How to Build a Simple Electronic Project: LED Indicator Light

How to Build a Simple Electronic Project: Led Indicator Light

LED Indicator Light in its entirety is simply a light that blinks to indicate or register an event. It is like the electronics basics when it comes to design for safety. To be able to build a simple LED indicator light, one has to know that the ultimate goal of it all is to get the Lighting Emitting Diode (LED) to blink. This in actual sense can be done in various ways. For example, you can decide to use a relay, a transistor and even an inverter (micro-controller or a 555 timer). So to provide you with more than one option of building this simple electronic project, I will take you through these three methods. But first, let’s discuss the main component of this project; Light emitting diode (LED).

What is LED?

The LED is a two-lead light source semiconductor that was designed and developed by Nick Holonyak who as at 1962 was working for GE (General Electric). It is similar with the typical diode type as it has the same PN junction characteristics that a diode has. This makes it possible for it to allow current to flow in the forward direction and blocks the current in the reversed direction. LED in terms of sizes, LED lights occupies the small area below 1 mm2. Ever since its discovery, it has found application in various appliances that in all honesty cannot be counted. For this project, we will be using LED light as an indicator. You might want to know the exact thing we are indicating but then if we start with the applications of what we are about to build, we might never finish. To mention a few though;

  • In motor vehicles and bicycle lights.
  • In traffic light Indicators, signs and signals.
  • In data displaying boards.
  • In medical applications and toys
  • Non visual applications.
  • In light bulbs and many more.
  • Remote controls

Building an Led Indicator Light

Like I emphasized earlier, we will be building our LED indicator light by using three different approaches.

Using Relays

Relays are switches that are controlled by electric circuits. Depending on the design that you want, you might want to consider two ways in which you can use relay to achieve our goal of building an LED indicator light. But first, the list of components/materials needed;

  • 9V Battery
  • Relay (DS2Y-S-DC5V)
  • LED Bulb
  • Resistors (330ohms and 100ohms)
  • Capacitor

As shown in the circuit diagram above, the simple electronic circuit contains the components that are listed. To understand the whole concept of the circuit, you have to understand that the relay coil as shown above has active power that is supplied by the battery. In a switching situation; with the aid of the electromagnetic characteristics will disconnect this power from the electromagnet and supply the power to the LED bulb. However, when the relay no longer has power, it will switch again, turning off the power from the LED bulb and supplying it back to the electromagnet. This is the basis of the circuit and it goes on and on in cycles.

NOTE: This circuit has a problem; you will have to be faster than the speed of light to notice the LED blink as relay switch can be less than a second. So I call this particular design the Flash LED indicator light. And this will now lead us to the second stage of this design; solving the problem through the introduction of time-delaying components that will enable you see the LED light.

As seen in the circuit diagram above, two resistors (R1 and R2) are introduced alongside a capacitor. When power is applied to this circuit, the capacitor gets charged through R2. After which the coil of the relay is pulled into the other this instance, the LED bulb will turn on and the charge capacitor will now hold the relay in place, preventing it from switching again. But it is just a capacitor right? It will discharge in no time, time that is long enough for an observer to actually notice the blink. After the capacitor is discharged, the relay thereafter returns to its original state; turning the LED bulb off.

Using Transistors


  • 9V Battery
  • Resistors (Check the diagram below for ratings)
  • 10uF Capacitors (2)
  • LED Bulb (2)
  • Transistors

Hold on… I know the circuit diagram above might look all complex and all but really, it isn’t as complex as it looks. The diagram above is called an Astable Multivibrator and in order to fully understand the operational principles, you will need to understand Ohm’s law; that is the relationship between voltage, current and resistance. To keep it simple, I will explain the basics;

The two capacitors C1 and C2 are passive components and they alternate between being discharged and charged. A charged capacitor will turn a transistor ON and a capacitor that is discharged will turn it off. In a case when a transistor is turned ON, current will flow through it, making the LED bulb to light up.

The two capacitors C1 and C2 will alternate between being charged and discharged and thereby turning the transistors ON and OFF. When a transistor is ON it allows current to flow through it so that the LED above it will light up.

Using an Inverter

This is actually my personal favorite. It is easy and the number of components is not as much as the other ones discussed above. You need at most five (5) components;

  • Resistors
  • 9V Battery
  • LED Bulb
  • Inverter
  • Capacitor

Technically speaking, what an inverter does is to produce an output that is completely opposite of what it gets. For example, if there is an input of low voltage, the inverter will give an output of high voltage. Don’t forget that a high voltage doesn’t necessarily means HV in power systems. As far as electronics is concerned, a high voltage is a voltage that is approximately equal to the supply voltage and a low voltage on the other hand is a voltage that is approximately equal to zero.

You can see in the circuit diagram that the inverter output (U1) is connected with a resistor back to the input. This means that the output will be low if there is a high voltage on the input. But the input will be low since the output is connected back to the input. Now, with low input, the output is going to be high. That means the input is going to be high again, and so on… So it’s going to keep jumping up and down.

A capacitor on the inverter’s input is used to slow down the jumping back and forth. The R1 resistor controls how much current return to the input capacitor. Therefore, the blinking speed will be determined by the size of the resistor R1 and the capacitor C1. The inverter I’ve used is an inverter from Schmitt Trigger. Schmitt Trigger simply means that the switching threshold from high to low differs from the switching threshold from low to high.

This brings us to the end of the simple electronic project. You can always choose anyone you want to use but do not forget the basic precautions to be taken if you are to build any one of them. One of those instructions that I love so well is; safety first. Ensure you use the right component and when testing, do not be discouraged if it seems not to work. Sometimes a mistake as small as polarity misplacement can cause your circuit not to work so ensure that your components are well connected. Lastly, have it in mind that what we built is a LED indicator light. We didn’t in anyway discuss the application principles of this work so I’ll advice you simply master it first before thinking of applying in another circuit.