Boomerang

Materials:

ü  A. 1/4" birch plywood, 20" x 16"

ü  B. Pattern Download.pdf

ü  C. Spray paint or clear lacquer

ü  D. Coping saw or scroll saw

ü  E. Sanding block or orbital sander

 

how-to:

 ü  Trace your pattern onto the plywood and use a saw to cut out the shape.

ü  Use a sanding block (and a lot of elbow grease) or an orbital sander to give each side of the boomerang an airfoil shape. The direction the airfoil faces depends on the hand with which you throw.

ü  In the middle of the boomerang blend the two airfoils together. You want the whole surface to be smooth.

ü  Give it a final sanding with fine grit paper then apply a thin coat of spray paint or clear lacquer to help protect the boomerang and make it look nice.

ü  Now you are ready to throw it. Find a very large, open space (at least a full baseball field). Hold nly the very tip of the boomerang in your throwing hand. You should throw the boomerang nearly vertical but angled outward sligtly. Aim just above the horizon. Throw it hard and overhand like a baseball and flick your wrist as you let go.

ü  Go fetch the boomerang. It will take some practice and experimentation before you can get it to come right back to you.

Midnight Security Light

Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical’ sleep.
          Here is an energy-saving circuit that causes the thieves to abort the theft attempt by lighting up the possible sites of intrusion (such as kitchen or backyard of your house) at around 1:00 am. 
It automatically resets in the morning.
For this you need:
1) bridge rectifier
2) transformer i.e voltage regulator
3)  IC (ic cd  4060)
4) LDR
5) LED & bulb
6) Capacitor & resistance
7) TRIAC 

The circuit is fully automatic and uses a CMOS IC CD 4060 to get the desired time delay. Light-dependent resistor LDR1 controls reset pin 12 of IC1 for its automatic action. During day time, the low resistance of LDR1 makes pin 12 of IC1 ‘high,’ so it doesn’t scillate. After sunset, the high resistance of LDR1 makes pin 12 of IC1 ‘low’ and it starts oscillating, which is indicated by the flashing of LED2 connected to pin 7 of IC1. The values of oscillator components (resistors R1 and R2 and capacitor C4) . are chosen such that output pin 3 of IC1 goes ‘high’ after seven hours, i.e., around 1 am. This high output drives triac 1 (BT136) through LED1 and R3.
            Bulb L1 connected between the phase line and M2 terminal of triac 1 turns on when the gate of triac 1 gets the trigger voltage from pin 3 of IC1. It remains ‘on’ until pin 12 of IC1 becomes high again in the morning. Capacitors C1 and C3 act as power reserves, so IC1 keeps oscillating even if there is power interruption for a few seconds. Capacitor C2 keeps trigger pin 12 of IC1 high during day time, so slight changes in light intensity don’t affect the circuit. Using preset VR1 you can adjust the sensitivity of LDR1.
            Power supply to the circuit is derived from a step-down transformer X1 (230V AC primary to 0-9V, 300mA secondary), rectified by a full-wave rectifier comprising diodes D1 through D4 and filtered by capacitor C1. Assemble the circuit on a general purpose PCB with adequate spacing between the components. Sleeve the exposed leads of the components.
Using switch S1 you can turn on the lamp manually. Enclose the unit in a plastic case and mount at a location that allows adequate daylight.
           Caution. Since the circuit 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. EMP(Engineering mini project.blogspot.com)  will not be responsible for any kind of resulting loss or damage.

Antisleep 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.

Things Needed for Making this Antisleep Alarm for Students

• Relay
• Bulb
• Transistor or SCR
• Push to ON /OFF switches
• Resistance & capacitor
• Piezzo buzzer
• Diode
• IC: IC CD4020

           The circuit is built around Schmitt trigger 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 intermediate beep. 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 output of gate N4 is connected to the clock input (pin 10) of IC2 through diode D3, further counting stops and relay RL1 energies to deactivate all the appliances. This state changes only when IC1 is reset by pressing switch S1. 
          Assemble the circuit on a general-purpose PCB and enclose it in a suitable cabinet. 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, you can also use a 12V DC adaptor.

Shadow Detector (Short Range Hand Wave Detector)

                  The circuit below works quite well in typical indoor room lighting. I would not recommend its use in direct sunlight. Two small PIN photo diodes positioned about one inch apart form a shadow detector. With no shadow cast on the devices, both devices produce nearly identical current levels. The current is converted to a voltage with two load resistors in parallel with the photo diode. One resistor is adjustable to the two voltages can be carefully balanced under uniform lighting. When a hand or an arm is moved over the sensors, casting a shadow, one device will detect more light than the second, as the shadow moves over the two sensors. 
             
             
               
               
             This triggers an imbalance. A voltage  comparator connected to the two devices detects the imbalance and sends a high logic level signal to an n-channel FET, which can turn on a beeper or activate a relay. If a low power voltage comparator is used, such as the LMC7211, a 9 volt battery will power the circuit for many years. The more popular LM358 would also work but would draw more current.

SIMPLE DIGITAL SECURITY SYSTEM

You can use this simple and reliable security system as a watchdog by installing the sensing loops around your building. You have to stretch the loop wires two feet above the ground to sense the unauthorized entry into your premises. Wire loops 1, 2 and 4 are connected to the A, B and C inputs of 7-segment decoder 4511 (IC1), respectively, while the D input of IC1 is grounded permanently.

The loops are also connected to a dual 3-input NOR gate and inverter CD4000 (IC2) to activate the alarm. Fig. 1 shows the circuit of the digital security system, while Fig. 2 shows the proposed wiring diagram for the loops around the premises. Before using this security system, make sure that loops shown in Fig. 2 are connected as shown in Fig. 1. If you don’t want to use a buzzer, switch it off by opening switch S2. The circuit works off a 9V regulated power supply. However, battery back-up is recommended. A commoncathode, 7-segment display (LTS543) is used for displaying whether the

loops are intact or not. If loop 1 is broken, the display will show ‘1’. If two or all the three loops are broken, the display will show the sum of the respective broken loop numbers. For example, if loops 1 and 4 are broken, the display will show 5(1+4).

When all the three loops are intact, the display will show ‘0.’ All the three inputs of gate N1 remain low to give a high output. This high output is further given to gate N2 and, as a result, its output remains low. This keeps transistor T1 in cut-off position and the piezobuzzer does not sound.

When any loop is broken, the output of NOR gate N1 goes low, while the output of gate N2 goes high. Transistor T1 conducts and the buzzer sounds to alert you. You can mute the buzzer by switching off power to the circuit through switch S1.

Wireless switch

Normally, home appliances are controlled by means of switches,

sensors, etc. However, physical contact with switches may be

dangerous if there is any shorting .So here a tip about how to prepare

a wireless switchs

To prepare Wireless switch  we need

• Transistor / SCR
• LED
• Relay
• Resistor and Capacitor
• IC CA 3140

  

The circuit described here requires no physical contact for operating the appliance. You just need to move your hand between the infrared LED (IR LED1) and the phototransistor (T1). The infrared rays transmitted by IR LED1 is detected by the photo transistor to activate the hidden lock, flush system, hand dryer or else.

            This circuit is very stable and sensitive compared to other AC appliance control circuits. It is simple, compact and cheap. Current consumption is low in milliamperes. The circuit is built around an IC CA3140, IRLED1, photo transistor  and other discrete components. 
           When regulated 5V is connected to the circuit, IR LED1 emits infrared rays, which are
received by phototransistor T1 if it is properly aligned. The collector of T1 is connected to non-inverting pin 3 of IC1. Inverting pin 2 of IC1 is connected to voltage-divider preset VR1. Using preset VR1 you can vary the reference voltage at pin 2, which also affects sensitivity of the phototransistor. Op-amp IC1 amplifies the signal received from the phototransistor. Resistor R3 controls the base current of transistor BC548 (T2). The high output of IC1 at pin 6 drives transistor T2 to energies relay RL1 and switch on the appliance, say, hand dryer, through the relay contacts.

             The working of the circuit is simple. In order to switch on the appliance, you simply interrupt the infrared rays falling on the phototransistor through your hand. During the interruption, the appliance remains on through the relay. When you remove your hand from the infrared beam, the appliance turns off through the relay.

              Assemble the circuit on any general- purpose PCB. Identify the resistors through colour coding or using the multimeter. Check the polarity and pin configuration of the IC and mount it using base. After soldering the circuit, connect +5V supply to the circuit  

Home made Solar cells Power generator

Solar cells generate direct current,so make sure that DPDT switch S1 is towards the solar panel side. The DC voltage from the solar panel is used to charge the battery and control the relay.Capacitor C1 connected in parallel with a 12V relay coil remains charged in daytime until the relay is activated.Capacitor C1 is used to increase the response time of the relay, so switch-ing occurs moments after the voltage across it falls below 12V. Capacitor C1 also filters the rectified output if the battery is charged through AC power.The higher the value of the capacitor,the more the delay in switching.

The switching time is to be properly adjusted because the charging wouldpractically stop in the early evening while we want the light to be ‘on’ during late evening.During daytime, relay RL1 energises, provided DPDT switch S1 is towards the solar panel side. Due to energisation of relay RL1, the positive terminal of the battery is connected to the output of regulator IC 7808 (a 3-terminal, 1A, 8V regulator) via diode D1 and normally-open (N/O) contacts of relay RL1. Here we have used a 6V, 4.5Ah maintenance-free, lead-acid rechargeable battery. It requires a constantvoltage of approx. 7.3 volts for its proper charging.Even though the output of the solar panel keeps varying with the lightintensity, IC 7808 (IC1) is used to give a constant output of 8V. Diode D1 causes a drop of 0.7V, so we get approx. 7.3V to charge the battery.

LED1 indicates that the circuit is working and the battery is in the charging mode.At night, there will be no generation of electricity. The relay will not energise and charging will not take place. The solar energy stored in thebattery can then be used to light up the lamp. A 3W lamp glows continuously for around 6 hours if the battery is fully charged. Instead of a 3W lamp, you can also use a parallel array of serially connected white LEDs and limiting resistors to provide sufficient light for even longer duration. In case the battery is connected in reverse polarity while charging, IC 7808 will get damaged. The circuit indicates this damage by lighting up LED2, which is connected in reverse with resistor R2. However, the circuit provides only the indication of reverse polarity and no measure to protect the IC. A diode can be connected in reverse to the common terminal of the IC but this would reduce the voltage available to the battery for charging by another 0.7 volt.There is also a provision for estimating the approximate voltage in the battery. This has been done by connecting ten 1N4007 diodes (D2 through D11) in forward bias with the battery.

The output is taken by LED3 across diodes D2, D3, D4 and D5, which is equal to 2.8V when the battery is fully charged. LED3 lights up at 2.5 volts or above. Here it glows with the voltage drop across the four diodes, which indicates that the battery is charged. If the battery voltage falls due to prolonged operation, LED3 no longer glows as the drop across D2, D3, D4 and D5 is not enough to light it up. This indicates that the battery has gone weak. Microswitch S1 has been provided to do this test whenever you want. If the weather is cloudy for some consecutive days, the battery will not charge. So a transformer and full-wave rectifier have been added to charge the battery by using DPDT switch S1. This is particularly helpful in those areas where power supply is irregular; the battery can be charged whenever mains power is available