Objectives - Basic Circuit

Electronic devices all share a fine level of control of electrical energy. This control happens through the electronic circuit. A circuit is a closed conductive path that allows electrons to flow and create an electric current. To create an electric current the circuit also needs an electrical energy source like a battery to start the flow of electricity.

Whereas a closed circuit allows current to flow, an open circuit has a break in the pathway which stops the current from flowing. An open circuit can be created by placing a switch along the circuit pathway. Any electrical device with an on/off switch creates a circuit which can be closed or opened.

In contrast to closed circuits and open circuits, a short circuit is usually not created by design. A short circuit happens when an unintended connection between two points in the circuit bypass the normal pathway. Because electrical current normally takes the path of least resistance, short circuits can cause too much current to overload components. This causes overheating and results in unsafe scenarios like melting wires, component failure, and the possibility of electrical fire.

The figure depicts a simple circuit using a battery to power a light-emitting diode (LED). In the figure, you see a circuit diagram, or schematic, that shows all the components of the circuit and how they are connected.

The battery supplies 3.7, 5 or 9 volts of direct current to the circuit. The plus sign near the battery symbol indicates the positive terminal of the battery. According to an early understanding of electricity known today as conventional current, electric current is positively charged, and flows from the positive terminal to the negative terminal. This is indicated in schematics that use conventional current by an arrow and the letter I. This labelling convention is still used today, even though it is now understood that the flow of current is the exact opposite: electric current flows from the negative terminal to the positive terminal and is made up of negatively charged electrons. Most schematics will use conventional current even though the flow of electrons is the opposite of what is shown. In this course, we will use conventional current to describe the flow of current but remember that, in actuality, the electron flow is the exact opposite.

The lines in the circuit diagram show how the circuit components are connected, using wire or other connectors. Electronic components are usually made with leads. Leads are protruding wires that connect to the inside of the component and provide the means to connect the component to other circuit elements.

The role of the resistor is to limit the amount of current that flows through the circuit. Resistance is measured in ohms (symbolized as Ω) and the resistor in this circuit helps to keep the LED from receiving too much current and being destroyed.

We can use led or lightbulb. The LED is symbolized by a triangle with a line segment on one end and two arrows pointing outward. The triangular part of the symbol represents a diode, and the two arrows facing out represent the fact that this diode emits light. Diodes are part of a special class of electronic components known as semiconductors.

An electronic circuit is shown with a 6V battery. An upward arrow pointing away from the positive side of the battery, a 2.2kohm resistor, and a symbol for an LED.

Examples:

●     Create a Simple Circuit using a 9V Battery as its Power Source

●     Create a Simple Circuit using a 1.5V Battery (AA or D Cell) as its Power Source

●     Series and Parallel Circuits

The components in an electrical circuit can be interconnected in different ways.

In a series circuit the components are interconnected one after another in a path between the positive and negative terminals of the power source, as shown on the left in the figure. The electric current travels through each component in a linear fashion. An example of a series circuit can be seen in a string of decorative holiday lights with each light connected to the next, one right after another.

In a parallel circuit, current flows from the battery terminal but splits at a junction which leads to parallel pathways through the circuit. Components connected along each pathway each get their own share of current, as shown on the right in the figure. In a parallel circuit you can power multiple components like LEDs. However, because each component gets its own supply of current, if any one component or LED were to fail, it would not stop the current from flowing to the other pathways and powering the other components or LEDs. In this way a parallel circuit could solve the common problem of a holiday string of lights, that when one light fails the circuit is opened and all of the lights go out.

While the decision between series or parallel circuits depends on the application, the power supply must be powerful enough to provide power to the entire circuit in both cases.

The figure shows 2 different types of circuits. The series circuit shows two light bulbs connected between a switch and a battery. The parallel circuit also shows two light bulbs connected between the switch and the battery, but they are not connected to each other. They connect to the switch and the battery independently.

Examples:

Practical exercises -  measurement of current, voltage and calculate the resistance.