Blog #01: Basic Circuit and Measurement

2023-10-06 | By Alex Nguyen

This blog and the accompanying videos teach how to use important equipment and some electronic circuits. This blog acts more like a lab handout or an outline of the experiments for the video that goes beside it.

Videos

Blog #01: Basic Circuit and Measurement Part 1 Video above

Blog #01: Basic Circuit and Measurement Part 2 Video

Concepts

We need to go over some quick concepts before continuing on to the experiment. In the previous video, power was defined as the rate of which the electrical energy is being consumed or generated in an electrical circuit. Power is calculated as the product of current and voltage. Referring to the textbook "Electric Circuit 11th edition J.W Nilsson and S.A Riedel" which is used in the circuit classes at Washington State University, this book has a standard for the polarity of power. Following this textbook convention, a positive value represents absorbing power, and a negative value represents supplying power.

Using the digital multimeter or DMM for short, it is able to measure resistance, voltage, and current. To measure resistance, the resistor needs to be unpowered and isolated from the rest of the circuit. The DMM then would be connected directly across the resistor which is similar to a parallel connection.

For measuring voltage, the DMM would be connected in parallel to the electronic component that needs to be measured. The reason why this is done is because voltage is the electric potential difference. You would want the DMM to compare the two potentials.

For measuring current, the DMM would be connected in series to the circuit element that needs measuring. This generally involves breaking the circuit in order to add the DMM to it. The reason why this is done is because current is the flow of electric charges. When the DMM is connected in series then the DMM is able to see how many charges are flowing in a certain time frame. With these concepts over with, we can go on with the experiments.

Experiment #1

For the first experiment, the power supply would be set at 15V with a 4.7kΩ resistor, as shown in Figure 1.

Blog #01: Basic Circuit and Measurement Figure 1: A basic circuit with a single resistor.

Determine the color bands for the 4.7kΩ resistor with a 5% tolerance.

Blog #01: Basic Circuit and Measurement

Looking at the top of the parts kit, we can see that the color bands for that resistor is yellow, purple, red, and gold.

With the DMM, measure the value of the 4.7kΩ resistor and record it in the following table.

Blog #01: Basic Circuit and Measurement

The resistor was measured by placing the DMM leads across the resistor which was measured as 4.635kΩ.

Apply a 15V DC power supply onto the circuit and use the DMM to record the circuit values in Figure 2. Pay attention to the polarity of the DMM and the measured values.

Blog #01: Basic Circuit and Measurement Figure 2: A basic one resistor circuit with labeled current and voltage.

After grabbing the breadboard and inserting the resistor into it. Now turn on the power supply and set it to 15V, make sure the channel is turned off, and connect the power supply to the circuit.

Blog #01: Basic Circuit and Measurement

Now turn the power supply on and measure the voltage in the circuit, remember that voltage uses the same socket on the DMM as the resistance. Don't forget to press the voltage button on the DMM. To measure voltage, the DMM would have to be placed in parallel to our circuit element. It looks like the voltage is around 15.009V. Since we are done measuring the voltage, we can turn off the power supply to move on to the next circuit element.
Now it is time to measure the current in the circuit. Move the red lead on the DMM and plug it into the socket labeled as 100mA. Don't forget to press the current button. Now we can measure current by placing the DMM in series with the circuit element. This involves breaking the circuit to insert the DMM. With the power supply turned on, we can measure the current as 3.247mA. With all of the circuit elements measured, we can take the circuit apart.

Using the measured values from the previous table, calculate the power of each element and specify whether the power is absorbing or supplying. The textbook convention will be used where the positive value represents absorbing power and the negative value the supplying power.

Blog #01: Basic Circuit and Measurement

Using the values we recorded, we can calculate the nominal and measured powers. The equation for power is power is equal to voltage times current.
The nominal voltage is 15V and the nominal current is 3.19mA. Remember we are following the textbook "Electric Circuit 11th edition J.W Nilsson and S.A Riedel" for the polarity convention where positive represents absorbing power and negative represents supplying power. The nominal power for the power supply would be -47.8787mW and the resistor would be 47.8787mW.
The measured voltage is 15.009V and the measured current is 3.247mA. The measured power for the power supply would be -48.7342mW and the resistor would be 48.7342mW. The power supply would have supplied the power and the resistor would have absorbed the power.

Experiment #2

For the second experiment, the conservation of power law will be validated using a circuit with a power supply set to 15V and two resistors as shown in Figure 3.

Blog #01: Basic Circuit and Measurement Figure 3: A basic circuit with two resistors.

Determine the color bands for the 2.2kΩ resistor with a 5% tolerance.

Blog #01: Basic Circuit and Measurement

Looking at the top of the parts kit, we can see that the color bands for 2.2kΩ resistor is red, red, red, and gold.

Determine the color bands for the 1kΩ resistor with a 5% tolerance.

Blog #01: Basic Circuit and Measurement

We can also see that the color bands for the 1kΩ resistor are brown, black, red, and gold.

With the DMM, measure the value of the 2.2kΩ resistor and the 1k resistor. Then, record it in the following table.

Blog #01: Basic Circuit and Measurement

With the resistors found, we will use the DMM to measure the resistances and record them. The resistor is measured by placing the DMM leads across the resistor. R1 was measured as 2.182kΩ and R2 was measured as 1.018kΩ.

Apply a 15V DC power supply onto the circuit and use the DMM to record the measured values of the voltage source shown in Figure 4. Pay attention to the polarity of the DMM and the measured values.

Blog #01: Basic Circuit and Measurement Figure 4: A basic two-resistor circuit with currents and voltages labeled.

Now grab the breadboard and insert the resistors into it. To make the connections, we will be following the schematic as closely as possible to lessen confusion so R1 would be on the left and R2 on the right. We will use two wires in order to connect the tops of the resistors together and the bottoms of the resistors together. Make sure the power supply is turned on and is set to 15V. With the channel on the power supply turned off, connect it to the circuit.

Blog #01: Basic Circuit and Measurement

Remember that voltage uses the same sockets as resistance on the DMM. With the power supply's channel turned on, measure the voltage of the power supply by attaching the DMM in parallel to the power supply. Make sure the DMM is set to voltage and press the voltage button. The voltage of the power supply was measured as 15.003V. With that done, remove the DMM from the circuit and turn off the channel.
To measure current, the DMM needs to be added in series with the power supply. This involves the circuit needing to be broken. Move the red plug of the DMM into the other socket for current and press the current button. Turn the channel on. The current of the power supply was measured as 21.99mA. With that completed, turn off the channel. Remove the DMM from the circuit and reset the circuit.

Now measure the voltage across R₁ and the current through the resistor.

Blog #01: Basic Circuit and Measurement

To measure V1, we need to make sure the red wire is in the voltage socket and press the voltage button. After that, we can attach the DMM in parallel with R1. Make sure the DMM is set to measure voltage and the channel is on. V1 the voltage of R1 was measured as 15.003V. Turn off the channel on the power supply and remove the DMM's connection to the circuit.
Move the red plug of the DMM into the socket labeled for 100mA and press the current button. Break the circuit to add the DMM in series with R1. Turn on the channel. I1 which is the current through R1 was measured as 6.96mA. Turn off the power supply's channel and reset the circuit back to what it was before adding the DMM in.

Now measure the voltage across R₂ and the current through the resistor.

Blog #01: Basic Circuit and Measurement

Since we will be measuring voltage, make sure the red wire on the DMM is in the correct socket and press the voltage button. To measure V2, we need to attach the DMM in parallel with R2. Turn the power supply's channel on. The voltage across R2 was measured as 14.99V. Turn off the channel and remove the DMM from the circuit.
Move the red plug of the DMM into the other socket and press the current button. Break the circuit to add the DMM in series with R2. Turn on the channel. The current through the resistor R2 was measured as 15.23mA.

Using the measured values from the previous tables, calculate the power of each element and specify whether the power is absorbing or supplying. Remember that the textbook convention will be used where the positive value represents absorbing power and a negative value for the supplying power.

Blog #01: Basic Circuit and Measurement

We can calculate the nominal and measured powers using the values we recorded. Remember the equation for power is that power is equal to voltage times current.
For the power supply, the nominal voltage is 15V and the nominal current is 21.1mA. The measured voltage is 15.003V and the measured current is 21.99mA. Don't forget that we are using the textbook convention to represent polarity. This means that positive is absorbing power and negative is supplying power. The nominal power for the power supply would be -327.15mW and the measured power for the power supply would be -322.9mW.
For R1, the nominal voltage is 15V and the nominal current is 6.81mA. The measured voltage is 15.003V and the measured current is 6.96mA. The nominal power for R1 would be 102.15mW and the measured power for R1 would be 104.42mW.
For R2, the nominal voltage is 15V and nominal current is 15mA. The measured voltage is 14.99V and the measured current is 15.23mA. The nominal power for R2 would be 225mW and the measured power for R2 would be 228.29mW.
The power supply would have supplied the power and the resistors would have absorbed the power.