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 unauthorised 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.

Motion Sensor for security Light

Here is a system based on PIR motion detector module BS1600 (or BS1700) that can be used for security or corridor lighting in power saving mode.
The 12V DC power supply required for the motion detector and the relay driver is derived from 230V, 50Hz mains using a transformerless circuit as shown in Fig. 1. The working of the circuit is simple. When you power-on the circuit after assembling all the components including the CFL, the CFL will glow for 10 seconds, turn off for 30 seconds, glow for 10 seconds and then turn off.
Now the circuit is ready to work.
When any movement is detected, around 3.3V appears on the base of relay-driver transistor T1 and it conducts to energise relay RL1. As a result, Triac1 (BT136) fires to provide full 230V and light up the CFL. Another normally-opened contact of the relay (N/O2) is used here to hold the output until reset. If the switch is not in ‘hold’ position, the light will remain ‘on’ for about ten seconds (as programmed in the motion sensor). In short, when there is a movement near the sensor, the CFL glows for about ten seconds. It will remain ‘on’ if switch S1 is in ‘hold’ position. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Use a three-pin connector for connecting the PIR sensor in the circuit with correct polarity. The motion detector is embedded onto the transparent cover of the light assembly
as shown in Fig. 2

An arrangment of CFL assembly in the author’s prototype (Fig. 3) is shown in Fig. 4. In this arrangement, a PIR sensor and 23W, 230V AC CFL are used. Seal all four sides with Blue Tac for water-tightness. Insulate the track side of the PCB using an insulating foam and glue to the base.

IR Level Detector

"Useful for liquids level detection and proximity devices

Up to 50 cm. range, optional relay operation"

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range can be set from a couple of cm. to about 50 cm. by means of a trimmer.

Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device's sensitivity.

R1_____________10K 1/4W Resistor

R2,R5,R6,R9_____1K   1/4W Resistors
R3_____________33R   1/4W Resistor
R4,R8___________1M   1/4W Resistors
R7_____________10K   Trimmer Cermet
R10____________22K   1/4W Resistor
C1,C4___________1µF  63V Electrolytic or Polyester Capacitors
C2_____________47pF  63V Ceramic Capacitor
C3,C5,C6______100µF  25V Electrolytic Capacitors
D1_____________Infra-red LED
D2_____________Infra-red Photo Diode (see Notes)
D3,D4________1N4148  75V 150mA Diode
D5______________LED  (Any color and size)
D6,D7________1N4002  100V 1A Diodes
Q1____________BC327  45V 800mA PNP Transistor
IC1_____________555  Timer IC
IC2___________LM358  Low Power Dual Op-amp
IC3____________7812  12V 1A Positive voltage regulator IC
RL1____________Relay with SPDT 2A @ 220V switch
            Coil Voltage 12V. Coil resistance 200-300 Ohm
J1_____________Two ways output socket

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses  at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing  the target on the same line, a couple of centimeters apart, on a short  breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected  by the surface placed in front of it. The signal is amplified by IC2A and peak  detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward  diode drop of D4. A DC voltage proportional to the distance of the reflecting  object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. 

This comparator switches on and off the LED and the optional relay via Q1,  comparing its input voltage to the reference voltage at its non-inverting input  set by the Trimmer R7.

Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.

Current drawing: LED off 40mA; LED and Relay on 70mA @ 12V DC supply.
R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.

The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.

Avoid sun or artificial light hitting directly D1 & D2.
Usually D1-D2 optimum distance lies in the range 1.5-3 cm.

Auto-matic Heat Detector

The components need to prepare this:

• Transistor
• Resistor & capacitor
• Loudspeaker
• IC UM3561
• Relay
• Zener diode
• Diode
• LED 

This circuit uses a complementary pair comprising npn metallic transistor T1 (BC109) and pnp germanium transistor T2 (AC188) to detect heat (due to outbreak of fire, etc) in the vicinity and energise a siren. The
collector of transistor T1 is connected to the base of transistor T2, while the collector of transistor T2 is connected to relay RL1.

The second part of the circuit comprises popular IC UM3561 (a siren and machine-gun sound generator IC), which can produce the sound of a fire-brigade siren. Pin numbers 5 and 6 of the IC are connected to the +3V supply when the relay is in energised state, whereas pin 2 is grounded. A resistor (R2) connected across pins 7 and 8 is used to fix the frequency of the inbuilt oscillator.

  

The output is available from pin 3. Two transistors BC147 (T3) and BEL187 (T4) are connected in Darlington configuration to amplify the sound from UM3561. Resistor R4 in series with a 3V zener is used to provide the 3V supply to UM3561 when the re-lay is in energised state. LED1, connected in series with 68-ohm resistor R1 across resistor R4, glows when the siren is on. To test the working of the circuit, bring a burning matchstick close to transistor T1 (BC109), which causes the resistance of its emitter-collector junction to go low due to a rise in temperature and it starts conducting. Simultaneously, transistor T2 also conducts because its base is connected to the collector of transistor T1. As a result, relay RL1 energises and switches on the siren circuit to produce loud sound of a firebrigade. EMP Lab note.

We have added a table to enable readers to obtain all possible sound effects by returning pins 1 and 2 as suggested in the table.

Medium Power FM Transister

The components need to prepare it are:
    * Coil (Inductance +reluctance) .
    * Capacitor.
    * Resistor.
    * Mic.
    * ON OFF switch .
    * Transistor .
    * Antenna ( it doesn't need any element just straight wire act as antenna ).The range of this FM transmitter is around 100 metres at 9V
DC supply.
The circuit comprises three stages. The first stage is a microphone preamplifier

built around BC548 transistor. The next stage is a VHF oscillator wired around another BC548. (BC series transistors are generally used in low-frequency stages. But these also work fine in RF stages as oscillator.) The third stage is a class-A tuned amplifier that boosts signals from the oscillator. Use of the additional RF amplifier increases the range of the transmitter. 

Coil L1 comprises four turns of 20SWG enamelled copper wire wound to 1.5cm length of a 4mm dia. air core. Coil L2 comprises six turns of 20SWG enamelled copper wire wound on a 4mm dia. air core.
Use a 75cm long wire as the antenna. For the maximum range, use a sensitive receiver. VC1 is a frequency-adjusting trimpot. VC2 should be adjusted for the maximum range. The transmitter unit is powered by a 9V PP3 battery. It can be combined with a readily available FM receiver kit to make a walkie-talkie set as shown in Fig. 3.


This is only transmitter we have posted  receiver to complete full walkie-talkie see the Medium Power FM Transister

IR Music Transmitter & Receiver

  
    * Coil (Inductance +reluctance) .
    * Capacitor.
    * Resistor.
    * Mic.
    * ON OFF switch .
    * Transistor .
    * Antenna
    * Loudspeaker
    * IC UM66 ,IC2741 & ICLM386




           Using this circuit, audio musical notes can be generated and heard up to a distance of 10 metres. The circuit can be divided into two parts: IR music transmitter and receiver. The IR music transmitter works off a 9V battery, while the IR music receiver works off regulated 9V to 12V. Fig. 1 shows the circuit of the IR music transmitter. It uses popular melody generator IC UM66 (IC1) that can continuously generate musical tones. The output of IC1 is fed to the IR driver stage (built across the transistors T1 and T2) to get the maximum range.
Here the red LED (LED1) flickers according to the musical tones generated by UM66 IC, indicating modulation. IR LED2 and LED3 are infrared transmitting LEDs. For maximum sound transmission these should be oriented towards IR phototransistor L14F1 (T3). The IR music receiver uses popular op-amp IC μA741 and audio-frequency amplifier IC LM386 along with phototransistor L14F1 and some discrete components (Fig. 2). The melody generated by IC UM66 is transmitted through IR LEDs, received by phototransistor T3 and fed to pin 2 of IC μA741 (IC2). Its gain can be varied using potmeter VR1. The output of IC μA741 is fed to IC LM386 (IC3) via capacitor C5 and potmeter VR2. The melody produced is heard through the receiver’s loudspeaker. Potmeter VR2 is used to control the volume of loudspeaker LS1 (8-ohm, 1W).
Switching off the power supply stops melody generation. 

Color Sensor

Color sensor is an interesting project for hobbyists. The circuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The circuit is based on the fundamentals of optics and digital electronics.
The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered. The circuit makes use of only ‘AND’ gates and ‘NOT’ gates. When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through.


But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is. Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corresponding to the mixed colour will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which colour it is.
When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully
noted:

1. Potmeters VR1, VR2 and VR3 may be used to adjust the sensitivity of the LDRs.

2. Common ends of the LDRs should be connected to positive supply.

3. Use good quality light filters. The LDR is mounded in a tube, behind a lens, and aimed at the object.
The coloured glass filter should be fixed in front of the LDR as shown in the figure. Make three of that kind and fix them in a suitable case. Adjustments are critical and the gadget performance would depend upon its proper fabrication and use of correct filters as well as light conditions