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b.tech mini project on Anti Sleep alarm for Students

This circuit saves both time and electricity for students. It helps to prevent them from dozing off while studying, by sounding a beep at a fixed time interval, say, 30 minutes. If the student is awake during the beep, he can reset the circuit to beep in the next 30 minutes. If the timer is not reset during this time, it means the student is in deep sleep or not in the room, and the circuit switches off the light and fan in the room, thus preventing the wastage of electricity.

The circuit is built around Schmitttrigger NAND gate IC CD4093 (IC1),timer IC CD4020 (IC2), transistors BC547, relay RL1 and buzzer.The Schmitt-trigger NAND gate (IC1) is configured as an astable multivibrator to generate clock for the timer (IC2). The time period can be calculated as T=1.38×R×C. If R=R1+VR1=15 kilo-ohms and C=C2=10 μF, you’ll get ‘T’ as 0.21 second. Timer IC CD4020 (IC2) is a 14-stage ripple counter. Around half an hour after the reset of IC1, transistors T1, T2 and T3 drive the buzzer to sound an intermediatebeep. If IC2 is not reset through S1 at that time, around one minute later the output of gate N4 goes high and transistor T4 conducts. As the outputof gate N4 is connected to the clock input (pin 10) of IC2 through diode D3, further counting stops and relay RL1 energises to deactivate all the appliances.

This state changes only when IC1 is reset by pressing switch S1. Assemble the circuit on a generalpurpose PCB and enclose it in a suitablecabinet. Mount switch S1 and the buzzer on the front panel and the relay at the back side of the box. Place the 12V battery in the cabinet for powering the circuit. In place of the battery, youcan also use a 12V DC adaptor.

Transistorised Code Lock With Torch mini project

This electronic lock for domestic use opens only when you connect the right combination of five switches. There are twelve switches in total. If you connect a wrong combination, the lock remains closed.At night, flip switch S3 to ‘on’ position in order to enable the torch. In the daytime, flip it back to ‘off’ position.

Fig. 1 shows the circuit of the transistorised code lock with torch. For easy understanding, the entire circuit can be divided in three sections: power supply, control and torch.

The power supply section is built around transformer X1, bridge rectifier comprising diodes D1 through D4 and regulator IC 7812 (IC1). The 230V AC, 50Hz AC mains is stepped down by transformer X1 to deliver a secondary output of 15V, 250 mA. The transformer output is rectified by the bridge rectifier, filtered by capacitor C1 and regulated by IC1. Capacitor C2 bypasses the ripples present in the regulated supply. When mains power is available, IC1 provides regulated 12V to the circuit and power-on LED1 glows to indicate that the circuit is enabled.

The control section is built around switches S1 through S12, transistor T1 and relay RL1. Relay driver transistor T1 is used to energise/de-energise the relay.The torch section is built around six white LEDs (LED2 through LED7) and resistors R3 and

R4.Working of the circuit is simple. To open the door, you should know the connection code. Here the connection code is switches S1, S7, S2, S11 and S9. This means you need to connect theses witches to each other by flipping them to ‘on’ position. As the connection completes, transistor T1 conducts and relay RL1 energises. As a result, thedoor lock connected between the pole and normally-open contacts of relay RL1 opens.If you connect a wrong combination, say, switches S4, S10, S11 and S6, transistor T1 does not conduct and relay RL1 remains de-energised. As a result, the door lock remains closed.

Assemble the circuit on a generalpurpose PCB and house it in a small cabinet. Fig. 2 shows the proposed cabinet arrangement for switches and LEDs. Install the cabinet at the front door of your house.

As mentioned in the beginning, switch S3 is used to enable the torch. When it is flipped to ‘on’ position, all the LEDs (LED2 through LED7) glow. Switches S4, S5, S6, S8, S10 and S12 are used just to confuse the intruders and play no role in opening the door. You can also use a 12V battery to power the circuit. In that case, remove transformer X1, diodes D1 through D4, capacitor C1 and regulator IC2 (7812) and connect the battery inside the cabinet with proper polarity.

Sound activated lights mini project

This diy sound activated lights circuit turns a lamp ON for a short duration when the dog barks (or a relatively strong sound) giving an impression that the occupants have been alerted. The condenser microphone fitted in a place to monitor sound and generates AC signals, which pass through DC blocking capacitor C1 to the base of transistor BC549 (T1). Transistor T1 along with transistor T2 amplifies the sound signals and provides current pulses from the collector of T2. When sound is produced in front of the condenser mic, triac1 (BT136) fires, activates lights and the bulb (B1) glows for about two minutes.

Assemble the sound activated lights circuit on a general purpose PCB (circuit board) and enclose in a plastic cabinet. Power to the sound activated switch circuit can be derived from a 12V, 500mA step-down transformer with rectifier and smoothing capacitor. Solder the triac ensuring sufficient spacing between the pins to avoid short circuit. Fix the unit in the dog’s cage or close to the sound monitoring spot, with the lamp inside or outside as desired. Connect the microphone to the sount activated lights circuit using a short length of shielded wire. Enclose the microphone in a tube to increase its sensitivity.

Caution. Since the sound activated lights uses 230V AC, many of its points are at AC mains voltage. It could give you lethal shock if you are not careful. So if you don’t know much about working with line voltages, do not attempt to construct this circuit. We will not be responsible for any kind of resulting loss or damage.

Single-Zone Automatic Burglar Alarm System mini project

The circuit was designed to provide an alarm system against any form of burglary based on the operation of CMOS 4011 where a high output would only result when any of the input is low.

Terminology

Zone – refers to an alarm control panel’s input from a protective circuit which divides the alarm system into separate independent areas of protection based on function which may include medical, fire, intrusion, or critical condition monitoring

Burglar Alarm - one way of preventing break-in’s into one’s property, not only to protect the possessions but the occupants as well; can prevent the havoc and disruption caused by theft and break-in’BC547 – NPN small signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selections CMOS 4011 – a quad 2-input NAND gate integrated circuit, generally characterized by small fluctuation in voltage supply, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption

The zone designed in this circuit contains automatic entry and exit intervals with a bell having its cut off timer. It can also be applicable to other normally open and normally closed switches that contains input devices such as magnetic reed contacts, pressure mats, foil tapes, inertia sensors and passive infrared detectors. The buzzer will sound if the alarm is switched on wherein the loop is in open stage. On theother hand, as the switch turns off, the loop becomes a closed circuit again. The alarm will operate with any type of two-way switch.

The circuit is being powered by a 12 V supply, which is enough for as long as the buzzer, siren, and relay will match the supply input. The basicoperation of the alarm occurs with the interruption of electric current to a relay cause by deenergizing of the relay and making the relay contacts to operate the alarm indicator. The circuit is applicable to a single zone which can consist of a single point of contact. To start the circuit to function, the switch S1 should be set accordingly, but before doing this, all the LED should be properly lighting. Once the switch has been set, there will be an allotted thirty seconds to leave the premises which will trigger the buzzer to sound. It will only stop sounding when the door has been closed. In doing this procedure, it will ensure that the entry and exit operation has been restored effectively. Upon re-entering the premises, there will be 30 seconds time allotment to turn OFF the switch SW1. Failing to do this will trigger and energize the relay and eventually sound the siren. This can be deactivated at any time by turning OFF SW1. The alarm will reset, the relay will de-energize, and the siren will be cut-off once the loop has been restored after 15 minutes.

The delay timers in the circuit depend largely on the values and characteristics of the components used in the circuit, due to the manufacturing tolerances. The entry, exit and bell cut-off timer can be modified by altering the values of resistors R9, R6 and R3 depending on the prerequisite. By decreasing the values, the timer will also decrease; same thing with increasing the values will increase the timing.

Application:

A burglar alarm system helps detect unauthorized entry onto a company’s premises. The system sends a signal to a central monitoring center when activated. The monitoring centers provide 24/7 service and will alert the local police to dispatch authorities to the scene. It is a proven fact that the risk of burglary is significantly reduced after a burglar alarm is installed.

sound operated switch with a relay driver mini project

This sensitive sound operated switch can be used with a dynamic microphone insert as above, or be used with an electret (ECM) microphone. If an ECM is used then R1 (shown dotted) will need to be included. A suitable value would be between 2.2k and 10kohms.

The two BC109C transistors form an audio preamp, the gain of which is controlled by the 10k preset. The output is further amplified by a BC182B transistor. To prevent instability the preamp is decoupled with a 100u capacitor and 1k resistor. The audio voltage at the collector of the BC182B is rectified by the two 1N4148 diodes and 4.7u capacitor. This dc voltage will directly drive the BC212B transistor and operate the relay and LED. It should be noted that this circuit does not “latch”. The relay and LED operate momentarily in response to audio peaks.

The gain of the circuit and sensitivity is controlled by the 10k variable resistor on the emitter of the first (left hand side) transistor. A preset may be used if gain is fixed, a potentiometer should be used to trigger at different sound levels.The relay contacts close and then open (momentary action) in response to audio peaks, these can be used to switch other circuit. The diode across the relay is the usual back emf diode and a 1N4003 or 1N4004 will work well here, preventing damage to the transistor.

mini project on Pyroelectric fire alarm

Here is an ultra-sensitive fire sensor that exploits the direct piezoelectric property of an ordinary piezo element to detect fire. The lead zirconate titanate crystals in the piezo element have the property to deform and generate an electric potential when heated, thus converting the piezo element into a heat sensor. The circuit described here is very sensitive. It gives a warning alarm if the room temperature increases more than 10°C

Sensor side circuit. Fig. 1 shows the fire sensor circuit. The front end of the circuit has a sensitive signal amplifier built around IC1 (CA3130). It gives a high output when temperature near the piezo element increases. IC CA3130 is a CMOS operational amplifier with gate protected p-channel MOSFETs in the inputs. It has high speed of performance and low input current requirements. There are two inputs—the non-inverting input (pin 3) connected to the piezo element through diode D7 (OA71) that carries the voltage signal from the piezo element and the inverting input (pin 2) that gets a preset voltage through VR1.

By adjusting VR1, it is easy to set the reference voltage level at pin 2. In normal condition, IC1 gives a low output and the remaining circuitry is in a standby state. Capacitor C2 keeps the non-inverting input of IC1 stable, so that even a slight change in voltage level in the inputs can change the output to high.Normally, IC1 gives a low output, keeping transistor T1 non-conducting. Reseting pin 12 of IC2 (CD4060) connected to the collector of transistor T1 gets a high voltage through R5 and IC2 remains disabled. When the piezo element gets heat from fire, asymmetry in its crystals causes a potential change, enabling capacitor C2 to discharge. It momentarily changes the voltage level at pin 3 of IC1 and its output swings high. Transistor T1 conducts taking the reset pin 12 of IC2 to ground. IC2 is now enabled and starts oscillating. With the shown values of the oscillating components C3 (0.22μ) and R6 (1M), the first output (Q3) turns high after a few seconds and a red LED2 starts flashing. If heat near the piezo persists, Q7 (pin 14) output of IC2 becomes high after one minute, and the alarm starts beeping. If heat continues, Q9 (pin 15) turns high after four minutes and turns on the relay driver transistor T2. At the same time, diode D8 conducts and IC2 stops oscillating and toggles.

The solenoid pump connected to the N/O (normally opened) contact of the relay starts spraying the fire-ceasing foam or water to the possible sites of fire.

Power supply circuit. Power supply section (Fig. 2) comprises a 0-12V, 1A step-down transformer with a standard full-wave rectifier formed by D1 through D4 and filter capacitor C1. A battery backup is provided if the mains supply is cut-off due to short-circuit and fire. A 12V, 4.5Ah rechargeable battery is used for backup to give sufficient current to the solenoid pump. When mains

power is available, diode D5 forward biases. It provides power to the circuit and also charges the battery through resistor R2, and it limits the charging current to 120 mA. When power fails, diode D5 reverse biases and diode D6 forward biases, giving instant backup to the circuit. LED1 indicates the availability of mains power.

Assemble the circuit on a generalpurpose PCB and enclose it in a suitable case. Connect the piezo element to the circuit using a thin insulated wire. Glue the flat side of the piezo element on a 30×30cm aluminium sheet to increase its sensitivity. Fix the sheet with the piezo sensor to the site where protection is needed. The remaining circuit can be fixed at a suitable place. If only the alarm generator is needed, omit the relay driver section.

(DTMF) TELEPHONE-OPERATED CALLING SYSTEM mini project

This telephone-operated calling circuit is very helpful for doctors in calling the patients, in banks and in various other situations where persons have to be called or signalled. When you need to call a person amongst many standing outside your cabin, just lift the telephone handset off the cradle and press the respective number. The number of the person called will be displayed and a bell will sound to inform the person that it is his turn.

Dual-tone multiple-frequency (DTMF) receiver IC is commonly used in telephone equipment. One common DTMF receiver is Holtek HT9170 used in electronic communication circuits. The Holtek HT9170 series comprises DTMF receivers integrated with digital decoder and bandsplit filter functions. All HT9170 series ICs use digital counting techniques to detect and decode all the 16 DTMF tone pairs into a 4-bit code output.The circuit can also be used in quiz contests and by visually- or hearingimpaired people. It can be used to call a maximum of nine different persons. The circuit is built around DTMF receiver IC HT9170, BCD-to-7-segment decoder/driver 7447, quad 2-input OR gate and common-anode display. Simple melody generator IC UM66 is used to produce melody sound in the loudspeaker through Darlington-pair transistors (T1 and T2).The tone pair DTMF generated by pressing the telephone key is converted into binary values internally in the IC. The binary values are indicated by the glowing of LEDs at the output of IC1.

The output of IC1 is connected to:

· LEDs connected via resistors R15 through R18 at pins 11 through 14, respectively. LED1 indicates the LSB and LED4 indicates the MSB.

· BCD-to-7-segment decoder/ driver 7447, whose outputs are connected to the common-anode display for displaying the pressed number on the telephone connected in parallel to the circuit.

· Gates N1 and N2 to activate the call bell.

Here is how the circuit works: Connect the telephone and the circuit in parallel to the telephone line. Connect 6V to the circuit. When you press switch S1, DIS1 shows ‘0.’ Lift the handset off the cradle and dial a number, say, ‘1.’ The output of IC1 becomes A3A2A1A0 = 0001. LED1 glows, the display shows ‘1’ and the call bell sounds.To stop the call bell, put the receiver on the cradle and press switch S1 momentarily. Now DIS1 shows ‘0’ and LED1 stops glowing.For calling other numbers, follow the same procedure: Lift the handset off the cradle and press the desired number (0 through 9). The respective LED will glow, the number will be displayed on DIS1 and the call bell will sound. Now put the handset on the cradle and press S1 momentarily to stop the call bell.

Emergency Light mini project

This is an LDR based Emergency Lamp that turns on a High watt White LED when there is darkness in the room. It can be used as a simple emergency lamp in the child’s room to avoid the panic situation in the event a sudden power failure.It gives ample light in the room.

The circuit is too simple so that it can be enclosed in a small box. A 12 volt miniature battery is used to power the circuit. Two transistors T1 and T2

are used as electronic switches to turn on / off the white LED. When there is sufficient light in the room, LDR conducts so that the base of the PNP transistor T1becomes high and it remains off. T2 also remains off since its base is grounded. In this state, White LED remains off. When the light falling on the LDR decreases, it cease to conduct and T1 forward bias providing base current to T2. It then turns on and White LED switches on.White LED used in the circuit is 1 watt High bright Luxeon LED . Since 1 watt White LED consumes around 300 milli ampere current, it is better to switch off the lamp after few minutes to conserve battery power

Ethernet Controller kit mini project

This circuit is an ETHERNET controller I use the PIC18F452 and the mikroC C Compiler. I use also the JAVA SCRIPT information you can get from www.w3school.com I Control 8 outputs throw the WEB and transfer time information also.

I use 3 timer and 3 buffers each one has its own time Start Stop and the outputs will take the buffer BIN value

BUFFER 1 -> TIMER 1

BUFFER 2 -> TIMER 2

BUFFER 3 -> TIMER 3

I do all the adjustment throw the WEB. I also test it to transfer temperature information using DS1820 temp. Sensor. I Set time-date throw the WEB

Features:

1. Display time (DS1307), with backup battery.

2. Control 8 outputs

3. 3 timers to control the outputs each timer has separate time for start and stop

4. All the adjustment throw the WEB

Schematic:

PCB

Web Browser screenshoots

Electronic Card- Lock System mini project

The circuit presented here can beused as a lock for important electronic/ electrical appliances. When card is inserted inside its mechanism, depending upon the position of punched hole on the card, a particular appliance would be switched on. The card is inserted just like a floppy disk inside the disk drive. This card should be rectangular in shape with only one punched hole on it.

The circuit uses eight photo-transistors (T1 through T8). When there is no card in the lock, light from incandescent lamp L1 (40- watt, 230V) falls on all the photo- transistor detectors. Transistor T8 is used as enable detector for IC1 (74LS244). When light is incident on it, it conducts and its collector voltage goes low. This makes transistor T16 to cut-off, and its collector voltage goes high. This logic high on its collector terminal will inhibit IC1 as long as light is present on photo-transistor T8.

IC1 will get enabled only when the card is completely inserted inside the lock mechanism. This arrangement ensures that only the selected appliance is switched on and prevents false operation of the system.You can make these cards using a black, opaque plastic sheet. A small rectangular notch is made on this card to indicate proper direction for insertion of the card. If an attempt is made to insert the card wrongly, it will not go completely inside the mechanism and the system will not be enabled.

When card for any appliance (say appliance 1) is completely inserted in the mechanism, the light will fall only on photo-transistor T1. So only T1 will be on and other photo-transistors will be in off state. When transistor T1 is on, its collector voltage falls, making transistor T9 to cut-off. As a result, collector voltage of transistor T9 as also pin 2 of IC1 go logic high. This causes pin 18 (output Q1) also to go high, switching LED1 on. Simultaneously, output Q1 is connected to pin 1 of IC2 (ULN2003) for driving the relay corresponding to appliance 1. Similarly, if card for appliance 2 is inserted, only output pin 16 (Q2) of IC1 will go high—making LED2 on while at the same time energising relay for appliance 2 via ULN2003. The same is true for other cases/appliances also.

The time during which card is present inside the mechanism, the system generates musical tone. This is achieved with the help of diodes D1 through D7 which provide a wired-OR connection at their common-cathode junction. When any of the outputs of IC1 is logic high, the common-cathode junction of diodes D1 through D7 also goes logic high, enabling IC3 (UM66) to generate a musical tone.

In this circuit IC1 (74LS244) is used as buffer with Schmitt trigger. All outputs (Q1 through Q7) of this IC are connected

Electronically Lock for door by keybad mini project

The circuit was constructed to provide a simple electronic lock system based on a single integrated circuit and will require a code of seven digits.

Terminology

4022 – a 4-stage CMOS counter with 8 decoded outputs used for binary counter/decoder, divide-by-N counting, frequency division, decade counter/decimal decode display, and counter control/timers due to its features such as standardized symmetrical output characteristics, medium speed operation, parametric ratings (5V, 10V, 15V), 100% tested for quiescent current at 20V, and fully static operation
BS170 – an N-channel enhancement mode field effect transistor designed to minimize on-state resistance while providing reliable, rugged, and fast switching performance and particularly suited for low voltage, low current application such as power MOSFET gate drivers and small servo motor control due to its features of high saturation current capability, voltage controlled small signal switch, and high density cell design
BD679 – a monolithic NPN Silicon epibase power Darlington transistor with resistors and diode in a TO 126 plastic package and is typically used for AF applications due to its high current gain

Circuit Explanation:

The construction of the circuit is relatively simple since it utilizes a very few components. One important thing to be considered in doing this circuit is the time it will take, after the push button switches are pressed, for the code to reach the main IC. There will be a delay unless all the keys were entered. When the right sequence of code was entered correctly, the output of Q7 will be activated for approximately 4 seconds. This will drive the transistor Q2 which in turn would drive one relay that will open the door or any other circuit attached.

The use of red LED D3 provides a visual indication of the activation of Q2. The code that has been set for the circuit is 1704570, as seen in the diagram. This was made possible by the arrangement of the resistors with their corresponding connections to the switches. The resistors are arranged from points A to G order while the switches are connected to the corresponding resistors in random order. The security code can be changed by altering the connections between the switches and the outputs of the IC1.

Part List

R1-7=4.7Kohm
R8=15Kohm
R9=1Mohm
R10-13=10Kohm
R11=100ohm

R12=220Kohm
R14=1.2Kohm
C1-3=100nF 100V
C2=4.7uF 25V
D1-2=1N4148

D3=RED LED 3mm
IC1=4022
Q1=BS170
Q2=BD679
S1-10=Push button or keyboard

Application

In most secured places with the capability of the company to purchase high end equipments, an electronic key operated door is usually installed. This will prohibit the entry of unauthorized persons or verify the entrance of a person by supplying the correct key code. This electronic security door key may also be found on vehicle doors for locking and unlocking purposes. Other establishments that utilize this are jewelry shops, banks, apartments, factories, hotels, prisons, apartments, and homes. They are very reliable since they are convenient to use and can be integrated easily with other circuitries

speed control Temperature DC fan mini project

Here is a simple circuit based on two transistors that can be used to control the speed of a 12 V DC fan depending on the temperature.A thermistor (R1) is used to sense the temperature.

When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 more and so do the speed of the motor. Also, the brightness of the LED will be proportional to the speed of the motor.

Circuit diagram with Parts list:

Notes.

The R1 can be a 15K @ 20°C ,N.T.C thermistor.

The M1 can be a 12V,700mA fan motor.

The capacitor C1 must be rated 25V.

The circuit can be powered from a 12V PP3 battery or 12V DC power supply.

Assemble the circuit on a good quality PCB or common board.

mini projects for electronics & electrical branches

B.TECH MINI PROJECTS OF ELECTRICAL AND ELECTRONICS BRANCHES

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Servo Motor Controller mini project

This is the simple basic design of Servo pulse generator. It uses the CMOS IC 7555 in the Astable mode to generate pulses to drive the servo motor. The circuit can be suitably modified to get pulses of sufficient length.

A Servo is a small device that has an output shaft. This shaft can be positioned to specific angular positions by sending the servo a coded signal. As long as the coded signal exists on the input line, the servo will maintain the angular position of the shaft. The angular position of the shaft is determined by the duration of a pulse that is applied to the control wire. This is called Pulse Coded Modulation.

The servo typically requires pulse every 20 milliseconds (.02 seconds). The length of the pulse will determine how far the motor turns. Generally, 1.5 millisecond pulse will make the motor turn to the 90 degree position. This is called the Neutral Position. If the pulse is shorter than 1.5 ms, the motor will turn the shaft to close to 0 degrees. If the pulse is longer than 1.5ms, the shaft turns closer to 180 degrees.

M7555Datasheet
The circuit is designed to give control signals to the Servo.IC1 is designed as an Astable multi vibrator which can give pulses for the operation of the Servo. The 10KPot VR2, R1 and capacitor C1 determines the High and Low time of pulses. Since VR2 is variable, High time varies from 2.07 mS to 1.03 mS. The low time will be 40.5 mS. By adjusting VR1, it is easy to get exact timing.VR3 adjust the control voltage of 1.6 volts to the control pin 5 of IC1.

Servo Motor:

A control voltage can also be supplied from outside. Then VR3 should be omitted. The control volt can be provided from a variable power supply that gives output of 0-10 volts. The control voltage will control the position of the servo motor connected to the output. When the control voltage changes, the servo will move to the new position corresponding to the new control voltage value. 0 volt causes the servo to remain at one end and 10 volts to other end. If the control volt is 5 volts the servo remains in the center position.

CURRENT SENSOR mini project

High-wattage appliances like electric irons, ovens and heaters result in unnecessary power loss if left ‘on’ for hours unnoticed. Here is a circuit that senses the flow of current through the appliances and gives audible beeps every fifteen minutes to remind you of power-’on’ status. This is a non-contact version of current monitor and can sense the flow of current in high-current appliances from a distance of up to 30 cm . It uses a standard step-down transformer (0-9V, 500mA) as the current sensor. Its secondary winding is left open, while the primary winding ends are used to detect the current. The primary ends of the transformer are connected to a full-wave bridge rectifier comprising diodes D1 through D4. The rectified output is connected to the non-inverting input of IC CA3140 (IC1).IC CA3140 is a 4.5MHz BIMOS operational amplifier with MOSFET input and bipolar transistor output. It has gate-protected MOSFET (PMOS) transistors in the input to provide very high input impedance (1.5 T-ohms), very low input current (10 pA) and high-speed switching performance.

The inverting input of IC1 is preset with VR1. In the standby mode, the primary of the transformer accepts e.m.f. from the instrument or surrounding atmosphere, which results in low-voltage input to IC1. This low voltage at the non-inverting input keeps the output of IC1 low. Thus transistor T1 doesn’t conduct and pin 12 of IC2 goes high to disable IC2. As a result, the remaining part of the circuit gets inactivated.When a high-current appliance is switched on, there will be a current drain in the primary of the transformer to the negative rail due to an increase in the e.m.f. caused by the flow of current through the appliance. This results in voltage rise at the non-inverting input and the output of IC1 becomes high. This high output drives transistor T1 into conduction and the reset pin of IC2 becomes low, which enables IC2.

IC CD4060 (IC2) is a 14-stage ripple counter. It is used as a 15-minute timer by feeding Q9 output to the piezobuzzer for aural alarm through the intermediate circuitry. Resistors R5 and R6 along with capacitor C1 maintain the oscillations in IC2 as indicated by blinking LED1. The high output from IC2 is used to activate a simple oscillator comprising transistors T2 and T3, resistors R8 and R10, and capacitor C2.

When the Q9 output of IC2 becomes high, zener diode ZD1 provides 3.1 volts to the base of transitor T2. Since transistor T2 is biased by a highvalue resistor (R8), it will not conduct immediately. Capacitor C2 slowly charges and when the voltage at the base of T2 increases above 0.6 volt, it conducts. When T2 conducts, the base of T3 turns low and it also conducts. The piezobuzzer connected to the collector of T3 gives a short beep as capacitor C2 discharges. This sequence of IC2 output at Q9 becoming high and conduction of transistors T2 and T3 resulting in beep sound repeats at short intervals.

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