Know About How to Build a Simple Electronic Circuits

Most of the students are interested to do the Do It Yourself kits or circuits development by their own hands with use of some circuit simulation software’s. We feature an extensive collection of simple electronic projects; these projects are more beneficial for many engineering students from basics to advanced level. These all circuits are 555 timer based circuits developed and simulated in multisim software with verified output. So lets look on them.

1. Automatic Washroom Light

Have you ever thought of any system ever existed that is capable of switching on the lights of your washroom the moment you enter into it, and switching off the lights when you leave the bathroom?

Is it really possible to switch on the bathroom lights by just merely entering the bathroom and switch off by just leaving the bathroom? Yes, it is! With an automatic home system you don’t really need to press any switch at all, on the contrary, all you need to do is open or close the door – that’s all. In order to get such a system all you required is a normally closed switch, an OPAMP, a timer and a 12V lamp.

Components Required

Circuit Connection

The OPAMP IC 741 is a single OPAMP IC consisting of 8 pins.The Pins 2 and 3 are the input pins while the pin 3 is a non-inverting terminal, and the pin 2 is an inverting terminal. A fixed voltage through a potential divider arrangement is given to the pin 3,and an input voltage through a switch is given to the pin 2.

The switch used is normally closed SPST switch. The output from the OPAMP IC is fed to the 555 Timer IC, which if triggered (by a low voltage at its input pin 2), generates a high logic pulse (with the voltage equal to its power supply of 12V) at its output pin 3. This output pin is connected to the 12V lamp.

Circuit Diagram

Automatic Washroom Light
Automatic Washroom Light

 Circuit Operation

The switch is placed on the wall in such a way that when the door is opened by pushing it completely towards the wall, the normally closed switch gets opened when the door touches the wall. The OPAMP used here works as a comparator. When the switch is opened, the inverting terminal gets connected to the 12V supply, and a voltage of approximately 4V is fed to the non- inverting terminal.

Now, the non-inverting terminal voltage being lesser than that at the inverting terminal, a low logic pulse is generated at the output of the OPAMP. This is fed to the timer IC input through a potential divider arrangement.  The timer IC gets triggered with a low logic signal at its input and generates a high logic pulse at its output. Here, the timer works in a mono- stable mode. When the lamp receives this 12V signal, it glows.

Similarly, when a person comes out of the washroom and closes the door, the switch gets back to its normal position and gets closed. Because the non-inverting terminal of the OPAMP is at a higher voltage compared to the inverting terminal, the output of the OPAMP is at a logic high. This fails to trigger the timer; since there is no output from the timer, the lamp gets switched OFF.

2. Automatic Door Bell Ringer

Have you ever wondered how easy it would be if you go to someone’s place, and the person there opens the door without you even pressing the bell,or if you have reached your home from office,very tired and moved towards the door quite close to it, and the bell inside rings suddenly, and then someone opens the door, and you enter without even pressing the door bell.

You might be thinking that this looks like a dream or illusion, but it is not like that; it’s a reality which can be achieved with a few basic electronic circuits. All that is needed is a sensor arrangement and a control circuit to trigger an alarm based on the sensor input.

Components Required

Circuit Connection

The sensor used is, an IR LED and a photo transistor arrangement,placed adjacent to each other. The output from the sensor unit is fed to the 555 Timer IC through a transistor and a resistor. The input to the timer is given to the pin 2.

The sensor unit is supplied with a voltage supply of 5V, and the timer IC pin 8 is supplied with a Vcc supply of 9V. At the output pin 3 of the timer, a buzzer is connected. The other pins of the timer IC is connected in a similar manner so that the timer operates in a mono-stable mode.

Circuit Diagram

Automatic Door Bell Ringer
Automatic Door Bell Ringer

Circuit Operation

The IR LED and the photo transistor are placed near such that, in normal operation, the photo transistor doesn’t receive any light and doesn’t conduct. Thus, the transistor (as it doesn’t get any input voltage) doesn’t conduct.

Since the timer input pin 2 is at logic high signal, it is not triggered and the buzzer doesn’t rings, as it doesn’t receive any input signal.If a person approaches the door, the light emitted by the LED is received by that person and gets reflected back. The photo transistor receives this reflected light and then starts conducting.

As this photo transistor conducts, the transistor gets biased and starts conducting too.The pin 2 of the timer receives a low logic signal and the timer gets triggered. As this timer gets triggered, a high logic pulse of 9V is generated at the output, and when the buzzer receives this pulse, it gets triggered and starts ringing.

3. Simple Rain Water Alarm System

Though rain is necessary for all, especially for agricultural sectors, at times, the affects of rain are devastating, and even many of us often avoid rain with a fear of getting drenched, particularly when the rain is heavy.Even if we are confined ourselves inside the car, a sudden heavy downpour restricts and stucks us in heavy rain. Operating vehicle’s windshield under such circumstances becomes quite a troublesome affair.

Therefore, the need of the hour is to have an indicator system that can indicate about the possibility of rain. The components of such a simple circuit include an OPAMP, a timer, a buzzer, two probes, and of course, a few basic electronic components. By placing this circuit inside your car or home or anywhere else, and the probes outside, you can develop a simple system for detecting rain.

Components Required

Circuit Connection

The OPAMP IC LM741 is used here as a comparator. Two probes are provided as input to the inverting terminal of the OPAMP in such a way that when rain water falls on the probes, they get connected together. The non-inverting terminal is supplied with a fixed voltage through a potential divider arrangement.

The output from the OPAMP at pin 6 is given to the pin 2 of the timer through a pull-up resistor. The Pin 2 of the timer 555 is the triggering pin. Here, the timer 555 is connected in a mono-stable mode such that when it is triggered at the pin 2, an output is generated at pin 3 of the timer. A capacitor of 470uF is connected between the pin 6 and the ground, and a capacitor of 0.01uF is connected between the pin 5 and the ground. A resistor of 10K ohm is connected between pins 7 and Vcc supply.

Circuit Diagram

Simple Rain Water Alarm System
Simple Rain Water Alarm System

Circuit Operation

When there is no rain, the probes are not interconnected (here key button used in place of probes), and hence, there is no voltage supply to the inverting input of the OPAMP. As the non-inverting terminal is provided with a fixed voltage, the output of the OPAMP is at a logic high signal. When this signal is applied to the input pin of the timer, it is not triggered and there is no output.

When rain starts, the probes get interconnected by the water droplets as water is a good conductor of current, and therefore,current starts to flow through the probes, and a voltage is applied to the inverting terminal of the OPAMP. This voltage is more than the fixed voltage at the non-inverting terminal – and then, as a result, the output of the OPAMP is at a logic low level.

When this voltage is applied to the timer input, the timer gets triggered and a logic high output is generated, which is then given to the buzzer. Thus, as rain water is sensed, the buzzer starts ringing, giving an indication of the rain.

4. Flashing Lamps Using 555 Timer

We all love festival, and therefore, be it Christmas or Diwali or any other festival – the first thing that comes to the mind is decoration. In such an occasion, can there be any thing better than implementing your knowledge of electronics for the decoration of your house, office or any other place. Though there are many types of complex and efficient lighting systems, but here we are focusing on simple flashing lamps circuit.

The basic idea here is to vary the intensity of the lamps at a frequency of one minute interval, and to achieve this, we have to provide oscillating input to the switch or the relay driving the lamps.

Components Required

Circuit Connection

In this system, a 555 timer is used as an oscillator that is capable of generating pulses at a maximum of 10 minutes time interval. The frequency of this time interval can be adjusted by using the variable resistor connected between the discharge pin 7 and the Vcc pin 8 of the timer IC. The other resistor value is set at 1K, and the capacitor between the pin 6 and pin 1 is set at 1uF.

The output of the timer at pin 3 is given to the parallel combination of a diode and the relay. The system uses a normally closed contact relay. The system uses 4 lamps: two of which are connected in series,and the other two pair of series lamps are connected in parallel to each other.  A DPST switch is used to control the switching of each pair of lamps.

Circuit Diagram

Flashing Lamps Using 555 Timer
Flashing Lamps Using 555 Timer

Circuit Operation

When this circuit receives a power supply of 9V (It can be 12 or 15V as well), the timer 555 generates oscillations at its output. The diode at the output is used for protection. When the relay coil gets pulses, it gets energized.

Suppose the common contact of the DPST switch is connected in such a way that the upper pair of lamps receives the supply of 230 V AC. As the switching operation of the relay varies due to oscillations, the intensity of the lamps also varies and they appear flashing. The same operation occurs for the other pair of lamps as well.

5. Battery Charger Using SCR and 555 Timer

Nowadays all the electronic gadgets you use depend on the DC power supply for their operations.They usually get this power supply from the AC power supply at homes, and use a converter circuit to convert this AC to DC.

However,In case of a power failure, it is feasible to use a battery. But, the main problem with the batteries is their limited life time. Then, what should be done next? There is a way as you can use rechargeable batteries. Next, the biggest challenge is the efficient charging of the batteries.

To overcome such a challenge, a simple circuit using SCR and a 555 timer is designed to ensure controlled charging and discharging of the battery with indication.

Circuit Components

Circuit Connection

A 230V power is supplied to the primary of the transformer. The secondary of the transformer is connected to the cathode of the Silicon Control Rectifier (SCR). Next, the anode of the SCR is connected to a lamp, and then, a battery is connected in parallel. A combination of two resistors (R5 and R4) is then connected in series with a 100Ohm potentiometer across the battery. A 555 timer in a mono-stable mode is used,and it gets triggered from a series combination of a diode and a PNP transistor.

Circuit Diagram

Battery Charger Using SCR and 555 Timer
Battery Charger Using SCR and 555 Timer

Circuit Operation

The step-down transformer reduces the AC voltage at its primary, and this reduced AC voltage is given at its secondary. The SCR used here acts as a rectifier. In normal operation, when the SCR is conducting, it allows the DC current to flow to the battery. Whenever the battery is charged, a small amount of current flows through the potential divider arrangement of R4, R5, and the potentiometer.

As the diode receives very small amount of current, it conducts insignificantly.When this small amount of biasing is applied to the PNP transistor, it conducts. As a result, the transistor is connected to the ground, and the input pin of the timer is given a low logic signal, which triggers the timer. The output of the timer is then given to the Gate terminal of the SCR,which is triggered to conduction.

If the battery is fully charged, it starts discharging and the current through the potential divider arrangement increases, and the diode also starts conducting heavily, and then the transistor is in cut off region. This fails to trigger the timer, and as a result, the SCR is not triggered and this stops the current supply to the battery. As the battery charges, an indication is given by a lamp which glows.

This is all about a few simple electronic project ideas for all those individuals who are interested in building their own electronic projects. We hope this type of projects and project ideas will be helpful to the students, and therefore, if anyone of the project catches your attention or to know how to step up the DC voltage using 555 timer, which is enough to implement it, do give your comments, feedback and suggestions to us,and also write to us about the kind of changes you can bring in to those projects using your own ideas.

4 Comments

  1. Ekoh George Gio says:

    I love this site

      1. thanks for sharing information.

        1. Tarun Agarwal says:

          Hi Sam,

          Please check the user friendly website http://www.edgefxkits.com for the latest projects on Electronics. You can download project abstract and seminar presentation also.

          Raji (Mobile: +91 9959178000)

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