Does the Logic Sensor (Night) Activate Again When Day Comes
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Mr. Mainak Maji is student of Electrical Engineering from College of Engineering and Management, Kolaghat, India
Automated dark light control organization needs no manual operation for switching ON and OFF when in that location is need of calorie-free. Information technology detects itself whether there is need for light or not. When darkness rises to a sure value then automatically light is switched ON and when there is other source of light i.e. day fourth dimension, the light gets OFF.
In the project we employ light detecting resistor as a light sensor & a NAND gate for detection of high level or low level of voltage to energize the RELAY gyre which is used to interface the control circuit with the external light source.
Wastage of ability is not desirable in any system. And then it is very much economic to have this system and then that power is non wasted during day fourth dimension where manual operation is not possible. Though nosotros can use information technology in our daily life also for the betterment of our arrangement.
While dealing with this project we faced a problem that the lite remained on or off depending upon the presence of whatever other lite source. If we desire to make the light off in dark hours when there is no need of light, or after switching off the light if we want to make the light on again information technology was non possible with the excursion investigated earlier. As we don't want any manual operation we take an arrangement of doing this past means of audio (similar clapping sound).This mechanism makes the circuit is more flexible.
By ways of this circuit we tin can command any other electrical appliances equally nosotros use the double pole double throw relay switch.
Again for economic operation it is very much helpful and it is very much easy and cheap to make the circuit for house concur purposes.
The operation and operating characteristics of the components which are used in the circuits are briefly outlined below-
LDR
LDR s or Lite Dependent Resistors are very useful particularly in light/nighttime sensor circuits. Ordinarily the resistance of an LDR is very high, sometimes equally loftier as 1000 000 ohms, just when they are illuminated with low-cal resistance drops drastically.
The figure above shows that when the torch is turned on, the resistance of the LDR falls,allowing current to pass through information technology.
When a light level of thou lux (bright low-cal) is directed towards it, the resistance is 400 (ohms).
When a light level of ten lux (very low low-cal level) is directed towards it, the resistance has
risen dramatically to x.43M (10430000 ohms).
Ability Supply
For 12v power supply we take used 12 v step downwards transformer, bridge rectifier, 12 regulator.
Transistor
Transistors are usually used as electronic switches, for both high power applications including switched-mode power supplies and low power applications such equally logic gateS
In a grounded-emitter transistor circuit, such every bit the light-switch circuit shown, as the base of operations voltage raises the base and collector current ascension exponentially, and the collector voltage drops considering of the collector load resistor. The relevant equations:
FiveRC = ICE × RC, the voltage across the load (the lamp with resistance RC)
VRC + VCE = 5CC, the supply voltage shown every bit 6V
If VCE could fall to 0 (perfect closed switch) then Ic could become no college than VCC / RC, even with higher base voltage and current. The transistor is so said to be saturated. Hence, values of input voltage tin be chosen such that the output is either completely off, or completely on. The transistor is interim every bit a switch, and this blazon of operation is common in digital circuits where merely "on" and "off" values are relevant.
Transistor Amplifier
• How do we apply the transistor as an amplifier?
• Showtime, we must connect it appropriately to the supply voltages,input signal, and load, and so it tin be used
• A useful style of performance is the mutual-emitter configuration.
To brand a practical circuit, we accept to add together bias and load resistors to ensure the transistor is at the desired operating point.
The resistors continued to the base of operations ensure that the Exist junction is frontwards biased. They finer form a potential divider to reduce the voltage supplied to the base.
The emitter resistor work with the base resistors to stabilise the operating signal with respect to variations in B due to component variation and temperature by providing negative feedback.
Finally, the collector resistor provides the load.
Assume Ib is pocket-sized so tin exist neglected.
•Electric current through base resistors is 20/(110+10)=1/6 mA
•Voltage at base of operations =1/6 * 10 =1.7V
•Therefore EB junction is forrard biased
•Voltage at emitter = 1.7-0.7=1.0V
•Electric current Ie = -ane.0mA
•Current Ic = -aIe = -Ie =one.0mA
•Voltage at collector = 20 -1*ten=10V
•Nosotros ordinarily prepare the collector voltage to exist halfway between Vcc and 0V.
A signal, such every bit music from a CD role player, is applied to the input.
• Let'due south examine what happens when such a betoken increases the base voltage by Vin.
• The emitter voltage is always 0.7V beneath Vb, so if Vb changes past Vin , so does Ve.
• Thus the emitter electric current increases past Vin /Re.
• But Ic=-aIe=-Ie, and so it likewise increases by Vin /Re.
• Thus the voltage at the collector will increase by -Vin RL/Re (that is, it will subtract)
• In this case RL/Re is 10, so the circuit amplifies the input voltage signal by a factor of -10.
• In full general, the gain is -RL/Re. The negative sign indicates that a increase in input voltage leads to a decrease in output voltage.
555 Monostable Multivibrator
A monostable excursion produces a single output pulse when triggered. It is called a monostable because information technology is stable in just ane state: 'output low'. The 'output high' country is temporary.
The duration of the pulse is chosen the time period (T) and this is adamant by resistor R1 and capacitor C1:
Time catamenia, T = i.one × R1 × C1
T = fourth dimension menses in seconds (south)
R1 = resistance in ohms
C1 = capacitance in farads (F)
The maximum reliable time catamenia is about ten minutes.
Why 1.ane The capacitor charges to 2/3 = 67% so it is a bit longer than the time constante (R1 × C1) which is the fourth dimension taken to charge to 63%.
Choose C1 first (there are relatively few values available).
- Choose R1 to give the time period you demand. R1 should be in the range 1k to 1M , and so use a fixed resistor of at least 1k in series if R1 is variable.
- Beware that electrolytic capacitor values are not accurate, errors of at least 20% are common.
- Beware that electrolytic capacitors leak accuse which substantially increases the fourth dimension catamenia if you lot are using a loftier value resistor – use the formula every bit merely a very crude guide!
Monostable Operation
The timing period is triggered (started) when the trigger input (555 pivot 2) is less than 1 / 3 Vs, this makes the output loftier (+Vs) and the capacitor C1 starts to charge through resistor R1. Once the time catamenia has started farther trigger pulses are ignored.
The threshold input (555 pin half dozen) monitors the voltage beyond C1 and when this reaches 2 / iii Vs the fourth dimension flow is over and the output becomes low. At the same fourth dimension belch (555 pivot 7) is connected to 0V, discharging the capacitor ready for the side by side trigger.
The reset input (555 pin 4) overrides all other inputs and the timing may be cancelled at any time by connecting reset to 0V, this instantly makes the output low and discharges the capacitor. If the reset function is non required the reset pivot should exist continued to +Vs.
Power-on Reset or Trigger
It may exist useful to ensure that a monostable circuit is reset or triggered automatically when the power supply is connected or switched on. This is achieved by using a capacitor instead of (or in addition to) a push switch as shown in the diagram.
The capacitor takes a brusque time to charge, briefly holding the input close to 0V when the circuit is switched on. A switch may exist continued in parallel with the capacitor if transmission performance is also required.
Edge-triggering
If the trigger input is still less than one/3 Vs at the stop of the time period the output will remain high until the trigger is greater than 1/3 Vs. This situation tin can occur if the input point is from an on-off switch or sensor.
The monostable tin be made edge triggered, responding only to changes of an input point, by connecting the trigger signal through a capacitor to the trigger input. The capacitor passes sudden changes (Ac) but blocks a constant (DC) betoken. For further information please encounter the page on capacitance . The circuit is 'negative edge triggered' considering it responds to a sudden autumn in the input signal.
The resistor betwixt the trigger (555 pivot 2) and +Vs ensures that the trigger is commonly high (+Vs).
Flip Flop
Some other variation on a theme of bistable multivibrators is the J-K flip-flop. Essentially, this is a modified version of an S-R flip-flop with no "invalid" or "illegal" output state. Look closely at the following diagram to see how this is accomplished:
What used to be the S and R inputs are now chosen the J and K inputs, respectively. The old two-input AND gates have been replaced with three-input AND gates, and the tertiary input of each gate receives feedback from the Q and not-Q outputs. What this does for u.s. is permit the J input to accept outcome only when the circuit is reset, and permit the Thousand input to accept effect just when the circuit is fix. In other words, the ii inputs are interlocked, to use a relay logic term, and then that they cannot both be activated simultaneously. If the circuit is "ready," the J input is inhibited by the 0 status of not-Q through the lower AND gate; if the excursion is "reset," the K input is inhibited past the 0 status of Q through the upper AND gate.
When both J and Chiliad inputs are 1, however, something unique happens. Because of the selective inhibiting action of those 3-input AND gates, a "set" state inhibits input J so that the flip-flop acts every bit if J=0 while K=i when in fact both are 1. On the next clock pulse, the outputs will switch ("toggle") from set (Q=ane and not-Q=0) to reset (Q=0 and not-Q=1). Conversely, a "reset" state inhibits input Yard so that the flip-flop acts equally if J=1 and Chiliad=0 when in fact both are 1. The next clock pulse toggles the circuit once again from reset to set.
The end result is that the S-R flip-flop'south "invalid" state is eliminated (along with the race condition it engendered) and we become a useful feature as a bonus: the ability to toggle betwixt the two (bistable) output states with every transition of the clock input signal.
At that place is no such matter as a J-Chiliad latch, simply J-K flip-flops. Without the edge-triggering of the clock input, the circuit would continuously toggle between its ii output states when both J and K were held high (ane), making it an astable device instead of a bistable device in that circumstance. If we want to preserve bistable operation for all combinations of input states, we must use edge-triggering and then that it toggles just when we tell it to, one pace (clock pulse) at a time.
The block symbol for a J-Chiliad flip-flop is a whole lot less frightening than its internal circuitry, and just like the S-R and D flip-flops, J-K flip-flops come up in two clock varieties (negative and positive edge-triggered):
Nand Gate
NAND ways Non AND,i.e. the AND output is NOTed.And then,a NAND gate is a combination of an AND gate and a NOT gate. In fact NAND is a contraction of the word Non-AND.
The output is logic 0 level, only when each of the input assumes a logic 1 level. For whatever other combination of inputs, the output is a logic i level.
Truth Tabular array
| INPUT | OUTPUT | |
| A | B | Ten |
| 0 | 0 | i |
| 0 | i | i |
| 1 | 0 | 1 |
| i | 1 | 0 |
A 2 INPUT NAND GATE
Relay
A relay is an electrically operated switch that isolates one electrical circuit from some other. In its simplest form, a relay consists of a coil used as an electromagnet to open and close switches contacts. Since the 2 circuits are isolated, a lower voltage circuit can be used to trip a relay, which will command a split circuit that requires a college voltage or amperage. A 12-volt relay requires 12 volts direct electric current (DC) to energize the roll
Switch contacts on a relay can be in one of two states, normally open (NO) or ordinarily closed (NC). When the coil is at remainder and not energized (no current flowing through it), the switch contacts are given the designation NO or NC. In an open circuit, no current flows, such as a wall light switch in your habitation in the downwardly position when the light is off. In a closed circuit, metal switch contacts touch each other to consummate a circuit, and current flows, similar to flipping up a wall light switch to the "On" position.
How the Circuit Functions?
Using LDR
A single NAND gate, a PNP transistor and few other passive components are the just things needed to construct this useful gadget. The circuit description tin be understood from the following explanation:
As shown in the diagram a single NAND gate N1 from the IC 4093 is configured as an inverter and a voltage monitor.
- A reference voltage can be set at its input with the assist of VR1. This adjustment will set the level of darkness at which the system volition modify state.
- A LDR (Light Dependant Resistor) which is also connected at the input of N1 is used to sense a difference in lite levels. A LDR is in fact a resistor which changes its value with a change in the intensity of light falling on information technology.
- In the absence of calorie-free or when its dark, the LDR offers an infinite resistance and thus the input of N1 is kept at logic high due to the voltage received through VR1. This means that at this instant the output of N1 is logic low, the relay is activated through T1 and the lights (load) connected to the relay contacts are switched ON.
- With an increase in the ambient lite the resistance of the LDR volition gradually autumn and after a certain level the input of N1 will become logic low. Immediately its output will get high switching OFF the transistor, the relay and the lights.
- Capacitor C1 has been kept to avoid the relay from chattering during twilight threshold levels.
LDR & Sound Control
In lodge to make the light off during night nosotros can use the following scheme. For that we take to use some other relay coil. The normally closed contacts are used here simply after the 10k resistance which fed the signal to the BJT, as a switch. Now as the switch is closed the circuit volition function normally. But if we energize the coil of the second relay it will disconnect the circuit and the light will off. Once again if nosotros de-energize the scroll it will make the circuit close and light will glow. We tin simultaneously do the functioning thereafter. A clapping audio is used for the operation of the relay coil.
Theory of Operation
Figure 1 shows the block diagram of the Sound Activated Switch. It consists of a transistor amplifier, a transistor switch and 2 types of digital circuits, a one-shot and a flip-bomb.
The Transistor Amplifier
A waveform is created when hands are clapped together. The MIC senses this waveform and couples it to the base of T2 by capacitor C2 (refer to schematic diagram). The transistor is configured equally a mutual emitter amplifier since the AC signal is bypassed to footing by resistance. The transistor amplifier is set for a proceeds of fifty, and then the waveform is amplified l times. Capacitor C3 couples the amplified waveform to the input of the first digital circuit.
The One-Shot / Monostable Multivibrator
A one-shot, or monostable multivibrator, is a circuit that, once triggered, will switch its output logic level. The output will remain at this new logic level for a predetermined flow of fourth dimension, after which the output will switch back to its previous logic state. This output pulse is so coupled to the input of the flip-flop.
Hither the 555 timer serves equally monostable multivibrator.
The Flip-Flop / Bistable Multivibrator
A flip-flop, or a bistable multivibrator, is a circuit whose output logic level changes when a pulse is applied to the input. The output will remain at its logic state until the next pulse is applied. The merely 2 possible output states for a flip-flop are logic 1 and logic 0.
Here nosotros employ IC 4027 (J Thou flip-flop) to make bistable multivibrator.
The Relay Switch
Equally explained earlier the relay volition operate as a switch. The relay volition be connected in normally ON position. Every bit per the clapping sound the amplifier will dilate information technology and monostable multivibrator gives a shot to the flip-flop to energize the relay scroll. As a result the connection volition proceed to normally OFF position. So the light will be in OFF condition until another clapping sound volition make the flip-flop into off state. Every bit a result the light will glow once again.
Pivot Diagram of IC's Used
Implementation
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The entire excursion of this 12 volt 24-hour interval night switch can be built over a minor piece of full general PCB and the whole assembly along with the transformer may be housed inside a expert looking ABS plastic enclosure. Only the LDR has to exist stock-still over the box so that it tin can sense the ambience daylight.
Have due care to position the LDR in such way that no other devious light or the light which it's decision-making is able to be incident on it, or else information technology may produce false switching and may start oscillating. The best position would exist to install the unit at a betoken much college than the lights which are controlled by it.
This automatic night light organisation may also be appropriately used to control building porch lights, neon signs, big advertising displays, gallery lights and also every bit automatic house interior decorative lights. Thus this simple inexpensive circuit should not just be able to relieve you from the headache of timely switching the item lights but as well will result in quite an economical mode of using them.
A Suggested Modification
Later on making it off in the nighttime by means of clapping noise, the light remains in off state though some other night comes in the very next twenty-four hour period. To
brand the light on we have to brand another clapping noise. This is a difficulty of our excursion. Normally our circuit performs at the start when it is
set to low level. So to brand the perform correctly we have to ready it to a low level at each time of start of the operation. In this way the trouble
may be eradicated.
Discussion
We faced problem while energizing the relay scroll. A voltage almost equal to 12 V was required to switch the position from normally ON to normally OFF position of the relay.Simply using i LDR it is not sufficient to vary the voltage betwixt 7 Five and 12 V.So, we use ii LDR in order to accept sufficient voltage driblet. In the circuit nosotros utilise 12V for the performance of BJT.In order to friction match this voltage level a NAND gate , whose operating voltage is 12V, was chosen.
Conclusion
We all know the importance of saving electrical power. Just ironically at times we find the street lights ON even during twenty-four hour period time. This clearly shows how irresponsible one tin be. So instead of depending on individu als, why not take the assistance of electronics and find a solution to get the piece of work done automatically? A elementary circuit of an automatic night low-cal described in this article tin can very accurately switch ON a load (street lights for example) when darkness falls and switch it OFF when dawn breaks.
Circuit Diagrams
Filed Nether: Electronic Projects
Source: https://www.engineersgarage.com/automatic-night-light-control/
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