our voltages across every area were off by plus or minus 1%. For example, the voltage across the voltage source 3V was actually 2.99V. Our measuring instrument could also add a small error of uncertainty. However, this was an excellent experiment.

03/05/15 (Week 2)

Quiz 1

In class today we learned how to use nodal analysis to solve a circuit by creating a system of equations and solving for the missing variables. 

Temperature Measurement System

In this experiment we are testing how temperature changes the resistance within a resistor. In the circuit diagram we get a resistor that is a control, which will not change temperature. We then find which resistors to use to get a voltage change of at least 0.5 volts. Once we find these calculations we can test this experimentally.

Here we set up Analog Discovery to the above circuit with the two resistors we calculated.

It turned out that our measured value for resistors didn't give us the voltage change we desired. We only got a voltage change of 0.43 volts. This is real world engineering, we needed to use a 4.3 kOhm resistor but they don't exist. So we stepped up the resistance to 4.7kOhms. Since we fell short we decided to step down the voltage to 3.9kOhm. This made our change in voltage even lower. So for attempt number 3 we stepped up the voltage to 5.6kOhm. Here we got a voltage change of 0.51 volts which is what we were looking for.

Our calculated values didn't quite work out in the real world perspective. We needed to step up the resistor from 4.3kOhm to 5.6kOhm. That is quite a jump in resistance. One of the contributing factors to this is that we assumed that the room was 22 degrees Celsius and our finger tips were at average body temperature. But in reality the room was probably colder and our finger tips were also colder than average body temperature. So we calculated what change in voltage the new resistors would have given us. It turns out it was still only 5.5% off.

03/03/15 (Week 2)

Creating a Night Light and the Hot Dog Circuit

Here we have a hot dog circuit. The LEDs run in series with the hot dog while other LEDs run in parallel. The circuit slowing burned and cooked the hot dog.

Here is a night light using a photocell, a BJT transistor, and an LED. The photocell changes its resistance depending on the light received. With lots of light we have a low resistance and via versa. the BJT was used to step down current to the necessary value required for the LED to light up. 

 Our constructed circuit using the photocell for the LED. We will now change how much light goes into the photocell.

 As we reduce the amount of light the photocell receives we get the LED to light up.