CCIT4076 Engineering and Information Science

Laboratory 1: Basic Electric Circuit

HKU SPACE Community College, Fall 2022

1        Introduction

In this laboratory we will build a simple electric circuit to light an LED bulb up on a breadboard. Specifically, we will use the components introduced in week 2 to prototype a simple closed circuit. We will also take some physical measurements to equip you with some feelings on what is voltage, current and resistance.

2        Components

The list of components used in this lab are:

• Power Supply (we will stick with 4.5 volt)
• Breadboard
• 330 Ohm Resistors
• LED light bulb
• Digital Multimeter

Figure 1: Components to be used in this lab.

3        Procedures

Listen carefully to your lecturer’s instructions on

1. How to connect your power supply to the breadboard;
2. How to wire the supply pins to the Voltage common connector (VCC) bar and the GND bar

Then, carefully study the following figure:

Question. Before you go on, point out what is wrong on the following connection:

4        Experiments

4.1        Lighting Up an LED Bulb

The first experiment we shall conduct to simply wire the following circuit:

Figure: Target Circuit

and if you have followed everything strictly, the schematic can be translated as:

Figure: Illustration

whereas the LHS bar is the GND voltage; the RHS bar is the VCC voltage.  

4.2        Measuring Electric Properties

Next, we will make use of the multimeter to measure current and voltages over different circuit components. Since the multimeter is not a robust device, you must read the following passage very carefully before moving on. Otherwise, you are placing your multimeter at very high risk of malfunctioning.  

4.2.1        Measuring Voltage

The multimeter is multi-purpose. In this subsection, you should choose the voltmeter mode. This is visualized in the figure below. Under such mode, you are allowed to test the voltage difference between any TWO nodes over the circuit. Your tasks are as follows:

1. Measure the Voltage difference across the 330 ohm resistor
2. Measure the Voltage across the LED Bulb
3. Measure the Voltage across the Vcc bar and the GND bar

Figure: Multimeter under the Voltmeter mode.

4.2.2        Measuring Current

In this subsection, you should choose the ammeter mode. This is visualized in the figure below.

Figure: Multimeter under the Ammeter mode.

Under such mode, you are allowed to test the current passing through any ONE node over the circuit. Specifically, you should rewire the circuit on breadboard by the schematic:

Figure: Schematic with the Ammeter Wired Properly.

The ammeter should NOT be connected directly. Instead, you should first break the circuit by disconnecting the resistor from the LED bulb, and then plug that shorter leg to another row on the breadboard (you should see the bulb switched off at this moment). Next, use the red pin needle to touch the row connecting the 330 ohm resistor, and use the black pin needle to touch the row connecting the shorter leg of the LED bulb; pictorially:

Figure: Illustration of how to properly connect the ammeter. [source]

The Instructor will perform a demonstration on how to properly measure the current flowing through this circuit.