Lithium Ion battery is now used in many devices. Unlike other batteries, in Lithium Ion battery, the charge level is expressed as percentage. Its minimum voltage is 3.6 V and maximum voltage is 4.2 V. It is the fully charged state. You can Monitor the charging of 18560 Lithium Ion battery using this circuit.

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School Project 7. Here is a high efficiency Wireless Electricity Generator project. Usually, we make a simple wireless electricity generator to light 1.8 volt Red LED. But here the efficiency of the wireless electricity is increased to light 1 watt White LED. It generates voltage and current even to light a Strip LED. Try it and see the wonder of LED lighting without a battery connection.

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School Project 6. Simply touch Point A to turn on LED and point B to turn off LED. Points C and D can be used to connect Relay to drive AC loads like Bulb and Fan.

Note Touch pads can be small metal plates or simply tip of a wire. Use short wires to connect touch pads to the IC pins 1 and 6.

School Project 5. Movement Detector using PIR Motion Sensor. White LED turns on for few minutes when somebody move in front of it. Turns of automatically after the time out. IC CA3140 is used as a Comparator and its output becomes high when the positive voltage from PIR sensor reaches the Non Inverting Input Pin 3 of the IC. After the set time is over, output from the PIR Sensor stops and the Comparator turns off to switch off the LED. Ideal circuit to use near Stair Case, Wash Basin etc.

Note Pins of IC CA 3140 not shown in the circuit diagram. Connect like this

Pin 7 Vcc

Pin 4 Ground

Pin 2 Inverting Input. Connect the junction of 47 K and 10 K resistors to it

Pin 3 Connect the Cathode of 1N 4148 to this pin.

Pin 6 Output. Connect 470 Ohms resistor and LED to this pin

Use 4.5 volt to to 12 volt as power supply. 9 Volt battery is ideal. LED can be Transparent 5 mm White LED is 1 Watt White LED. 

School Project 4 Solar light turns on in the evening and turns off in the morning. Fully automatic. During day time, battery charges through Diode D2. Base of Transistor BD 140 becomes high through 4.7 K resistor and remains off. When the voltage from the Solar panel reduces in the evening, base of BD140 turns low and conducts. LED gets power from the battery and turn on.

Note Use 6 Volt 100 mA Solar panel. Transistor can be any Medium power PNP Transistor. Keep switch in the On position always and turns off only when the light is not needed to conserve battery.

School Project 3 Simple but efficient Fire Sensor. Beeps loudly when it detects Fire. Photodiode is used as the Flame Sensor. It receives IR rays from the flame and conducts. MOSFET Z44N triggers and Buzzer sounds.

Note Connect the Photodiode ( IR Receiver ) in the Reverse biased mode. Cathode to 1 Meg resistor and Anode to Gate of MOSFET. Keep Photodiode in a black tube to prevent triggering in ambient sunlight.

School Project 2 Simple Fire Alarm. Beeps loudly when it detects Fire. NTC Thermister 1K detects heat and conducts. Reset pin of IC NE 555 becomes high and IC triggers. Output from the IC activates BC547 Transistor . Buzzer beeps and LED lights. This continues till Fire ceases and the Thermister cools.

School Project 1 . Simple LDR controlled White LED light. Automatically turns on in the evening and turns off in the morning. Adjust VR1 to set the sensitivity of LDR to a particular light level. IC NE 555 is used as a Bistable

This Constant current Constant voltage charger module can be used to charge Lithium Ion batteries or other batteries. It is a 5 Amps 75 Watts Xl4015 DC DC converter and the the output voltage can be adjusted from 1.25 volts to 36 volts DC. It is not a Voltage Boost module but a Step down module. The output voltage can be below the input voltage given. If the input voltage is 12 volts, output can be 1.25 to 12 volts. If the input voltage is 38 volts, output can be adjusted between 1.25 volts to 36 volts.

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Battery maintenance is very important when we use Home inverters. Generally Tubular batteries are recommended due to its high efficiency and life span. Various makes and types are of batteries are available in the market. . Tubular batteries are recommended to backup UPS and Inverters where environmental conditions are tough and ambient temperatures are common. These are capable of long hours of backup and the life period is around five years.

Battery is the backbone of the inverter. Maintenance free batteries come in Flat plate collectors and are totally maintenance free. These batteries have a typical life of 4 years if properly charged and maintained.

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Test the continuity in wires, PCB tracks, Fuses Bulbs etc using this simple Continuity tester. Buzzer sounds and LED lights when there is continuity between the Probe’s contact points.

Protect the Home Locker with this simple Alarm. When somebody opens the Locker, it sounds an alarm till the locker is closed again.

Idea of the circuit is simple. When the circuit is placed inside a locked locker, darkness in its inside increases the resistance of LDR, So, Zener diode will not get its breakdown voltage and remains off. The buzzer driver Transistor BC 547 also will be off. When the door of locker opens, light enters and LDR gives current flow to charge the 100 uF capacitor, When its voltage increases above 5 volts, Zener conducts to switch on the transistor. Buzzer then sounds .

A natural doubt will arise. What will happen if the locker is opened in the night? Its answer is simple. User needs room light to use the locker. A Burglar uses a torch to search for valuables. In both cases, LDR gets light and alarm sounds. So it works day and night.

A single low power IC UM 3561 can make four different siren tones just changing its pin connections. Its pin 5 is Vcc and needs only 3 volts from two pen cells. Maximum Vcc should be 4.5 volts. It is a ROM IC with pre recoded tunes. The 220 K resistor between its pins 7 and 8 determines the frequency of tone. So do not change its value. Pin 2 is ground pin. Pin 3 gives feeble output which can be amplified by a single transistor that drives an 8 ohm speaker.

The diagram shown is an Ambulance siren by connecting its pin 6 to ground. By connecting pin 6 to Vcc pin 5, IC generates Fire engine sound. By keeping pin 6 not connected, IC gives Police siren. By connecting pin1 to Vcc pin 5, IC gives Machine gun sound.

A simple solution to confirm whether a battery is charging or not. You can add this to the Car battery charger.

It confirms 1. Battery is properly connected 2. Current is flowing from the charger to the battery.

When the circuit is connected to the charger, LED remains off. But when the battery is connected, LED turns on. At first, the LED brilliantly lit indicating that current is flowing to the battery. Once the battery is fully charged LED turns dim.

There is a resistor R2 ( R Sense ) between the Emitter and the base of the PNP transistor BC 557 . Its value is selected as 27 Ohms to drop 24 mA current .When a current higher than 24 mA passes through the R Sense resistor, LED brightness increases. Circuit gives around 100-150 mA current for slow charging. Use a transparent Red LED.

In many homes, Wireless Door bell is used. It has a Bell unit that gives around 24 types of tunes and a Bell switch unit placed outside the home on gate pillar or near the front door. We can convert this bell into a Motion sensing Door bell. So somebody move in front of the Bell switch , Door bell automatically turns on for few seconds and then turns off. Again triggers in another movement.

You need a PIR Motion Sensor Module, BD 139 transistor, two 1K resistors and one LED to modify the Door bell into Motion sensing Door bell. Power supply can be 12 DC.

Open the Bell switch unit and remove the 12 volt battery in it. Below the Press button, there are two contact points that make contact when the button is pressed. Short it. Connect 12 volt power supply. Tap 12 volt for the Bell switch unit from the Emitter of BD 139 transistor and ground. Connections over. Enclose the set up in a box with the Lens of PIR sensor and LED exposed from the box.

Switch on the Door bell and move in front of the Door bell switch Unit. Bell will sound. In the night, the tone of the Bell can be changed to Alarm mode. So it works like a Burglar alarm.

Two high power transistors in Darlington combination works as a Variable power supply. NPN Transistor MJE 13005 can handle 400 volts and 4 Amps current. Its power handling capacity is 75 watts. PNP Transistor MJE 2955 also has similar parameters. If the input voltage is 14 volts, output voltage can be adjusted from 1 V to 12 V by turning the 1K Pot.

TV Remote has an Infrared LED in its front. It emits invisible Infrared light that pulsate at 38 kHz. This tester has an Infrared Sensor Module that senses only the Infrared rays pulsating at 38 kHz. The IR sensor present in the TV senses the coded infrared pulses from the Remote and functions accordingly.

We can check the Remote using this tester whether it is working or not. Just focus the Remote on to the IR sensor of the tester and press any key. LED in the tester will flash and confirms the working of Remote.

Make your own Bluetooth speaker using the Bluetooth Module. When paired, it will wirelessly play music from your Mobile phone. It is powered by a Mobile charger. Stereo output from the Bluetooth Module goes to a 3 watt Stereo Amplifier Module. Two small 8 Ohm speakers are connected at the output of the Amplifier Module. Whole set up can be enclosed in a small box. You can use two small computer speaker boxes for that.

Power the circuit, and see the Bluetooth connection in the Mobile phone. The Icon of Bluetooth Module will appear in the Mobile phone. If not, scan the nearby devices. Once detected, you can pair the Bluetooth Module with your phone and play music.

Tiny Emergency light that turns on when power fails. A handy match box sized emergency light useful during travel. 4 Volt battery in it charges via a Mobile charger. Red LED indicates that the battery is charging and mains power is available. During that time, PNP transistor BC 557 remains off due to the positive bias in its base through 4.7 K resistor. White LEDs remains off. When power fails, base of BC557 turns negative and it switches on to light the White LEDs. Keep switch S1 in On position to work it as Emergency light and keep it in Off position when the light is not needed. Battery can be a small 4 volt rechargeable battery.

This LED Flasher gives brilliant flashes. It is not a conventional transistor design and looks absurd. But still it works properly. I am using this flasher continuously as a Mock flasher for the last two years. Still its performance is excellent.

Transistor BC 547 is using as a reverse biased diode without connecting its base to anywhere. Charge and discharge of 470 uF capacitor determines its flash rate. With this value, it is one flash in one second. Use a 5 mm Red coloured transparent LED. Circuit works only above 11. 5 volts.

It can be an ideal indicator for 12 volt battery chargers. When the battery attains 12 volt, LED starts flashing. When the battery full voltage reaches 13.8 volts , Flash rate increases. Try it and see the result. Remember; use only 12 volt power supply. It will not work in 9 volt battery.

This simple circuit beeps loudly when the water tank start to over flow. So no more wastage of water. N Channel MOSFET IRF Z44 N is used as a switch. Buzzer and LED are connected in series with 100 Ohms resistor to the Drain (D) of the MOSFET. Source (S) of MOSFET is connected to ground. Gate (G) is connected to the Source through 1 M resistor to prevent latching of MOSFET so that buzzer will turns off when the water level drops.

Fix the probes (with 1 cm gap) just below the rim of water tank. Power and switch on. When the water level touches the probes, buzzer sounds and LED turns on. When the water level drops, probes loose continuity and buzzer stops beeping. 9 Volt battery or 12 volt adapter can be used as power supply.

Simple but efficient LED light for Garden. Turns on in the evening and turns off in the morning. 6 Volt Solar panel charges the battery in sunlight. 4 volt battery power the LED in night. During day time, PNP Transistor BD140 remains off due to the positive state of its base through 4.7 K resistor. When the current from the solar panel decreases in the evening, base of BD140 will be pulled to ground via 1 M resistor and the transistor turns on to light the 1 watt White LED. In the morning, the condition reverses and the LED turns off.

A Warning lamp for places where machineries are operating. It flashes continuously to remind that there is high voltage and heavy machinery is running. It can also be used as a warning lamp in roads where road work is progressing.

Lamp flashes due to the charge and discharge of 470 uF capacitor and the switching of Diac DB3. When the capacitor charges fully, Diac DB3 fires and Triac BT136 conducts. This turns on the Lamp. When the capacitor discharges, Diac turns off to switch off the Triac. This turns off the lamp. This cycle repeats and the lamp flashes continuously. By lowering the value of capacitor, the flash rate can be increased. Flash rate can be slowed down by increasing the value of the capacitor.

Caution: AC Circuit that can give fatal shock when handled carelessly. Do not test or troubleshoot when the circuit is connected to mains.

Most simple Fire Alarm using a Photodiode as Flame sensor. When the Infrared light from the flame falls on the reverse biased Photodiode, it conducts and switch on the transistor BC 547. Buzzer beeps and Red LED lights to indicate Fire.

White LED turns on in the dark and turns off in the light. When there is light, LDR offers less resistance and conducts. Transistor BC547 will not get sufficient base bias and remains off. White LED connected to its collector also remains off. In dark, resistance of LDR increases and transistor gets base bias and conducts. LED then turns on.

It turns on in the evening and turns off in the morning. Triac BT 136 is used as a switch to control the lamp. LDR senses light intensity. When the LDR conducts during day time ,  Diac DB3 will not get sufficient threshold voltage ( 34 V ) to fire. So Triac BT136 remains off. Lamp also will be off. When the resistance of LDR increases in the night, it conducts less and Diac fires to switch on the Triac. Lamp turns on.

Triac BT 136 can handle up to 250 watts load with a heat sink. Use ordinary bulb or LED bulb.

Caution : AC Circuit that can give fatal shock when handled carelessly. Do not test or troubleshoot when the circuit is connected to mains.

Here is a Simple Flashing LED indicator for the switch boards. One end of it can be connected to the point of switch going to the load and the other end to the neutral. When the switch is on, LED starts flashing. So it confirms that the load is switched on. This is useful to monitor the working of battery chargers and other devices that are continuously switched on. Alternately, it can remind to switch off high current devices like water heater, electric iron etc after the use.

Working of the circuit is simple. 47 K, 1 watt resistor drops 220 volt AC and 1N 4007 diode rectifies it. 47 uF capacitor charges slowly. When the voltage in the capacitor increases above the threshold voltage ( around 34 volts ) of Diac DB3, it conducts and capacitor discharges. This lights the LED. When the capacitor discharges, LED turns off. This cycle repeats and LED turns on /off alternately .

Simple Variable supply using Variable voltage regulator IC LM317. If the input voltage is 32 volts, output voltage can be adjusted from 1.2 volts to 28 volts by turning 10K Pot. Use a Heat sink for LM317 to dissipate heat.

Minimum Input voltage 4.2V

Maximum output voltage 40V

Minimum Adjustable voltage 1.2V

Maximum adjustable voltage 37V

Maximum output current 1.5A

Simple 3.7 volt Lithium Ion battery level indicator. Green LED lights when the battery is full with 3.7 to 4.2 volts. When the battery voltage decreases below 3 volts, Green LED turns off and Red LED lights. Just connect it to the 3.7 volt battery charger.

No need of a circuit diagram.Connect 1N 4007 diode, a White LED and 33K 1 watt resistor in series with Phase and Neutral of 220 V AC. It is similar to commercial type night lamp. You can fix it in the switch board itself. But need caution since it is directly connected to AC.

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1 Watt LEDs are widely used in Emergency lights and LED lights. Most of the circuits use 4 volt battery having 0.5 to 4 Ah capacity. The 1 watt LED is rated 3.6 volts so we need the correct value resistor for LED to get maximum brightness. Let us see how the LED resistor value is determined.

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The DC DC Booster 150 watts Module can be used convert 12 Volt DC to 35 Volt DC for various applications. It can be an ideal DC DC Booster to charge Laptop and Note book using 12 volt Car DC charger socket. It can also be used to increase the Solar output voltage in low light conditions. It gives maximum 6 Amps current .

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It gives a short beep when mains power fails. Uses only three high value capacitors, buzzer,two LEDs and a 12 volt DC power supply.

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A Compact design of PIR Motion Sensor light using Transformerless power supply and Triac for switching. Everything can be enclosed in a small case. Light turns on when it senses human movement and remains on for three minutes and turns off. Retriggers in another movement. Detection range is 10 meters maximum.

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Digital Volt Ampere meters are now available to measure DC voltage and Current. It can be connected to the output of the Power supply. So the output voltage and current to the load are displayed in the meter. If a battery is connected to the power supply for charging, we can see the current consumed by the battery during charging. When the battery is fully charged, current drops to zero which indicates termination of charging. If the project is connected, the voltage and current consumed by the project are displayed in the meter.

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Here is an efficient Car battery charger for fast charging the Car battery. It is a 5 Ampere charger with Digital Volt and Ampere Meter to display the charging voltage and current. Since the charger provides maximum 5 Amps current, battery can take high current it needs to charge very fast. As the charging process completes, current flow reduces to zero and will be displayed in the meter. So it is easy to confirm whether the battery is fully charged or not.

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This simple circuit can indicate the condition of Phase, Neutral and Earth wiring in the domestic power supply. If Phase, Neutral and Earth lines are intact, Red, Yellow and Green LEDs glow. If Earth line is brocken, Green LED remains off. If either Phase or Neutral line is brocken, all LEDs remains off. The circuit can be enclosed in a Three pin plug. Just plug it in the socket and check the conditions of home wiring.

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Just move hand in front of this Liquid soap dispenser. You get few drops of liquid soap for hand wash. Made it Non contact to prevent hand contamination from the press handle of the dispenser if it is used in common places.

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A Simple Water level indicator circuit indicating 5 stage water levels in the tank. LED1 glows when the water tank is empty. LED 5 glows when the tank is full. LED 2 indicated 40%, LED 3 indicates 60% and LED 4 indicates 80% water in the tank. LEDs glows one by one when the water tank fills and turns off one by one when the water level drops.

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Very sensitive. Detects Fire from a distance of 2 meters in a dark room. Beeps loudly till Fire ceases. Since it is detecting Infrared rays, it can be also used as a TV Remote tester.

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Save water .This simple circuit beeps loudly when the water tank becomes full.No more wastage of water.

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Turns on a White LED for 3 minutes and turns off when a human move in front of it. Uses Passive Infra Red (PIR) motion sensor.

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The Op Amp comparators sometimes works well under some conditions but not always. If there is a slow wave form or some noise on it, sometimes the output switch back and forth many times. So for stable operation, Op Amp comparator can be designed as a Schmitt trigger.

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Comparator is a circuit that compare two voltages. When one voltage is higher than the other, the output of comparator is in one state, either high or low. If the input conditions are reversed, output of the comparator switches to the other state.

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Two LEDs indicate the power on and off status of bread board power . So it helps to confirm whether the positive and negative rails of the bread board are getting power. Green LED lights at power on and turns off after 3 seconds. Red LED turns on at power off and turns off after 3 seconds. Let us see the circuit

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It is easy to light an LED by directly connected to 220 volt AC. It can be indicator in AC devices or Bed lamp if White LED is used. If used as a Bed lamp, the circuit can be enclosed in a plug  with LED projecting out.

Caution : The circuit is directly connected to high voltage that can give a fatal shock if handled carelessly . Do not test or troubleshoot when connected to mains. 

This circuit can protect AC appliances. When the AC voltage in the mains increases above the set level , say 220 volts, relay triggers and breaks power from the appliance. Reconnects the appliance when the power returns normal.

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Beep once when power fails. 12 volt relay is used as a switch. When power is available, relay pulls and capacitor charges via diode D1 and NO and Common contacts of relay. When power fails, relay turns off and capacitor discharges via Common and NC contacts and buzzer. Buzzer gives a short beep at that time. If more timing for beep is needed, connect one more 4700 capacitor parallel to C1. 12 Volt DC for the circuit should be from a 12 Volt adapter or transformer power supply.

The Project implementing is a Gas leakage alarm system that senses the leakage of LPG from Gas cylinder or Gas stove and gives a warning alarm. Its further modification can be automatic cut off the electricity system in the home and also a battery operated exhaust fan to remove the leaked gas from the room.

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Battery maintenance is very important when we use Home inverters. Generally Tubular batteries are recommended due to its high efficiency and life span. Various makes and types are of batteries are available in the market. . Tubular batteries are recommended to backup UPS and Inverters where environmental conditions are tough and ambient temperatures are common. These are capable of long hours of backup and the life period is around five years.

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