In this project, we will build few simple LED Circuits. Nowadays, people are investing more in LEDs due to their energy efficiency. Home lighting, office lighting, Automobile lighting, Street lighting etc. are all being implemented using LED.
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Students, hobbyists and makers often work with LEDs in different types of projects. Some of the common LED projects are LED Running Lights, LED Light Bulb, LED Knight Rider and LED Flasher.
LEDs are very sensitive components with respect to voltage and current and they must be provided with rated current and voltage values. Beginners in electronics often start with LEDs and the first project would be blinking an LED.
Wrong voltage or current to LED will burn them off. For small projects like blinking an LED, we need not worry about burning LEDs as we can connect a small resistor (like a 330Ω) in series with the LED (for a 5V supply).
But as the complexity of the circuit increases, choosing the right resistor with right wattage is important. So, in this project, which is more of a tutorial, we will build some simple LED circuits like a simple single LED Circuit, LEDs in series, LEDs in parallel and high power LEDs.
Circuit 1 of Simple LED Circuits (Single LED Circuit)
The first circuit in the simple LED Circuits is a single LED Circuit. We will try to turn ON a single 5mm White LED using a 12V Supply. The circuit diagram for this circuit is shown below.
Components Required
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- 12V Power Supply
- 5mm White LED
- 330Ω 1/2W Resistor
- Connecting Wires
- Breadboard
Principle of Operation
The following image shows the setup of single LED connected to a 12V Supply and a current limiting series resistor. The important component (other than the LED of course) is the Resistor. Connecting a small LED to a 12V Supply would burn the LED and you can see the magic smoke instantly.
So, selecting the right resistor with the right wattage is very important. First, we will calculate the resistance.
Calculating Series Resistor
The value of the series resistor can be calculated using the following formula.
RSERIES = (VS – VLED) / ILED
Here, VS is the Source or Supply Voltage
VLED is the voltage drop across the LED and
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ILED is the desired current through the LED.
In our simple LED Circuit consisting of a single LED, we have used a 5mm White LED and a power supply of 12V.
As per the datasheet of the 5mm White LED, the Forward Voltage of the LED is 3.6V and the Forward Current of the LED is 30mA.
Therefore, VS = 12V, VLED = 3.6V and ILED = 30mA. Substituting these values in the above equation, we can calculate the value of Series Resistance as
RSERIES = (12 – 3.6) / 0.03 = 280Ω. Since there won’t be a 280Ω Resistor, we will use the next big resistor i.e. 330Ω. Hence, RSERIES = 330Ω.
Now that we have calculated the resistance of the series resistor, the next step is to calculate the power rating of this resistor.
Calculating Resistor Power
Power Rating of a Resistor specifies the value of power that a resistor can safely dissipate. The Power Rating of a Resistor can be calculated using the following formula.
PRES = VRES * IRES
Here, VRES is the voltage drop across the resistor and
IRES is the current through the Resistor.
We know that supply voltage is 12V and Voltage drop across LED is 3.6V. So, the Voltage Drop across the Series Resistor is
VRES = 12 – 3.6 = 8.4 V.
The current through the Resistor is same as the current through the LED as they are series. So, the current through the Series Resistor is
IRES = 30mA.
Substituting these values in the above formula, we get the power dissipated by the resistor.
PRES = 8.4 * 0.03 = 0.252 Watts.
To be on the safe side, we always have to pick the next possible value and hence we have chosen a ½ Watt (0.5 Watt) Resistor.
Once the right resistor is selected, we can connect the resistor in series and give the 12V Supply to the LED.
Circuit 2 of Simple LED Circuits (LEDs in Series)
The next circuit in the Simple LED Circuits project is connecting LEDs in series. In this circuit, we will connect three 5mm White LEDs is series with the same 12V Supply. The following image shows the circuit diagram of the LEDs in Series.
Circuit Diagram of LEDs in Series
Components Required for LEDs in Series
- 5mm White LEDs x 3
- 47Ω Resistor (1/4 Watt)
- 12V Power Supply
- Connecting Wires
- Breadboard
Principle of Operation
Since the LEDs are connected in Series, the current through all of them will be the same i.e. 30mA (for 5mm White LED). As three LEDs are connected in series, all the LEDs will have a voltage drop of 3.6V i.e. each LED will have a voltage drop of 3.6V across it.
As a result, the voltage drop across the resistor will fall down to 12 – 3*3.6 = 1.2V. From this, we can calculate the resistance as R = 1.2 / 0.03 = 40Ω. So, we have to choose 47Ω Resistor (the next available one).
Coming to the power rating of the resistor, it is equal to 1.2 * 0.03 = 0.036. This is a very low power rating and the minimum available one is of ¼ Watts.
Once all the components are selected, we can connect them on a breadboard and power on the circuit using a 12V Supply. All the three LEDs in Series will light up with maximum intensity.
Circuit 3 of Simple LED Circuits (LEDs in Parallel)
The final circuit in the simple LED Circuits tutorial is LEDs in Parallel. In this circuit, we will try to connect three 5mm White LEDs in parallel and light them up using a 12V Supply. The Circuit Diagram for LEDs in Parallel Connection is shown in the following image.
Circuit Diagram of LEDs in Parallel
Components Required for LEDs in Parallel
- 12V Power Supply
- 3 x 5mm White LEDs
- 100Ω Resistor (1 Watt)
- Connecting Wires
- Breadboard
Principle of Operation
Welger rp 200 service manual. For LEDs connected in Parallel, the voltage drop across all the LEDs will be 3.6V. This means that the voltage drop across the Resistor is 8.4V (12V – 3.6V = 8.4V).
Now, since the LEDs are connected in parallel, the current required for all the LEDs is equal to three times that of the individual current through the LED (which is 30mA).
Therefore, the total current in the circuit is 3 * 30mA = 90mA. This current will also flow through the resistor. Hence, the value of the resistor can be calculated as R = 8.4 / 0.09 = 93.33Ω. The nearest higher resistance value is 100Ω.
The Power dissipated by the resistor is given by 8.4V * 0.09A = 0.756Watts. As the next higher wattage is 1W, we have used a 1Watt Resistor.
Connect the three LEDs in Parallel and also connect the 100Ω (1 Watt) Resistor in series with the power supply. Up on turning on the supply, all the LEDs will light up.
Additional Circuits
- Here is a 23V0V LED Driver Circuit. In this circuit, we will drive an LED directly from 230V AC Mains Supply.
Warning: It is very dangerous to use 230V AC Supply on breadboard. Intellij idea 2018. Be extremely careful.
- Another interesting LED circuit is the DIY LED Light Bulb. In this, we designed an LED Light Bulb and used it as a regular bulb.
Warning: Even this project uses 230V AC for powering the LED Light Bulb. Be cautious when handling mains supply.
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In Time Management, after define activities process, activities that need to be performed to complete the project scope are determined. But, these activities must be performed in a sequence. What’s the reason for conducting this sequence activities process? Because some activities will depend on another, therefore they need to wait before the dependent activity finishes, some activities will start together and some activities will finish together. Therefore, the sequence of the project activities must be formed. This is mainly done with the help of Sequence Activities process.
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If you are thinking about making an application for PMP, in the PMP project management course you are enrolled in you will get a detailed explanation. So let’s explore what Sequence Activities process is, what is the best practice for implementing this process and finally illustrate for Sequence Activities process with a real-life project example.
What is It?
As defined in the PMP certification course, Sequence Activities is the process of identifying and documenting relationships among the project activities. So the main purpose of the sequence activities process is finalizing the interrelationship of activities to complete the project scope and reach the project goals.
The key result of the Sequence Activities process is Network Diagram. Network diagram of a project visualizes the project activities in boxes with activity ID and shows the interrelationship of activities with arrows. Now let’s briefly review this output of Sequence Activities process with a sample.
A Sample Network Diagram for Sequence Activities Process
This figure shows a sample network diagram as a result of sequence activities process.
As you see, after the start of the project,
- Activity #1 must start first.
- After Activity #1 finishes, Activity #2 and Activity #3 will begin.
- Activity #4 can start only after Activity #2 finishes.
- Activity #5 depends on Activity #2 and Activity #3, therefore, it will start only after these two activities are completed.
- And the last Activity, activity #6 can start only if Activity #4 and Activity #5 are completed.
- After activity #6 completion, the project will end.
Note that this is just a simple and sample network diagram in order to show you how a network diagram is. In real-life projects, there will be lots of project activities so the network diagram and also sequence activities process will be much more complex than this.
How to Create a Good Network Diagram in Sequence Activities process?
If the activity durations are added in the Network diagram during sequence activities process, the critical path of the project can be seen as well. A network diagram is a critical input to determine the critical path of the project and if activity durations are placed on these activity boxes, these will help in seeing the critical path of the project as well.
Precedence Diagramming Method which is abbreviated as PDM is the most common method to draw network diagrams. PDM is also referred as Activity-On-Node and abbreviated as AON. This is because the activities are represented as boxes or nodes in the network diagram.
In Precedence Diagramming Method boxes represent the activities of the project and arrows represent the dependencies of these activities.
For instance, in this figure above, Activity A is connected to Activity B with a forward arrow. This means, Activity B is depending on Activity A, and Activity B can start only after Activity A is finished. Or in other words, Activity A is the predecessor of the Activity B.
An Example for Sequence Activities Process
Now let’s see how sequence activities process can take place for a sample project. Let’s assume a sample project: Billing System Development for a utility service provider. We can define the activities of invoicing screen work package as analyze invoice screen requirements, the design of invoice screen, development of invoice screen and test of invoice screen.
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During sequence activities process, these activities must be planned in order to complete the project successfully. Activities will be starting from the beginning and will be ordered till the end.
The first two activities are analyzing invoice screen requirements and design invoice screen. The relationship between two activities is start-to-start plus 10 days. This means that design invoice screen activity can start only after 10 days passed after analyze invoice screen requirements started. This is a general approach in software development projects that, the design of the screens or features start after analysis comes to a level. Therefore, there is a time between each activity.
After the design of invoice screen activity is completed next activity: develop invoice screen can start. Development of the screen will be performed based on the design and analysis output. And there is a finish-to-start interrelationship between design invoice screen and develop invoice screen activities since the development of the screen cannot start before analysis and design are complete.
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Last activity is testing invoice screen. After the development, the screen must be tested before showing the final outcome to the customer or handing over to the customer. And if there are any bugs or problems with the screen, these must be fixed appropriately. Test of the invoice screen can start 2 days before the development finish date. Because, let’s assume that development of the screen takes 10 days, and after 8 days, it is expected that majority of the development is complete, and testing can start. In order to gain time in the project, testing can start 2 days before the development completion date.
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We explained the objective and the output of Sequence Activities process of Time Management. Sequence Activities process mainly aims to finalize the interrelationship of the activities for completing the project scope and for reaching the project goals.
Review by: Norman Steward