You can use this Flashing LED light for Projects, Model vehicles, Toys etc. It blinks in a peculiar fashion with bursting flashes.

The circuit uses IC CD4060 which is Binary counter with 10 outputs. Each output goes high one by one in a binary fashion. That means, second output remains high with double time than the first one and so on. The IC oscillates with the capacitor connected to its pin 9 and the resistor (VR1) to its pin 10. The oscillations are fed to the input pin 11 through the 1 Meg resistor. Out of the 10 outputs, only two outputs (Pin 6 and 7) are used to drive two NPN transistors.LED is connected to the collector of T1 through the 100 Ohms current limiting resistor. T1 and T2 are wired as amplifiers. Reset pin 12 of IC is grounded via resistor R1.

So at power on, IC oscillates and first output turns high after few seconds and triggers T1. After few seconds, second output turns on and T2 conducts. The synchronous actions of T1 and T2 give the Strobe light effect from the LED.

This circuit tells you how much radiation is coming from electric devices. It picks up the AC hum from the surroundings of electric equipment and electric wiring and blinks the LED to show the radiation level. You can also use this to assess the safe distance from Computer radiation.

Circuit uses a Piezo element to collect the radiating energy from the electric equipment. Piezo element is commonly used in Piezo buzzers to generate sound. It is a circular metal plate with a coating of Piezo electric material. It can accept and store energy from the electric field.

IC CD 4017 is the Johnson Decade Counter commonly used in chaser circuits. Its input pin 14 is very sensitive to external pulses. The electromagnetic pulses captured by  the Piezo element enter into the input of IC and its outputs turn high one by one. Here only one output (pin3) is used to drive an LED. Output pin 4 is connected to the reset pin 15 to prevent further counting.

When the Piezo element is around 1 foot away from the electric wire or equipment, LED starts blinking. Press SW1  while testing.

Mosquito Repelling vaporizers are generally switched on throughout night to repel mosquitoes. This is not necessary because Mosquitoes become active during the evening hours for feeding. If it enters the home in the evening, it will bite in the night also if gets a chance. So the best method is to use the vaporizer in the evening hours. This circuit automatically turns on the vaporizer around 6 pm and keeps it on till 9 pm and after that, it switches of the vaporizer. This reduces the quantity of inhaling fumes and also increases the usage days of vaporizer. The circuit can be enclosed in the switch box itself.

Transformerless power supply is used to power the circuit which gives around 15 volt DC. Capacitor C1 drops 230 volt AC to low volt AC which is rectified by the Full wave bridge rectifier module and made ripple free by the smoothing capacitor C2. Resistor R1 bleeds the stored current from C1 at power off and the resistor R2 protects the circuit from inrush current at power on. Green LED indicates the power on status.
The circuit consists of a Timer section and a relay for connecting the vaporizer to mains. Timer is built around the popular Binary counter IC CD 4060 (IC1). It is activated in the evening by using an LDR in its reset pin 12. CD 4060 is the Binary counter IC with 10 outputs which turns high one by one in a binary fashion when it oscillates using the capacitor (C3) connected to its pin9 and the resistor (R5) in its pin 10. The internal oscillations of the IC are fed to its input pin 11, so the outputs go high one by one based on the frequency of oscillation.

During daytime, IC 1 remains standby since its reset pin is high due to the conduction of LDR. When the room light reduces in the evening, LDR reduces its current flow and the reset pin of IC1 turns low. This activates the IC and it starts oscillating. Yellow LED connected in its first output (Q4) starts blinking at the rate of one in 9 seconds. After one hour and thirty minutes, Q13 of IC (Pin 2) turns high and activates the relay driver transistor T1. Relay then turns on to connect the Vaporizer to the mains through its common and NO contacts. Red LED indicates the activation of the relay. Capacitor C4 gives a short lag for the switching of T1 which eliminates unwanted relay clicking. Diode D2 removes back e.m.f and protects T1 when the relay turns off. Pot VR1 can be used to adjust the sensitivity of LDR at the particular light level in the room around 5 p.m.

Vaporizer remains on for around three hours to repel the mosquitoes. When the Q14 output (Pin 3) of IC turns high after 3 hours, relay turns off. At the same time, diode D1 forward biases and inhibits further oscillations of IC. So IC will not advances further and the Q14 output remain high till IC resets in the morning when the LDR gets light. So no need for switching the vaporizer every day and it automatically performs its duty. If there is a need for switching the vaporizer again in the night, use the manual switch S1.

Assemble the circuit on a common PCB as compact as possible to enclose inside the switch box. Give sufficient space between the power supply section and the circuit. Power supply section should be carefully assembled to avoid shorting the components. Since 230 volt AC is present in the power supply section, shorting can cause fire. It is better to construct the power supply section on a separate PCB. Enclose it in a plastic case to prevent shock hazards. Connect the relay contacts to the three pin plug as shown in the figure. Place LDR on the Switch box to get ambient day light. Light from the fluorescent lamps should not fall on LDR.

Note – 474 – 400 V ( 0.47 uF )capacitor can deliver sufficient voltage for the circuit. In places where there is voltage drop in mains, it is better to use either 105K 400 V or 225K 400 V capacitor instead of 474. 

Caution: This circuit is extremely dangerous if handled carelessly since it carries high volt AC. So do not touch or troubleshoot when connected to mains.

CD 4060 Binary counter

It has 10 outputs that delivers 4.6 V at 5
V Vcc , 8.6 at 9 V Vcc and 11.6 V at 12 V Vcc so to limit voltage and current, a resistor is needed in its output. See the basic design of CD 4060 given in the website talkingelectronics

Potentionmeters are manually adjustable variable resistors with three terminals. Two terminals are connected to the ends of the resistive element, while the third terminal is connected to a sliding contact called Wiper.So by rotating the wiper, the resistance of the Potentiometer can be adjusted to its maximum value. The position of the wiper determines the output voltage of the Potentiometer.Potentiometer is commonly called as “Pot meter” or simply “Pot”. “Log ( Logarithmic ) Pots” are used as volume control and “Lin ( Linear ) Pots” are used for other applications.Different materials are used as resistive material in Pots. This may be Carbon, Cermet, Wire wound, Conductive plastic or metal film. Usually, the value of the Pot is printed on its body. But the miniature “Trimpots” have codes to represent its value. For example, 102 (1K), 103 (10K), 104 (100K), 105 (1M) etc. Checkout the different types of Potentiometers.

PIR Sensor Module is one of the new introductions in electronics which is a highly useful device to switch on lights when it detects a human movement. It turns on the lights from 30 seconds to 3 minutes depending on the preset adjustments. Its range can be as high as ten meters which can also be adjusted. The module gives a high output when it detects the human movement. This high output can be used to drive a relay through a switching transistor. Let us see the details of PIR sensor module.

How it works?
All warm blooded animals especially human beings emit Passive Infrared ( PIR) from the body heat. The sensor module has a PIR sensor. Inside the PIR sensor, there are two Pyroelectric sensors. One is Reference sensor and the other is Trigger sensor. The Reference sensor remains active by considering the background temperature as reference. When a human movement occurs, it causes minute changes in the atmospheric temperature due to PIR from human body. This change is sensed by the trigger sensor and a corresponding output voltage appears.

The PIR sensor Module has PIR sensor, Signal amplifier circuit and a Timer circuit. The weak output signal from the PIR sensor is amplified by the signal amplifier and triggers the timer circuit. So the output from the module turns high based on the setting of the delay preset.

How to connect?
PIR Sensor module has three pins for connections. Vcc pin, Ground and Output. So a three pin connector can be used to connect the module with the relay driver circuit.

Power requirement
PIR sensor has power regulation and it works between 5 volts and 12 volts. Output gives 3.3 volts which is sufficient to drive the switching transistor. Use a Transformer based power supply or battery to avoid false triggering.
Settings
There are three adjustments in PIR sensor module

Delay – It is a miniature trim pot to set the time delay of output from 30 seconds to 3 minutes. Turn the preset clock wise to increase the time delay.
Sensitivity – The preset can be turned clock wise to increase sensitivity from 30 c.m to 10 meters.
Trigger – There is a Jumper arrangement to select single trigger of multiple trigger. In single trigger mode, the sensor triggers with a single movement. In multiple trigger mode, the sensor turns active only when there is multiple movements.

Night active setting.
There is a provision for adding an LDR in the module so it becomes active only after sunset.
Initial setting
The PIR sensor module should be fitted 2-3 meters above the ground level at an angle of 45 degree because its sensing area is in a cone of 45 degree angle. It should be fixed in an area free from direct sunlight, moisture etc. There should be a background like wall to get more accuracy of sensing. Initially at power on, the sensor triggers and switch on lights. After the set period, output goes low and light turns off. Now the sensor is idle to sense further triggering. It takes around 10 minutes for stabilizing the sensor.

False Triggering – Sometimes the Sensor shows false triggering. Shadow of trees, sudden changes in sunlight, power fluctuations, Fluorescent lamps, Fly, animals like Cats, Dogs etc can cause false triggering. If a light is used with the relay, it will not cause nuisance and if alarm is connected, it may create some nuisance. 
Cost
The PIR sensor is mainly imported from China and Taiwan etc. Now it is a low cost one and its rate will be between Rs. 70 and Rs.200 based on the quality.

LPG Sensor modules are available now at low cost and we can use it in the Kitchen as a Gas leakage Alarm. The Module has a MQ6 Gas sensor, an Op-Amp as comparator and a preset for adjusting the sensitivity. All we need is a load resistor at the output to connect with the alarm circuit. Module is very sensitive to LPG (Liquefied Petroleum Gas) which contains Propane and Butane. The MQ6 sensor detects the gas concentration between 200 to 10,000 ppm.

The module works off 5 volts DC and has two outputs.
1. The Analogue output ( A) can be used to drive a buzzer through a driver transistor.
2. The Digital output ( D) can be used for Micro controller based circuits.
The MQ6 LPG Sensor has 6 pins. But in the Sensor module, the MQ6 is already connected.

This is how the Gas sensor module is used to drive a buzzer as alarm

How to Test?
Connect the Module with the Buzzer driver circuit . Adjust the Preset in the module just to turn off the output LED. Then light a Cigarette lighter and keeping its knob pressed, puff off the fire. You can smell the gas. Show it near the Gas sensor and adjust VR1 (Load resistor) till the buzzer beeps. Place the circuit on the wall 1 foot above the Gas cylinder. Use a 9 volt battery to avoid electric wiring.
More about gas sensors
Gas Sensors are devices which detects the presence of gases in an area. These are used for safety purposes to activate alarm systems as warning measure or to shut down a machinery. Gas detectors are used to detect different kinds of gases like combustible, flammable and toxic gases.

Catalytic detector
Catalytic detectors use the basic oxidation principle to detect a combustible gas like LPG. When the gas oxidizes, heat generates and the gas sensor converts this heat in to corresponding electric signals. A standard Wheat stone arrangement is used for this. The output from the gas sensor is equal to the concentration of gas in the area. The heater inside the sensor has two heating elements. One is the active element and the other is the reference element.


The active element is placed in the catalyst. When the combustible gas reacts exothermically with the oxygen, temperature rises due to catalytic action. The rise in temperature changes the resistance of the active element. The catalytic reaction takes place on the surface of the catalyst. The reference element is non- responsive to gas and gives the base line signal to compensate atmospheric temperature changes. This prevents false triggering of the alarm system.

6 Pin Gas sensors
These are sensitive semiconductor Gas sensors that give an analog voltage at the output when the air contains Combustible gas molecules. In clean air, it gives low voltage and when the gas concentration increases, output voltage also increases accordingly.
The Sensors are provided with 6 pins but 4 pins are sufficient for connection.

H-H pins – These are used for providing 5V DC to the heater element. These pins have no polarity and one H can be connected to 5V DC and the other to the ground.
Pins A – A (or B-B). The A and B pins can be used for providing 5 V DC or to get output voltage. If the pins A are used (by shorting), pins B( by shorting) act as the output or Vice versa.

An Ultra sensitive Vibration Sensor SW 18020 P is now available from the Gaoxin. It can be used in different ways to sense mechanical vibrations to activate alarms and other surveillance systems and a variety of vibration detection projects.
The Vibration sensor has two electrical contacts which are not connected in idle condition. When an external force is applied due to movement or vibration , the Sensor’s contacts close. When the force is removed, the sensor terminal returns back to open contacts. The internal spring closes the contacts during vibration which triggers the circuit connected to it.

How it works?
The sensor is made up of a small spring mechanism, which makes the contacts ON when a vibration force is applied above a certain threshold level. Two pins coming out of the sensor  are insulated by a resistance of more than 10 M Ohm. When a Vibration force is applied on the switch, the spring inside the switch vibrates and makes a momentary short circuit between the two terminals. The terminals of the Vibration sensor has no polarity but one pin is thick. Use it to connect to Vcc through a resistor and connect the thin pin to the circuit to be triggered.

How to Test?
Before using the Vibration sensor in Projects, test whether it is working properly or not. A simple LED circuit shown below can be used to test the Vibration sensor. Use the Sensor as a Switch for the LED circuit. After powering, gently tap on the sensor. LED will light momentarily and turns off. When the Sensor gets vibrations, its contacts close and gives current to LED and it glows. When the vibration ceases, contacts break and cut of power to LED.

Specification
1. Maximum supply voltage is 12 V DC but it works from 3-12 V DC.
2. Maximum current – Less than 5 Ma
3. Open circuit resistance – Higher than 10 Mega Ohms
4. On resistance – Less than 5 Ohms
5. Life expectancy – More than 5 Lakh times
6. Response time – 2 ms
Applications
The Vibration Sensor can be used in applications like Anti-theft alarm, Smart Home Systems, Automotive devices, Home electrical devices. Air condition blower fall prevention protect switches, Communication devices, Electronic scale, Meters, Robots, Toys etc.

TP 4056 is a Constant voltage – Constant current Chip used for charging a single 3.6 V Lithium Ion battery from 5 volt power source including USB port. It sources constant 4.6 volts for charging. An external Programming resistor can be used to provide constant current for charging. The Chip can handle up to 1 Ampere current. It has internal protection circuitry for polarity reversal, so external diode is not necessary.

The chip senses both charging and full charge status of the battery and two LEDs can be used for visual indication. Red LED lights during charging and Green LED lights when the battery is fully charged. R Prog is the resistor that controls the charging current . An NTC Thermister can be added in series with the R Prog resistor to control current based on temperature. In the circuit, a 10 Ohm NTC Thermister  is added in series with the R Prog resistor( 47 Ohm ). The Chip provides 4.6 V constant voltage for charging. So in the cold condition, total resistance of NTC and R Prog will be 57 Ohm . So current will be 80 mA ( 4.6 / 57 = 80.70 mA ). NTC should be fixed close to the battery.

LM 1117 is the tiny Fixed Voltage Regulator that drops 5 Volt DC to fixed 3.3 V DC. It can output maximum 800 mA. Like 78XX series Voltage regulators, LM1117 is also a three pin device with In, Out and Ground pins. Ideal Voltage regulator for Microcontroller and Arduino Projects that needs fixed 3.3 volts.

Only two capacitors are needed with LM 1117 to make a low voltage regulator power supply. Input can be 5 Volt DC up to 1 Amps which can be derived from the USB port also.

MOC 3041 is the Optoisolated Triac Driver that can be  used to isolate AC portion of the circuit from DC operated circuit board. It helps to prevents the damage of DC circuit when there is an accidental leakage of AC in Triac controlled lamp driver circuits.

MOC 3041 has built in Zero Crossing Sensing ( ZCS) for On / Off applications. The chip has an LED and an optically active SCR in a common package. The LED is driven by the DC output voltage from the circuit while the Optically active SCR carries 230 volt AC. The SCR drops the 230 V AC to low volt AC and rectifies it into DC for driving the gate of external Triac. When the output from the DC circuit comes, the LED inside the MOC turns on. This triggers the SCR and MOC gives DC output to drive the Triac.

MOC 3041 has 6 pins and pin 1 is the Anode of LED and pin 2 is its Cathode. Pin 6 receives 230V AC while pin 4 gives output voltage to drive the Triac.

The circuit given below is a Lamp Dimmer with MOC isolation. The DC circuit board has a variable output either controlled by a Variable resistor or Microcontroller. Depending on the output voltage from the DC board, the LED inside the MOC varies in brightness. As a result, the voltage from the SCR varies to provide a varying voltage to the gate of external Triac. The lamp connected between the M2 pin of Triac and the Neutral line  shows the varying brightness accordingly. If a steady output voltage is given to MOC, it acts like an On/ Off switch for the lamp.

Caution : The circuit carries high voltage and gives Fatal Shock if handled carelessly. Do not attempt to build this circuit unless you are competent to handle high volt circuits. Do not touch the MOC and the circuit when connected to Mains.

TCRT 5000 is a highly sensitive IR reflective Sensor that has an IR lED and a Phototransistor in a common package. It is an ideal module for projects like Robotics, Position sensing, Detection of Reflective materials etc. Its range is 2-10 mm and best response range is 3 mm.

The Infrared Sensor has two parts. An Emitter and a Receiver. Emitter is the IR LED that has Anode and Cathode pins. A Current limiting resistor of 470 Ohms to 1K should be added in series with the Cathode of IR LED. Anode of IR LED should go directly to Vcc. The receiver is a Phototransistor with Collector and Emitter.A load resistor of 10K should be added to the emitter of Phototransistor and its Collector should go directly to the Vcc.

The Reflective sensor gives two types of outputs based on the intensity of the Reflecting IR rays falling on the Phototransistor. The Analogue out put is in terms of DC Voltage. That means, when the Phototransistor is not receiving the reflected IR rays, output is 0V and when the Phototransistor gets reflected IR rays, output voltage increases from 0V to around 3 V based on the intensity of the reflected light. The Reflective Sensor also has Digital output. That means, when the Phototransistor is not getting reflected IR rays, output remains in Logic 0 and when it gets reflected light, output turns to Logic 1.

A Test Circuit is give below. An LED is connected to the output of the Reflective sensor for visual indication. When there is no reflective surface in front of the sensor, LED remains off indicating Zero output ( Logic 0 ). When a reflective surface such as white paper is present in front of the sensor (around 2-5 mm distance ), LED turns on indicating High output ( Logic 1 )

DS 18B20 is a Programmable Digital Temperature sensor that gives Digital outputs based on the temperature. It provides 9-12 configurable Bit temperature readings which indicate the temperature of the device. Information is sent to / from to connect from a Central Microprocessor to the DS 18B20. Power for reading, writing and temperature conversion can be derived from the Data line itself so that no external power source is needed.

DS 18B20 contains a unique serial number, multiple DS 18B20 s can exist on the same 1 – Wire bus.This helps to connect many temperature sensors in different places. It can be powered from the data line itself. Power supply range is 3.0V to 5.5 V. It measures temperatures from -55 Degree C to + 125 Degree C. It converts 12- bit temperature to Digital word in 750 ( Max ).

Applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system etc.

Bridge Rectifier is used to convert AC to DC and the process is known as Rectification. IN 4007 diodes are used to make a Fullwave Rectifier bridge. After rectification, the AC ripples from the DC will be removed using a high value Smoothing capacitor. Bridge Rectifier modules are available to make the circuit compact. DB107S is the SMD version of the Bridge rectifier Module. It is some what larger in size, so that it can be soldered easily. DB107S can handle up to 1000 volts and 1 Ampere current.

DB107S has four pins. Two pins are used to connect with the low volt AC from the Transformer while the other pins ( + and – ) are used to tap DC voltage.

P6KE12A is a very good TVS (Transient Voltage Suppressor ) Diode that can be fixed across the power supply lines to block the transients. It is rated 600 Watts and protects the sensitive electronic devices from the voltage spikes induced on circuit. It can handle up to 12 Amps current. Ideal device to attach across, Telephone lines, Cable TV lines, Transformer power supply etc. It works like a simple Lightning Arrester.

TVS Diode operates by shunting excess current when the induced voltage exceeds the Avalanche breakdown potential of the Diode. It works like a Clamping device, suppressing all over voltage above its rated breakdown voltage. When the transients is over, the diode reset back to its normal position.
Connect like this

Accelerometer is an Electromechanical device that measures the acceleration process. The forces may be Static or Dynamic. Accelerometer Chip is now available to interface with the Micro controller based projects like Robotics, Drones etc. It is a tiny chip that senses the tilt and with reference to the G-force ( Gravity) it generates a tiny output voltage. A Comparator will measure the voltage and accordingly the micro controller sends signals for the corresponding movement.

A very good example of the working of Accelerometer is the movement of Touch screen in Smart phones.

The Smartphone senses its location, wobbling between horizontal and vertical screens, dancing Icons and so many parallax effects produced are due to the Accelerometer chip . The Accelerometer chip present inside the Smart phone measures the rate of tilt. It is basically available in 2 axis or 3 axis mode. The axis is represented as X-Y-Z just like a 3D figure. Whenever you tilt your phone, the Accelerometer senses that tilt and gives a corresponding output voltage. Using a Comparator, the voltage is measured based on the tilt. So it converts the physical movement to electrical energy. Based on the electrical energy levels, the Microcontroller senses the direction of tilt. The screen then goes to the opposite side of tilt. Side wise wiping of the screen is also the trick of the accelerometer.

Accelerometer Modules are now available which works off 3-5 volts DC. There are output points like X, Y and Z to interface with the Microcontroller. The Microcontroller directs the mechanical parts of the Robot to move according to the tilt sensed by the accelerometer.

Now a day’s many LED Torches and Emergency lights are using in Home which are powered by 3.6 Volt rechargeable battery. Due to improper charging, battery will damage and the torch becomes useless. In many of the makes, a Transformerless power supply is used to charge the battery but it may easily fail due to voltage spikes in the mains line. So here is a simple battery charger for all kinds gadgets using 3.6 V battery.

A 4.5 Volt 500 mA transformer is the main part of the charger. It is commonly used in Radio and Cordless phone adapters. Two Diodes (D1 and D2) rectifies the low volt AC to DC and the Smoothing capacitor C1 filters the ripples. Output from the rectifier – capacitor junction will have around 500 mA current which is too much for charging. Since slow charging with low current is a good method, a current limiting resistor R2 is added. Output will be 4.5 volts at 115 mA current. You can change the value of R2 for different current. Use Ohms law to select the resistor value.

V / R x 1000 = Current in mA.

Here 39 Ohms resistor is used as current limiter. So

4.5 / 39 x 1000 = 115.38 Milli Ampere

Make this external charger by enclosing the circuit in an adapter case. Connect a suitable pin for the socket provided in the Gadget for external charging.

If you own a Car, you need a Battery charger to charge the battery if the vehicle is not running daily. Car battery is rated 12 Volt 32 Amps or 45 Amps. It needs both charge and discharge cycles to keep the battery always in top condition. Aging of battery starts just after its manufacturing and as the age increases, the Lead Acid battery loses its capacity to hold charge. Here is a simple Car battery charger you can make.

What you need
1. A 14-0-14 Volt 5 Ampere Transformer
2. Two 10 Amps diodes
3. One 100 uF 40 Volts Electrolytic Capacitor
4. One 0-10 Amps Ampere Meter
5. Two Battery clips
6. A Metal box for enclosing the charger.
7. 2 Meters 1 mm Red and Black electrical wire

Here the charger uses 14-0-14 V 5 Amps Transformer. Battery needs more than 2 volts higher than its rated capacity for steady charging. If we use 12 volt transformer, output voltage may reduce below 12 V if there is voltage drop in the Mains. This causes improper charging. If the battery is aged, it needs a force charging initially. So 5 Amps transformer is selected. Transformer gives low volt AC between 14 V to 16 V which is rectified into DC by the 10 Amps diodes D1 and D2. Usually a large value Capacitor is used to filter AC ripples from DC. But here a low value capacitor ( C1) is used since some ripples in the DC is good for Lead Acid battery charging. A kind of pulse charging takes place when  the ripples  present in DC. You can also avoid that filtering capacitor.

Connect the Ampere meter in series with the Positive. From the Meter connect the Red wire with the Battery clip at the end. Similarly connect Black wire to the Negative side. Double check the polarity before connecting to the battery. No LED indication is provided since it may drop some output voltage. Meter gives good indication for charging. Its needle rises to 2-3 Amps initially and when the battery charging completes, needle returns to zero.

PIR Motion Sensor Modules are now available at low cost and it can be used to make Motion sensor alarms, PIR light switches etc. It requires only a few components and within few minutes, you can make a highly useful gadget for your home. Let us see the details of PIR Module and the circuits.

PIR sensor is an electronic sensor module that measures infrared light radiating from the objects including human beings in its field of view. It is generally called as Motion or Proximity Sensor, Pyroelectric Sensor etc. The sensor in the module detects the infrared radiation emitted from the human body in the form of body heat. Each object with a temperature above absolute Zero (273.15 Degree Celsius or 0 Kelvin) will radiate infrared rays.

PIR Sensor is called as “Passive Infra Red (PIR) sensor because it is not emitting any infrared ray but sensing the Infrared rays passively. PIR has two Pyroelectric sensors inside for comparing the infrared of the surroundings and the infrared rays from the human body. If the difference is too high, it triggers the circuit.
What is inside the PIR Sensor Module?
The PIR module is a fully assembled board with a current sourcing output which can be used to trigger a circuit.

1. Fresnel lens – The PIR sensor is covered externally by a dome shaped plastic cover which acts as a Fresnel lens to concentrate the Infrared to the sensor. It is built of tiny lenses that collect IR from different angles.
2. PIR Sensor – Inside the Fresnel lens cover, there is PIR sensor soldered in the module. It is the chief part of the module to receive the IR.
3. Connector pins – PIR Sensor module has three pins. Vcc that receives 3-12 V DC, Ground and the output pin. PIR sensor module very well works in 3 Volt DC but it handles up to 12 volt DC.

4. Potentiometers – Two Presets are provided to adjust the Sensitivity ( Range ) and the Time delay of the Sensor. The Sensitivity ( Sx ) can be adjusted to few cms to 10 meters. But good sensitivity is available in the midpoint of the preset. Time delay preset (Tx) adjusts the time period by which the output remains high. The Module has a timer circuit so that the output On time can be adjusted between 30 seconds to 3 minutes by turning the pot. When we place the Module down, the Preset close to the IC is Sx and the right one is Tx.

5. Re trigger Jumper – PIR Module has a Jumper to select two modes of operation. The Default setting may be in the “H” position. In the H position, the PIR sensor triggers only when a movement is sensed. In the Non retriggering mode, the Jumper is placed in the “L” position. In this mode, repeated triggering occurs when it detects movements. The “L” positing seems little erratic and output turns high and low repeatedly. So use the “H” position for stable operation of the circuit connected to the Module.

How to Test?
Before using the PIR module, first check its working and adjusts time delay and sensitivity according to your needs. Just connect the Anode of an LED to the output pin (Middle pin) with a 470 Ohms series resistor.

Connect the Cathode of LED to the ground pin. Connect a 9V battery to the Vcc and Gnd pins observing correct polarity (there is Vcc, Gnd and O/P markings near the pins). When you wave hand in front of the lens, LED will turn on. Adjust the presets clock wise for sensitivity and time delay. It is better to keep the wiper of both the presets in the middle position. You get around 2 minutes delay and 6 meters range in this position. After the time delay, LED turns off. The output can be used to trigger a Buzzer or Relay to make a Burglar alarm or Light switch. See circuits.

Simple PIR Burglar Alarm

When a human movement is detected, buzzer beeps for a fixed time ( as adjusted) then goes off. Ideal circuit to monitor Door and Passages.

PIR Light Switch

Very good Surveillance system for Home. When a human movement is detected, Relay triggers to Turn on light.

How to Fix the circuit.
The finished gadget should be placed on the wall above 2-3 meters from the ground level at an angle of 45 degree. This makes a 45 degree field of view to the ground. Direct Sunlight should not fall on the Sensor. It may cause false triggering. Moving tree branches, sudden fluctuations in temperature and sunlight, fluorescent lamps etc may cause false triggering.

Note : It is better to uses a Transformer power supply for error free working of the PIR sensor Module. Use of Transformerless power supply and cheap SMPS power supply may cause erratic working of the Module. The transients in the Mains lines may cause false triggering.

This is the simplest type of a Tank over flow Alarm circuit that can be used to prevent the overflow of water from the over head tank. Thus it prevents the wastage of water during pumping. The circuit is too simple and its cost is just Rs. 25 including the battery.

Two NPN transistors are used to drive the buzzer and LED to give the overflow alarm. Two probes (two conducting pins or pads ) are fixed at the top of the tank just below the lid of tank. When the water level is below the probes, transistor T1 and T2 will be out of conduction since there is no electrical continuity between the probes. Thus T1 will be cut off due to the lack of base bias. T2 will also be off since T1 is not conducting to give base bias to T2. Buzzer connected to the emitter of T1 and the LED connected to the emitter of T2 will be of off.

When the water level in the tank reaches the probes, electrical conductivity starts between the probes through water. T1 and T2 then conducts to activate the buzzer and LED.
Fix the unit in the room and connect the probes with the circuit using thin wires. Probes can be two pins or two conducting pads like aluminium or copper sheets. The probes should be closely arranged with a gap of 1 cm between them.

You can make this Solar light using only a few components. You need a 3 V Solar panel, two 1.5 V Rechargeable Pen cells and few other components. It is a miniature Portable Solar light that can be placed anywhere like garden, porch or even in an outing place. During day time battery charges from Solar panel and at Sunset, White LED turns on for around 6 hours.

Working of the circuit
Small 3V 100 mA Solar panel is available which costs around Rs.80 only. It delivers around 100 mA current in bright Sunlight to charge the battery. Diode D1 prevents the backward flow of current from the battery to the Solar panel during night. Capacitor C1 acts as a Buffer during charging. During day time, D1 forward biases and current flows from the Solar panel to the battery. At the same time, PNP transistor remains cut off since its base is held high by the current flowing from the solar panel through R1. The 0.5 W White LED connected to the collector of T1 remains off. When the sunlight ceases, base of T1 turns low and it conducts to light the White LED. Thus the solar panel acts like a charger as well as a switch to control T1. You can use any PNP transistor that handles more than 400 mA current.

You can convert the same circuit for 6 volt or 12 volt operations to light 1 W and 3W LEDs. For this use 6 or 12 volt panel and 6 V or 12V Battery. SK 100 can handle up to 800 mA current and 1W and 3W LED consumes around 300 mA current. You can replace SK 100 ( Bel 100 P or CK 100 ) with any Medium power transistor like BD140.