Automatic Night Lamp with Morning Alarm using 8085 Microprocessor

As the name suggests “Automatic Night Lamp with Morning Alarm” was developed using Microprocessor. 8085 is the Heart of the system. The sensors are made with help of LDR which are Light Dependent Resistors, whose Resistance is inversely proportional to the Light falling on it. The LDR converts the light energy into electrical energy and this variable electrical energy was converted into digital signal (0 or 1) by using the timer IC555. The Timer IC output goes low when light falls on the LDR and the timer IC output goes high when the LDR was placed in dark

circuit is as shown in below figure:

circuit

the flow chart for Automatic Night Lamp with Morning Alarm using 8085 Microprocessor is as shown in following fig.

flow chart

the program for Automatic Night Lamp with Morning Alarm using 8085 Microprocessor this is as shown below make sure that the Power supply pins & Port number before you connect the Hardware to the Trainer Kit.

0001   0000
0002   0000             PORTB EQU 0DH
0003   0000             PORTC EQU 0EH
0004   0000             REG EQU 0FH
0005   0000
0006   0000             .ORG 4100H
0007   4100
0008   4100 3E 82       MVI A,82H ;Set control word for 8255
0009   4102 D3 0F       OUT REG
0010   4104 3E 20       MVI A,00100000B ;switch off LED and alarm
0011   4106 D3 0E       OUT PORTC
0012   4108
0013   4108 DB 0D       UP: IN PORTB
0014   410A FE 20       CPI 20H
0015   410C CA 2F 41     JZ NIGHT ; jump if night
0016   410F 3E 60       MVI A,01100000B ;Switch on music and off light
0017   4111 D3 0E       OUT PORTC ;OUT to port C
0018   4113
0019   4113 0E 14       MVI C,14H ;call delay routine for 10sec
0020   4115 2A FF FF    SEC: LHLD 0FFFFH
0021   4118 3E 09       MVI A,09
0022   411A CD 05 00     CALL 0005
0023   411D 0D           DCR C
0024   411E C2 15 41     JNZ SEC
0025   4121
0026   4121 3E 20       MVI A,00100000B
0027   4123 D3 0E       OUT PORTC
0028   4125
0029   4125 DB 0D       N1: IN PORTB
0030   4127 FE 20       CPI 20H
0031   4129 C2 25 41     JNZ N1
0032   412C C3 08 41     JMP UP
0033   412F
0034   412F 3E 00       NIGHT: MVI A,00H ;switch on LED
0035   4131 D3 0E       OUT PORTC ;
0036   4133 C3 08 41     JMP UP
0037   4136
0038   4136             .END

 no. of errors = 0

FINAL WORDS:
Finally u have learned to make the project Automatic Night Lamp with Morning Alarm using 8085 Microprocessor and make this today and ENJOY.

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difference between earthed and unearthed cables

Introduction:

• In HT electrical distribution, the system can be earthed or unearthed. The selection of earthed/unearthed cable will depend on system. If distribution system is earthed then we have to use cable which is manufactured for earthed system. (Which the manufacturer specifies). If the system is unearthed then we need to use cable which is manufactured for unearthed system. The unearthed system requires high insulation level compared to earthed System.
• For earthed and unearthed XLPE cables, the IS 7098 part2 1985 does not give any difference in specification. The insulation level for cable for unearthed system has to be more.

Earthed System:         

• Earlier the generators and transformers were of small capacities and hence the fault current was less. The star point was solidly grounded. This is called earthed system.
• In Three phases earthed system, phase to earth voltage is 1.732 times less than phase to phase voltage. Therefore voltage stress on cable to armor is 1.732 times less than voltage stress between conductors to conductor.
• Where in unearthed system, (if system neutral is not grounded) phase to ground voltage can be equal to phase to phase voltage. In such case the insulation level of conductor to armor should be equal to insulation level of conductor to conductor.
• In an earthed cable, the three phase of cable are earthed to a ground. Each of the phases of system is grounded to earth. Examples: 1.9/3.3 KV, 3.8/6.6 KV system

 Unearthed System:

• Today generators of 500MVA capacities are used and therefore the fault level has increased. In case of an earth fault, heavy current flows into the fault and this lead to damage of generators and transformers. To reduce the fault current, the star point is connected to earth through a resistance. If an earth fault occurs on one phase, the voltage of the faulty phase with respect to earth appears across the resistance. Therefore, the voltage of the other two healthy phases with respect to earth rises by 1.7 times. If the insulation of these phases is not designed for these increased voltages, they may develop earth fault. This is called unearthed system.
• In an unearth system, the phases are not grounded to earth .As a result of which there are chances of getting shock by personnel who are operating it. Examples : 6.6/6.6 KV, 3.3/3.3 KV system.
• Unearthed cable has more insulation strength as compared to earthed cable. When fault occur phase to ground voltage is √3 time the normal phase to ground voltage. So if we used earthed cable in unearthed System, It may be chances of insulation puncture. So unearthed cable are used. Such type of cable is used in 6.6 KV systems where resistance type earthing is used.

 Nomenclature:

• In simple logic the 11 KV earthed cable is suitable for use in 6.6 KV unearthed system. The process of manufacture of cable is same. The size of cable will depend on current rating and voltage level.
• Voltage Grade (Uo/U) where Uo is Phase to Earth Voltage & U is Phase to Phase Voltage.
• Earthed system has insulation grade of KV / 1.75 x KV.
• For Earthed System (Uo/U): 1.9/3.3 kV, 3.8/6.6 kV, 6.35/11 kV, 12.7/22 kV and 19/33 kV.
• Unearthed system has insulation grade of KV / KV.
• For Unearthed System (Uo/U): 3.3/3.3 kV and 11/11 kV.
• 3 phase 3 wire system has normally Unearthed grade cables and 3 phase 4 wire systems can be used earthed grade cables, insulation used is less, and cost is less.

Thumb Rule:

• As a thumb rule we can say that 6.6KV unearthed cable is equal to 11k earthed cable i.e. 6.6/6.6kv Unearthed cable can be used for 6.6/11kv earthed system. because each core of cable have the insulation level to withstand 6.6kv so between core to core insulation level will be 6.6kv+6.6kv = 11kv
• For transmission of HT, earthed cable will be more economical due to low cost where as unearthed cables are not economical but insulation will be good.
• Generally 6.6 kV and 11kV systems are earthed through a neutral grounding resistor and the shield and armor are also earthed, especially in industrial power distribution applications.  Such a case is similar to an unearthed application but with earthed shield (some times called solid bonding).  In such cases, unearthed cables may be used so that the core insulation will have enough strength but current rating is de-rated to the value of earthed cables. But it is always better to mention the type of system earthing in the cable specification when ordering the cables so that the cable manufacturer will take care of insulation strength and de rating.

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electrical engineering question and answers | interview questions with answers | multiple choice q & a's

 here,

u can get electrical engineering question and answers and multiple choice questions and interview questions part - 1

1)     Why ELCB cannot work if Neutral input of ELCB does not connect to ground?

• ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that same current will have to return neutral so resultant current is zero.
• Once there is a ground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB. That means once side current is going and not returning and hence because of this difference in current ELCB will trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.

2)     What is the difference between MCB & MCCB, Where it can be used?

• MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit.
• Normally it is used where normal current is less than 100A.
• MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. Under voltage and under frequency may be inbuilt.
• Normally it is used where normal current is more than 100A.

3)     Why in a three pin plug the earth pin is thicker and longer than the other pins?

• It depends upon R=ρL/A where area (A) is inversely proportional to resistance (R), so if  area (A) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer because the The First to make the connection and last to disconnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

4)     Why Delta Star Transformers are used for Lighting Loads?

• For lighting loads, neutral conductor is must and hence the secondary must be star winding and this lighting load is always unbalanced in all three phases.
• To minimize the current unbalance in the primary we use delta winding in the primary So delta / star transformer is used for lighting loads.

5)      What are the advantages of star-delta starter with induction motor?

• The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to 3-4 times of current of Direct online starting  Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.

6)     What is meant by regenerative braking?

• When the supply is cut off for a running motor, it still continue running due to inertia. In order to stop it quickly we place a load (resistor) across the armature winding and the motor should have maintained continuous field supply so that back e.m.f voltage is made to apply across the resistor and due to load the motor stops quickly. This type of breaking is called as “Regenerative Breaking”.

7)     When voltage increases then current also increases then why we need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only?

• No. We cannot sense the over voltage by just measuring the current only because the current increases not only for over voltages but also for under voltage (As most of the loads are non-linear in nature).So, the over voltage protection & over current protection are completely different.
• Over voltage relay meant for sensing over voltages & protect the system from insulation break down and firing. Over current relay meant for sensing any internal short circuit, over load condition, earth fault thereby reducing the system failure & risk of fire. So, for a better protection of the system. It should have both over voltage & over current relay.

8)     If one lamp connects between two phases it will glow or not?

• If the voltage between the two phases is equal to the lamp voltage then the lamp will glow.
• When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp.

9)     What are HRC fuses and where it is used?

• HRC stand for “high rupturing capacity” fuse and it is used in distribution system for electrical transformers

10)  Mention the methods for starting an induction motor?

• The different methods of starting an induction motor
• DOL:direct online starter
• Star delta starter
• Auto transformer starter
• Resistance starter
• Series reactor starter

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