Simple Electronic Circuits for Beginners

Generally, success in early projects plays a vital role in the field of electronics for engineering students’ careers. Many students quit electronics due to failing in their first attempt. After a few failures, the student keeps a misconception that these projects working today might not work tomorrow. Thus, we suggest beginners start with the following projects which will give the output in your first attempt and gives motivation for your own work. Before you continue, you should know the working and usage of a breadboard. This article gives top 10 simple electronic circuits for beginners and mini projects for engineering students, but not for final year projects. The following circuits come under basic and small categories.

What are Simple Electronic Circuits?

The connection of various electrical and electronic components using connecting wires on a breadboard or by soldering on PCB to form circuits which are termed as electrical and electronic circuits. In this article, let us discuss a few simple electronics projects for beginners which are built with simple electronic circuits.

Simple Electronic Circuits for Beginners

The list of top10 simple electronic circuits discussed below are very helpful for the beginners while doing practice, designing of these circuits helps to deal with complex circuits.

DC Lighting Circuit

A DC supply is used for a small LED that has two terminals namely anode and cathode. The anode is +ve and a cathode is –ve. Here, a lamp is used as a load, that has two terminals such as positive and negative. The +ve terminals of the lamp are connected to the anode terminal of the battery and the –ve terminal of the battery is connected to the –ve terminal of the battery. A switch is connected in between wire to give a supply DC voltage to the LED bulb.

Rain Alarm

The following rain circuit is used to give an alert when it’s going to rain. This circuit is used in homes to guard their washed clothes and other things that are vulnerable to rain when they stay in the home most of the time for their work. The required components to build this circuit are probes. 10K and 330K resistors, BC548 and BC 558 transistors, 3V battery, 01mf capacitor, and speaker.

Whenever the rainwater comes in contact with the probe in the above circuit, then the current flows through the circuit to enable the Q1 (NPN) transistor and also Q1 transistor makes Q2 transistor (PNP) to become active. Thus the Q2 transistor conducts and then the flow of current through the speaker generates a buzzer sound. Until the probe is in touch with the water, this procedure replicates again and again. The oscillation circuit built in the above circuit that changes the frequency of the tone, and thus tone can be changed.

Simple Temperature Monitor

This circuit gives an indication using an LED when the battery voltage falls below 9 volts. This circuit is ideal to monitor the level of charge in 12V small batteries. These batteries are used in burglar alarm systems and portable devices. The working of this circuit depends on the biasing of the base terminal of the T1 transistor.

When the voltage of the battery is more than 9 volts, then the voltage on base-emitter terminals will be the same. This keeps both transistors and LED off. When the voltage of the battery reduces below 9V due to utilization, the base voltage of the T1 transistor falls while its emitter voltage remains the same since the C1 capacitor is fully charged. At this stage, the base terminal of the T1 transistor becomes +ve and turns ON. C1 capacitor discharges through the LED

Touch Sensor Circuit

The touch sensor circuit is built with three components such as a resistor, a transistor, and a light-emitting diode. Here, both the resistor and LED connected in series with the positive supply to the collector terminal of the transistor.

Select a resistor to set the current of the LED to around 20mA. Now give the connections at the two exposed ends, one connection goes to the +ve supply and another goes to the base terminal of the transistor. Now touch these two wires with your finger. Touch these wires with a finger, then the LED lights up!

Multimeter Circuit

A multimeter is an essential, simple, and basic electrical circuit, that is used to measure voltage, resistance, and current. It is also used to measure DC as well as AC parameters. Multimeter includes a galvanometer that is connected in series with a resistance. The Voltage across the circuit can be measured by placing the probes of the multimeter across the circuit. The multimeter is mainly used for the continuity of the windings in a motor.

LED Flasher Circuit

The circuit configuration of an LED flasher is shown below. The following circuit is built with one of the most popular components like the 555 timer and integrated circuits. This circuit will blink the led ON & OFF at regular intervals.

From left to right in the circuit, the capacitor and the two transistors set the time and it takes to switch the LED ON or OFF. By changing the time it takes to charge the capacitor to activate the timer. The IC 555 timer is used to determine the time of the LED stays ON & OFF.

It includes a difficult circuit inside, but since it is enclosed in the integrated circuit. The two capacitors are located on the right side of the timer and these are required for the timer to work properly. The last part is the LED and the resistor. The resistor is used to restrict the current on the LED. So, it won’t damage

Invisible Burglar Alarm

The circuit of the invisible burglar alarm is built with a phototransistor and an IR LED. When there is no obstacle in the path of infrared rays, an alarm will not generate buzzer sound. When somebody crosses the Infrared beam, then an alarm generated buzzer sound. If the phototransistor and the infrared LED are enclosed in black tubes and connected perfectly, the circuit range is 1 meter.

When the infrared beam falls on the L14F1 phototransistor, it performs to keep the BC557 (PNP) out of conduction and the buzzer will not generate the sound in this condition. When the infrared beam breaks, then the phototransistor turns OFF, permitting the PNP transistor to perform and the buzzer sounds. Fix the phototransistor and infrared LED on the reverse sides with the correct position to make the buzzer silent. Adjust the variable resistor to set the biasing of the PNP transistor. Here other kinds of phototransistors can also be used instead of LI4F1, but L14F1 is more sensitive.

LED Circuit

Light Emitting Diode is a small component that gives light. There is a lot of advantages by using LED because it is very cheap, easy to use and we can easily understand whether the circuit is working or not by its indication.

Under the forward bias condition, the holes and electrons across the junction move back and forth. In that process, they will get combine or otherwise eliminate one another out. After some time if an electron moves from n-type silicon to p-type silicon, then that electron will get combined with a hole and it will disappear. It makes one complete atom and that is more stable, so it will generate a little amount of energy in the form of photons of light.

Under reverse bias conditions, the positive power supply will draw away all the electrons present in the junction. And all the holes will draw towards the negative terminal. So the junction is depleted with charge carriers and current will not flow through it.

The anode is the long pin. This is the pin you connect to the most positive voltage. The cathode pin should connect to the most negative voltage. They must be connected correctly for the LED to work.

Simple Light Sensitivity Metronome Using Transistors

Any device that produces regular, metrical ticks (beats, clicks) we can call it as Metronome (settable beats per minute). Here ticks mean a fixed, regular aural pulse. Synchronized visual motion like pendulum-swing is also included in some Metronomes.

This is the Simple light sensitivity Metronome circuit using Transistors. Two kinds of transistors are used in this circuit, namely transistor number 2N3904 and 2N3906 make an origin frequency circuit. Sound from a loudspeaker will increase and is down by the frequency in the sound.LDR is used in this circuit LDR means Light Dependent Resistor also we can call it as a photoresistor or photocell. LDR is a light-controlled variable resistor.

If the incident light intensity increases, then the resistance of LDR will decrease. This phenomenon is called the photoconductivity. When lead light flasher comes to near LDR within a darkroom it receives the light, then the resistance of LDR will go down. That will enhance or affect the frequency of the origin, frequency sound circuit. Continuously wood keeps stroking the music by the frequency change in the circuit. Just look at the above circuit for other details.

Touch-based Sensitive Switch Circuit

The circuit diagram of the touch-based sensitive switch circuit is shown below. This circuit can be built with IC 555.in monostable multivibrator mode. In this mode, this IC can be activated by producing a high logic in reply to pin2. The time is taken for the generation of output mainly depends on the capacitor (C1) as well as variable resistor (VR1) values.

Once the touch plate is stroked, then the pin2 of IC will be dragged to a less logical potential like below 1/3 of Vcc. The output state can be returned from low to high on time to make the driver stage of triggering relay. Once the C1 capacitor is discharged, then the loads will be activated. Here the loads are connected to relay contacts and its controlling can be done through relay contacts.

Electronic EYE

The electronic eye is mainly used for monitoring the guests at the base of the door entry. Instead of calling bell, it is connected to the door with an LDR. Whenever an unauthorized person tries to unlock the door, the shadow of that person will fall over the LDR. Then, immediately the circuit will activate to generate the sound using the buzzer.

The designing of this circuit can be done using a logic gate like NOT using D4049 CMOS IC. This IC is inbuilt with six separate NOT gates but this circuit uses only single NOT gate. Once the NOT gate output is high & the pin3 input is less as compared with 1/3rd stage of the voltage supply. Similarly, when the voltage supply level increases above 1/3 then the output goes low.

The output of this circuit has two states like 0 & 1 and this circuit uses a 9V battery. The pin1 in the circuit can be connected to positive voltage supply whereas pin-8 is connected to the ground terminal. In this circuit, an LDR plays the main role to detect the person shadow and its value mainly depends on the brightness of shadow which falls on it.

A potential divider circuit is designed through 220 K Ohm resistor & LDR by connecting in series. Once the LDR gets less voltage in darkness then it gets more voltage from the voltage divider. This divided voltage can be given to as the NOT gate input. Once an: LDR gets dark & the input voltage of this gate reduced to 1/3rd of the voltage then pin2 gets high voltage. At last, the buzzer will be activated to generate the sound.

FM Transmitter using UPC1651

The FM transmitter circuit is shown below which works with 5V DC. This circuit can be built with a silicon amplifier like ICUPC1651. The power gain of this circuit is a wide range like 19dB whereas the frequency response is 1200MHz. In this circuit, the audio signals can be received using a microphone. These audio signals are fed to the second input of the chip through the C1 capacitor. Here, the capacitor acts like a noise filter.

The FM modulated signal is allowable at pin4. Here this pin4 is an output pin. In the above circuit, the LC circuit can be formed using an inductor and capacitor like L1 & C3 so that oscillations can be formed. Hereby changing the capacitor C3, the transmitter frequency can be changed.

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. 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 pin 3, and an input voltage through a switch is given to 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

 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 monostable 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.

Automatic Door Bell Ringer

Have you ever wondered? how easy it would be if you go to your home from the office, very tired and moved towards the door quite to close it. The bell inside rings suddenly, then someone opens the door without pressing.

You might be thinking that this looks like a dream or illusion, but it is not like that; it’s a reality that 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 phototransistor 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 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

Circuit Operation

The IR LED and the phototransistor is placed near such that, in normal operation, the phototransistor 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 the logic high signal, it is not triggered and the buzzer doesn’t ring, 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 phototransistor receives this reflected light and then starts conducting.

As this phototransistor conducts, the transistor gets biased and starts conducting too. 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.

Simple Rain Water Alarm System

Though rain is necessary for all, especially for agricultural sectors, at times, the effects 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 stuck us in heavy rain. The 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

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 the 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 rainwater is sensed, the buzzer starts ringing, giving an indication of the rain.

Flashing Lamps Using 555 Timer

We all love festivals, and therefore, be it Christmas or Diwali or any other festival – the first thing that comes to the mind is decoration. On such an occasion, can there be anything 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, here we are focusing on a simple flashing lamp circuit.

The basic idea here is to vary the intensity of the lamps at a frequency of one-minute intervals 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 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 pairs 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

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.

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 lifetime. 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

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 a very small amount of current, it conducts insignificantly. When this small amount of bias 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 that glows.

Simple Electronic Circuits for Engineering Students

There are several numbers of simple electronic projects for beginners that include DIY projects (Do It Yourself), solderless projects, and so on. The solderless projects can be considered as electronics projects for beginners as these are very simple electronic circuits. These solderless projects can be realized on a breadboard without any soldering, hence, termed as solderless projects.

The projects are Night light sensor, overhead water tank level indicator, LED dimmer, police siren, touchpoint based calling bell, automatic toilet delay lighting, fire alarm system, police lights, smart fan, kitchen timer, and so on are a few examples of simple electronic circuits for beginners.

Smart Fan

The fans are frequently used electronic appliances in residential homes, offices, etc., for ventilation and for avoiding suffocation. This project is intended for reducing wastage of electrical energy by automatic switching operation.

The smart fan project is a simple electronic circuit that gets switched ON when a person is present in the room and a fan gets switched OFF when a person leaves the room. Thus, the amount of electrical energy consumed can be reduced.

The smart fan electronic circuit consists of an IR LED and photodiode used for detecting a person. A 555 timer is used to drive the fan if any person is detected by IR LED & photodiode pair, then the 555 timer gets actuated.

Night Sensing Light

The night sensing light is one of the simplest electronic circuits to design and is also the most powerful circuit to save electrical power by the automatic switching operation of the lights. The most commonly used electronic appliances are lights, but it is always difficult to operate them by remembering.

The night sensing light circuit will operate the light based on the light intensity falling on the sensor used in the circuit. The light-dependent resistor (LDR) is used as a light sensor in the circuit which automatically turn ON & OFF the light without any support of human.

LED Dimmer

The LED lights are preferable as they are the most efficient, long life and consumes very low power. The dim feature of LEDs is used for various applications such as intimidating, decorating, etc. Even though LEDs are being designed for dim but to obtain better performance LED dimmer circuits can be used.

The LED dimmers are simple electronic circuits designed using a 555 timer IC, MOSFET, adjustable preset resistor, and high power LED. The circuit is connected as shown in the above figure and brightness can be controlled from 10 to 100 percent.

Touch Point-based Calling Bell

In our day-to-day life, we typically use many simple electronic circuits such as calling bell, IR remote control for TV, AC, etc., and so on. The conventional calling bell system consists of a switch to operate and which creates buzzer sound or indicator light on.

The touchpoint based calling bell is an innovative and simple electronic circuit designed for replacing the conventional calling bell. The circuit consists of a touch sensor, 555 timer IC, transistor and buzzer. If the human body touches the touch sensor of the circuit, then a voltage developed on the touch plate is used for triggering the timer. Thus, the 555 timer output goes high for a fixed time interval (based on the RC time constant). This output is used to drive transistor which in turn triggers the buzzer for that time interval and turns OFF automatically after that.

Fire Alarm System

The most essential electronic circuit for residence, office, every place in which there is a possibility of fire accidents is a fire alarm system. It is always difficult even to imagine a fire accident, so the fire alarm system helps to extinguish the fire or escape from fire accidents to reduce human loss and property loss as well.

The simple electronic project built using an LED indicator, transistor, and thermistor can be used as a fire alarm system. This project can be used even for indicating high temperatures (fire causes high temperatures) such that the cooling system can be turned ON to reduce the temperature to a limited range. The thermistor (temperature sensor) is used for identifying changes in temperature and thus alters the transistor input. Thus, if the temperature range exceeds the limited value, then the transistor will turn ON LED indicator to indicate high temperature.

This is all about the top 10 simple electronic circuits for beginners who are interested in designing their simple electronic circuits. We hope these types of circuits will be helpful for beginners and also engineering students, Furthermore, any queries regarding electrical and electronics projects for engineering students, please give your feedback by commenting in the comment section below. Here is a question for you, what are active and passive components?

Photo Credits:

• Electronic Circuits electronicsandyou
• Simple Temperature Monitor electroschematics
• Touch Sensor Circuit build-electronic-circuits
• LED Flasher Circuit blogspot
• Invisible Burglar Alarm wordpress
• LED Circuit build-electronic-circuits