Submitted By:

Mahalunkar Abhijit S ……….…………..060401Noah Dionisio Silveira…………………...060422Nikhil Rajiv Kakodkar…..…………………060443

INDEX: Page no.

1. Objective..……………………………………………………………………………………………………3

2. Circuit Diagram………………………………………………………….………………………………..4

3. Operation…………………………………………………………………………………………………….5

4. Component List with Respective Prices……………………………………….……………6

5. Appendix……………………………………………………………………………………………………….7

2

7. References…………………………………………………………………………………………………...12

Objective:

The main motive behind the building of this project:

• To design an effective Security System with minimal Budget.

• By Utilizing this Device, one can check for intruders on site, within a specific range.

• The designed device is affordable to the consumers.

3

CIRCUIT DIAGRAM:

LIGHT FENCE

4

Operation:

The circuit described here is so sensitive that it will detect a moving person at a distance of few metres in daylight or under electric lighting without cumbersome alignment of light beam. It requires virtually no set up, and may be simply placed within the line-of-sight of almost any light source including ambient day light or fluorescent electric light. The beep generated from the circuit will be loud enough to detect the entry of a person in the room or the protected area being guarded. The circuit uses a voltage comparator and a monostable timer to give the warning alarm on detecting a moving person. IC μA741 (IC1) is used as a voltage comparator with two potential dividers in its inverting and non inverting inputs. Resistors R1 and R2 provide half-supply voltage of 4.5 volts to its inverting input (pin 2). LDR1 and preset VR1 form another potential divider to provide a variable voltage input to the non-inverting input(pin 3). If VR1 is properly adjusted for the required light level, the output of IC1 will be high, which drives pnp transistorT1 out of conduction. This is due to the high potential at the base of T1. The emitter voltage of T1 will be high in this condition, which inhibits IC2 from oscillation and LED1 from

5

lighting. IC2 is wired as a monostable timer. R6 and C2 provide a preset time delay.As a person crosses the protected area, his shadow will be sensed by LDR1 due to change in the light intensity level and the voltage at the non-inverting input of IC1 will drop momentarily. The output of IC1 suddenly becomes low, allowing T1 to conduct. This triggers the monostable (IC2) and the alarm sounds. Assemble the circuit on a common PCB and house in a plastic case. Keep LDR1 inside a black tube to increase its sensitivity.Adjust preset VR1 until LED1 turns off at the particular light level. Keep LDR1 facing the entrance of the room or the area to be protected. Sensitivity of the circuit depends on the proper adjustment of VR1. If VR1 is correctly adjusted, the circuit can detect a moving person from a distance of about three metres. _COMPONENT LIST & RESPECTIVE PRICES:

Components Qty. Price (Rs.)

IC:NE555 1 10Μa741 1 15

Capacitors:0.01μF 1 11μF 1 1

Transistor:BC557(pnp) 1 3

6

Resistors:10kΩ 2 0.5*2=11kΩ 2 0.5*2=1470Ω 1 0.5

Potentiometers:0Ω-47kΩ pot 1 100Ω-1MΩ pot 1 15

Other:Tack board 1 10Piezo Buzzer 1 25LDR 1 10LED 1 1

Grand Total: 103.5APPENDIX:1) IC μA741

DESCRIPTION:The μA741 is a general-purpose operational amplifier featuring offset-voltage null capability.The high common-mode input voltage range and the absence of latch-up make

the amplifier ideal for voltage-follower applications. The device is short-circuit protected and the

7

internal frequency compensation ensures stability without external components. A low value potentiometer may be connected between the offset null inputs to null out the offset voltage as shown in Figure 2. The μA741C is characterized for operation from 0°C to 70°C. The mA741I is characterized for operation from –40°C to 85°C.The μA741M is characterized for operation over the full military temperature range of –55°C to 125°C.

8

9

2) IC-NE555 Monostable

DESCRIPTION:The 555 monolithic timing circuit is a highly stable controller capable of producing accurate time delays, or oscillation. In the time delay mode of operation, the time is

precisely controlled by one external resistor and capacitor. For a stable operation as an oscillator, the free running frequency and the duty cycle are both accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output structure can source or sink up to 200 mA.FEATURES• Turn-off time less than 2 ms• Max. operating frequency greater than 500 kHz• Timing from microseconds to hours• Operates in both astable and monostable modes• High output current

10

• Adjustable duty cycle• TTL compatible• Temperature stability of 0.005% per °CAPPLICATIONS• Precision timing• Pulse generation• Sequential timing• Time delay generation• Pulse width modulation

11

12

Trigger Pulse Width Requirements and Time Delays

Due to the nature of the trigger circuitry, the timer will trigger on the negative going edge of the input pulse. For the device to time out properly, it is necessary that the trigger voltage level be returned to some voltage greater than one third of the supply before the time out period. This can be achieved by making either the trigger pulse sufficiently short or by AC coupling into the trigger. By AC coupling the trigger, see Figure 6, a short negative going pulse is achieved when the trigger signal goes to ground. AC coupling is most frequently used in conjunction with a switch or a signal that goes to ground which initiates the timing cycle. Should the trigger be held low, without AC coupling, for a longer duration than the timing cycle the output will remain in a high state for the duration of the low trigger signal, without regard to the threshold comparator state. This is due to the predominance of Q15 on the base of Q16, controlling the state of the bi-stable flip-flop. When the trigger signal then returns to a high level, the output will fall immediately. Thus, the output signal will follow the trigger signal in this case. Another consideration is the “turn-off time”. This is the measurement of the amount of time required after the threshold reaches 2/3 VCC to turn the output low. To explain further, Q1 at the threshold input turns on after reaching 2/3 VCC, which then turns on Q5, which turns on Q6. Current

13

from Q6 turns on Q16 which turns Q17 off. This allows current from Q19 to turn on Q20 and Q24 to given an output low. These steps cause the 2 ms max. delay as stated in the data sheet.Also, a delay comparable to the turn-off time is the trigger release time. When the trigger is low, Q10 is on and turns on Q11 which turns on Q15. Q15 turns off Q16 and allows Q17 to turn on. This turns off current to Q20 and Q24, which results in output high. When the trigger is released, Q10 and Q11 shut off, Q15 turns off, Q16 turns on and the circuit then follows the same path and time delay explained as “turn off time”. This trigger release time is very important in designing the trigger pulse width so as not to interfere with the output signal as explained previously.

REFERENCES & ACKNOWLEDGEMENTS:

The idea of the project was taken from •EFY (Electronics For You), which posed as a big help in getting the components and the directions for doing this project, Besides this, we utilized the net as an aid in helping us understand the working of the various components we used in building this project. We give credit even to the individuals who we might not even know, who rendered us this information by uploading their knowledge onto the site, Below are the sites visited to

14

obtain the Data Sheets as well as info on the various components:1) www.efymag.com 2) www.datasheetcatalog.com 3) www.kpsec.freeuk.com 4) www.basicelec.com And I would not like 2 forget the search engines that made it possible for us to filter down from massive web servers, the data we actually wanted.

Our GEC Library helped us in obtaining the apt information for understanding the functioning of the components, below are the books used:1) Op-Amps and Linear Integrated circuit –

Ramakant Gayakwad

Now last but not the least, I would like to thank our ever inspiring professors who motivated us to do the project, thus strengthening our basics, as well as expanding our knowledge to the practical applications of the components, which we study everyday during our lectures.

1) Mr. Samarth Borkar2) Mr. Shahjahan Kutty

15