Automatic Night Light Feeds Directly From the AC Line

There are many approaches to the problem of activating a light when it becomes dark, and a recent Design Idea covers this topic (Reference 1). Some approaches require a dc power supply and an electromechanical relay, but a better approach involves feeding the device directly from the ac line, minimizing the number of components 

(Figure 1).

Figure 1. The photoresistor activates the TRIAC and the load when darkness falls.

The heart of the device is a light-sensitive cadmium-sulphide resistor, PR, with a resistance of approximately 200 kΩ in the dark and decreasing to a few kilohms in the light. PR and capacitor C1 form an ac-voltage divider. In daylight, the voltage across PR is too low to generate the required gate-trigger current to turn on bidirectional ac switch Q1, thus keeping the load – usually a lamp – off. When it becomes dark, PR’s resistance rises, resulting in an increase in the TRIAC’s gate current that triggers the TRIAC and lights the lamp.

The schema uses inexpensive, off-the-shelf components, including the VT90N1 photoresistor; a 0.1-μF, 275V capacitor; and an L2004F61 TRIAC with a load current of 4A rms, a peak blocking voltage of 200V, and a gate-trigger current of 5 mA. The exact specifications of these components are not critical; you could use others instead.

Editor’s note:
Attributes worth mentioning include the fact that the capacitor introduces a phase shift, which places the peak of the gate voltage close to the zero crossing of the load’s sine wave for optimum turn-on timing. Another benefit is thermal hysteresis, which occurs due to the reduction of the required triggering voltage and current as the TRIAC warms up after the initial turn-on. 

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Emergency Light

The schema of automatic emergency light presented here has the following features: 1. When the mains supply (230V AC) is available, it charges a 12V battery up to 13.5V and then the battery is disconnected from the charging section. 2. When the battery discharges up to 10.2V, it is disconnected from the load and the charging process is resumed. 3. If the mains voltage is available and there is darkness in the room, load (bulb or tube) is turned on by taking power from the mains; otherwise the battery is connected to the load. 4. When the battery discharges up to 10.2V and if the mains is not yet available, the battery is completely disconnected from the schema to avoid its further discharge. The mains supply of 230V AC is stepped down to 18V AC (RMS) using a 230V AC primary to 0-18V AC, 2A secondary transformer (X1), generally used in 36cm B&W TVs. Diodes D1 through D4 form bridge rectifier and capacitor C5 filters the voltage, providing about 25V DC at the output. Charging section includes 33-ohm, 10-watt resistor R2 which limits the charging current to about 425 mA when battery voltage is about 10.2V, or to 325 mA when battery voltage is about 13.5V. When the battery charges to 13.5V (as set by VR2), zener diode D17 goes into breakdown region, thereby triggering triac TR1. Now, since DC is passing through the triac, it remains continuously ‘on’ even if the gate current is reduced to zero (by disconnecting the gate terminal). Once the battery is fully charged, charging section is cut-off from the battery due to energisation of relay RL2. This relay remains ‘on’ even if the power fails because of connection to the battery via diode D10. S4, a normally closed switch, is included to manually restart the charging process if required. Battery disconnect and charging restart section comprises an NE555 timer (IC2) wired in monostable mode. When the battery voltage is above 10.2V (as indicated by red LED D15), zener diode (D16) remains in the breakdown region, making the trigger pin 2 of IC2 high, thereby maintaining output pin 3 in low voltage state. Thus, relay RL3 is ‘on’ and relay RL4 is ‘off.’ But as soon as the battery voltage falls to about 10.2V (as set by preset VR1), zener diode D16 comes out of conduction, making pin 2 low and pin 3 high to turn ‘on’ relay RL4 and orange LED D13. This also switches off relay RL3 and LED D15. Now, if the mains is available, charging restarts due to de-energisation of relay RL2 because when relay RL4 is ‘on,’ it breaks the schema of relay RL2 and triac TR1. But if the mains supply is not present, both relays RL3 and RL1 de-energise, disconnecting the battery from the remaining schema. Thus when battery voltage falls to 10.2 volts, its further discharge is eliminated. But as soon as the mains supply resumes, it energises relay RL1, thereby connecting the battery again to the schema. Light sensor section also makes use of a 555 timer IC in the monostable mode. As long as normal light is falling on LDR1, its resistance is comparatively low. As a result pin 2 of IC3 is held near Vcc and its output at pin 3 is at low level. In darkness, LDR resistance is very high, which causes pin 2 of IC3 to fall to near ground potential and thus trigger it. As a consequence, output pin 3 goes high during the monostable pulse period, forward biasing transistor T3 which goes into saturation, energising relay RL5. With auto/bypass switch S2 off (in auto mode), the load gets connected to supply via switch S3. If desired, the load may be switched during the day-time by flipping switch S2 to ‘on’ position (manual). Preset VR3 is the sensitivity control used for setting threshold light level at which the load is to be automatically switched on/off. Capacitors with the relays ensure that there is no chattering of the relays. When the mains is present, diode D8 couples the input voltage to regulator IC1 whereas diode D10 feeds the input voltage to it (from battery) in absense of mains supply. Diode D5 connects the load to the power supply section via resistor R5 when mains is available (diode D18 does not conduct). However, when mains power fails, the situation reverses and diode D18 conducts while diode D5 does not conduct. . The load can be any bulb of 12 volts with a maximum current rating of 2 amperes (24 watts). Resistor R5 is supposed to drop approximately 12 volts when the load current flows through it during mains availability . Hence power dissipated in it would almost be equal to the load power. It is therefore desirable to replace R5 with a bulb of similar voltage and wattage as the load so that during mains availability we have more (double) light than when the load is fed from the battery. For setting presets VR1 and VR2, just take out (desolder one end) diodes D7, D10 and D18. Connect a variable source of power supply in place of battery. Set preset VR1 so that battery-high LED D15 is just off at 10.2V of the variable source. Increase the potential of the variable source and observe the shift from LO BAT LED D13 to D15. Now make the voltage of the source 13.5V and set preset VR2 so that relay RL2 just energises. Then decrease the voltage slowly and observe that relay RL2 does not de-energise above 10.2V. At 10.2V, LED D15 should be off and relay RL2 should de-energise while LED D13 should light up. Preset VR3 can be adjusted during evening hours so that the load is ‘on’ during the desired light conditions

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Capacitance Operated Battery Powered Light Wiring diagram Schematic

Build a simple Capacitance Operated Battery Powered Light Circuit Diagram. Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. A common form of energy storage device is a parallel-plate capacitor. Touch the plate and the light will go on and constant of the 47 µf capacitor and the 2M remain on for a time determined by the time resistor.

Capacitance Operated Battery Powered Light Circuit Diagram

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How to fix a tube light simply

This post shows how to fix a tube light with its parts correctly.lots of people asked me about this that is why I thought to give you some thing like this.now I think you will be able to solve your problems.





Note

# Be careful when you deal with 230v current.

#kids should not test this schema.

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Emergency Light and Alarm circuit

This is a simple and easy emergency light and alarm schema. This schema is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen.

When power supply is restored, the lamp or the alarm is switched-off. A switch provides a "latch-up" function, in order to extend lamp or alarm operation even when power is restored.

Component parts list:

R1 = 220K
R2 = 470R
R3 = 390R
R4 = 1K5
R5 = 1R
R6 = 10K
R7 = 330K
R8 = 470R
R9 = 100R
C1 = 330nF/400V Polyester Capacitor
C2 = 10µF/63V Electrolytic Capacitor
C3 = 100nF/63V Polyester Capacitor
C4 = 10nF/63V Polyester Capacitor
D1-D5 = 1N4007
D6 = LED Green
D7 = 1N4148
Q1,Q3,Q4 = BC547
Q2,Q5 = BC327
SW1,SW2 = SPST Switches
SW3 = SPDT Switch
LP1 = 2.2V or 2.5V 250-300mA Torch Lamp Bulb
SPKR = 8 Ohm Loudspeaker
B1 = 2.5V Battery (two AA NI-CD rechargeable cells wired in series)
PL1 = Male Mains plug

Circuit Works:
Mains voltage is reduced to about 12V DC at C2s terminals, by means of the reactance of C1 and the diode bridge (D1-D4). This avoids the use of a mains transformer.

Trickle-charging current for the battery B1 is provided by the series resistor R3, D5 and the green LED D6 that also monitors the presence of mains supply and correct battery charging.
Q2 & Q3 form a self-latching pair that start operating when a power outage occurs. In this case, Q1 biasing becomes positive, so this transistor turns on the self latching pair.

If SW3 is set as shown in the schema diagram, the lamp illuminates via SW2, which is normally closed; if set the other way, a square wave audio frequency generator formed by Q4, Q5 and related components is activated, driving the loudspeaker.

If SW1 is left open, when mains supply is restored the lamp or the alarm continue to operate. They can be disabled by opening the main on-off switch SW2.

If SW1 is closed, restoration of the mains power supply terminates lamp or alarm operation, by applying a positive bias to the Base of Q2.

Notes:

• Close SW2 after the schema is plugged.
• Warning! The schema is connected to 230Vac mains, then some parts in the schema board are subjected to lethal potential!. Avoid touching the schema when plugged and enclose it in a plastic box.

Emergency Light and Alarm schema source: http://www.reddiagram.com/Page45.htm

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Light Gate with Counter

The schema described here counts the number of times that an infrared beam is interrupted. It could be used to count the number of people entering a room, for instance, or how often a ball or another object passes through an opening (handy for playing shuffleboard). The heart of the schema consists of you guessed it a light gate! Diode D1 is an IR diode that normally illuminates IR transistor T1. The light falling on T1 causes it to conduct to a certain extent. The resulting voltage on the collector of T1 should be just low enough to prevent the following transistor (T2) from conducting. This voltage can be adjusted within certain limits using P1.

Light Gate with Counter Circuit diagram :

Light Gate with Counter Circuit Diagram

As soon as an object comes between D1 and T1, the light shining on T1 will be partially or fully blocked, causing the IR transistor to conduct less current. As a result, the voltage on its collector will increase, producing a brief rise in the voltage on the base of T2. This will cause T2 to conduct and generate a negative edge at IC1. This negative edge will trigger the monostable multivibrator, which will then hold the output signal on pin 3 ‘high’ for a certain length of time (in this case, one second). Atthis point, two things will occur. First, a buzzer will be energised by the output of IC1 and produce a tone for approximately one second. When the buzzer stops, a negative edge will be applied to the clock input of IC2, causing the counter in IC2 to be incremented by 1. IC2 is conveniently equipped with an internal binary-to-BCD decoder, so its outputs only have to be buffered by IC3 and T3 to allow the state of the counter to be shown on the 7-segment display. Switch S1 can be used to reset the counter to zero. 

If a one-second interval does not suit your wishes, you can modify the values of R3 or C1 to adjust the time. Increasing the value of R3 lengthens the interval, and decreasing it naturally shortens the interval. The same is true of C1. When building the schema, make sure that T1 is well illuminated by the light from D1, while at the same time ensuring that T1 ‘sees’ as little ambient light as possible. This can best be done by fitting T1 in a small tube that is precisely aimed toward D1. The longer the tube, the less ambient light will reach T1. The sensitivity of the schema can be adjusted using P1.

Author : T.Hareendran - Copyright : Elektor

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Garage Light and Security Control Wiring diagram Schematic

Useful for vehicle owners, this gadget automatically turns on indoor/outdoor garage lights and raises an alert when an automobile enters the garage.

Garage Light and Security Control Circuit Diagram

Assume switch S2 is in ‘on’ (closed) state. When power switch S1 is turned on, the complete schema is energised by the 12V DC supply. LED3 lights up to provide power-on indication. Simultaneously, IC3 (CD4017B) is instantly reset by the power-on-reset schema formed by the combination of capacitor C4 and resistor R5, and green LED2 lights up as a standby indicator. As per the physical arrangement, IR rays from IR-LED fall on phototransistor T1 and it conducts to pull up the inputs of NAND gate N1 (used here as an inverter) to logic 1. As a result, the output of gate N2 goes high to make the monostable built around IC2 inactive.

Now, when a vehicle moves through the door, the IR beam is interrupted and the output state of gate N2 changes from high to low state, which triggers the monostable and red LED1 (Rx on) lights up briefly. The output of monostable provides clock pulse to IC3, which changes its output state, with its pin 2 going high and pin 3 going low. As a result, standby indicator green LED2 goes off and relay driver pnp transistor T2 gets forward biased via gate N3 to energise relay RL1. The contacts of relay RL1 can be used to switch indoor and outdoor garage lights.

After parking the vehicle, when the owner moves through the passage to interrupt the light beam once again, the monostable (IC2) is retriggered and the output state of IC3 changes again. This time, the output at pin 2 of IC3 goes low, while the output at its pin 4 goes high. This output resets IC3, after a short delay determined by components R8, C5, and D3. Standby LED2 again lights up.

Before the resetting function, the security system drive schema is activated via gate N4 as follows: During retriggering, both inputs (pins 12 and 13) of gate N4 are at high logic level, taking its output pin 11 low to forward bias pnp transistor T3 via resistor R11. As a result, the SCR (BT169) is triggered via R12 and latched. Now the DC supply is extended to the rest of the schema via the SCR until it is reset by disabling switch S2.

Door switch S3 is N/O type and it opens only when the door is opened. This triggers the regenerative pair of transistors T4 and T5, and relay RL2 is energised (and latched). Contacts of relay RL2 may be connected to an emergency beeper, a high-power signalling device, or an automatic telephone dialer, as desired by the user.

Resistor R7 and capacitor C6 have been deliberately added to delay the switching off of relay RL1. This extends the lamp’s ‘off’ time (for a short duration), allowing the owner to move in while the light is on. The delay can be increased by increasing the value of capacitor C6. (Note. A high-value capacitor will also increase the delay in turning the lights on, which is not desirable.)

This schema costs around Rs 150.

Sourced By: EFY Author Name:  T.K. Hareendran

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Photo Meter Assesses Ambient Light Schematic

Most PN-junction diodes can be used as photodiodes. While not optimized for this application, they do work. When the diode is reverse biased, it will produce a small photovoltaic output as the light level is increased. LEDs are particularly suited for this task because their housings are transparent.

You can construct a simple schema that will assess the condition of ambient lighting and, because many LEDs’ packages are tinted to enhance their emitted color, may even yield a reasonable evaluation of the detected color. The results are not as effective as those obtained using a high-quality optical filter, which typically has narrow bandpass characteristics, but they can be quite acceptable. Though the design described here does not produce the accuracy of designs with laboratory-grade photodetectors and transimpedance amplifiers, it can be quickly assembled and will produce usable results at a low cost.

Three LEDs are used; experimentation will indicate which device has the best sensitivity to which color (Figure 1). The ambient light falling on the LEDs causes some current flow—typically in the range of 10 to 100 nA—through each LED, depending on the applied illumination level. This current flows through the base of a transistor, Q1, and is amplified. Q1’s collector current then splits between potentiometer R4, which acts as a first-stage gain calibration, and the base of Q2.

Photo Meter Assesses Ambient Light Schematic

Q2 provides further amplification and drives the left side of a bridge schema (D1A and D1B). Note that R2/D1 and R3/D2 form a balanced bridge. Q2’s collector current provides a slight imbalance to the bridge. The meter, M, measures this imbalance. R5 adjusts the sensitivity of the meter. Set R4 and R5 such that the meter has an appropriate deflection. R4 is useful for selecting the quiescent point; R5 is useful for adjusting the sensitivity.

Before building the schema, check whether the LEDs can be used as photo sensors. To determine whether a given LED is a good photodiode, check the voltage across the LED using a common digital multimeter set to its most sensitive range—typically 200 mV. Typical output voltage should be approximately 0.3 to 1 mV with typical office illumination.

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Simple Light operated switch Wiring diagram Schematic

This is a Simple light-operated switch schema diagram.This light sensitive schema can operate a relay to switch on lamps or any AC loads when it senses darkness. 

 Simple Light-operated switch Circuit Diagram

 It is ideal to use as switch less night lamps. This schema uses a flip-flop arrangement of Ql and Q2. Normally Ql is conducting heavily. Light on CDS photocell causes Ql bias to decrease, cutting it off, turning on Q2, removing the remaining bias from Q1. Reset is accomplished by depressing S1

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LED light flasher

This is a very basic schema for flashing one or more LEDS and also to alternately flash one or more LEDs.

It uses a 555 timer setup as an astable multivibrator with a variable frequency.
With the preset at its max. the flashing rate of the LED is about 1/2 a second. It can be increased by increasing the value of the capacitor from 10uF to a higher value. For example if it is increased to 22uF the flashing rate becomes 1 second.

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Make a Warning Light and Marker Light Wiring diagram Schematic

Make a Warning-light-and-marker-light. This is a led flasher light, A flashing light of high brightness and short duty cycle is often desired to provide maximum visibility and battery life. This necessitates using an output transistor, which can supply the cold filament surge current of the lamp while maintaining a low saturation voltage. The oscillation period and flash duration are determined in the feedback loop, while the use of a photo transistor sensor minimizes sensitivity variations.

Warning Light and Marker Light Circuit Diagram

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Electronic Light Switch Wiring diagram Schematic

This is a simple Electronic Light Switch Circuit Diagram.. The schema is a light switch who triggers when light drops on photo resistor. It is fairly simple in construction and can be used in a million applications. The photo resistor and the trimmer work as a voltage divider and also polarize the transistor TR1. TR1 triggers TR2 and TR2 drives the relay. Trimmer R7 is for adjusting the sensitivity of the schema. 

 Switching Improves Regulator Efficiency Circuit Diagram

  Electronic Light Switch Circuit Diagram

Parts: 
R = photoresistor
R1= 4.7 Kohm
R2= 1.2 Kohm
R3= 2.2 Kohm
R4= 1.2 Kohm
R5= 1.2 Kohm
R6= 2.7 Kohm
R7= 100Kohm
Trimmer
C1 = 10uf/16V
electrolytic
TR1= BC107 - BC108 NPN
TR2= BC107 - BC108 NPN
TR3= BC557 - BC558 PNP - BC327
D1 = 1N4148 Relay = any 12Volt relay

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Emergency Light and Alarm Wiring diagram Schematic

This is a simple combination of schema. Emergency Light and Alarm Circuit Diagram is permanently plugged into a mains socket andNI-CD batteries are trickle-charged. When a power outage occurs,the lamp automatically illuminates. Instead of illuminating alamp, an alarm sounder can be chosen.When power supply is restored, the lamp or the alarm isswitched-off. A switch provides a “latch-up” function, in orderto extend lamp or alarm operation even when power is restored.Circuit operation:Mains voltage is reduced to about 12V DC at C2`s terminals, bymeans of the reactance of C1 and the diode bridge (D1-D4). Thusavoids the use of a mains transformer.

 Simple Emergency Light and Alarm Circuit Diagram

Trickle-charging current for the battery B1 is provided by theseries resistor R3, D5 and the green LED D6 that also monitorsthe presence of mains supply and correct battery charging.Q2 & Q3 form a self-latching pair that start operatingwhen a power outage occurs. In this case, Q1 biasing becomespositive, so this transistor turns on the self latching pair.

If SW3 is set as shown in the schema diagram, the lampilluminates via SW2, which is normally closed; if set the otherway, a square wave audio frequency generator formed by Q4, Q5 andrelated components is activated, driving the loudspeaker.If SW1 is left open, when mains supply is restored the lamp orthe alarm continue to operate. They can be disabled by openingthe main on-off switch SW2.If SW1 is closed, restoration of the mains supply terminateslamp or alarm operation, by applying a positive bias to the Baseof Q2.

Notes:

Close SW2 after the schema is plugged.Warning! The schema is connected to 220Vac mains, then some parts in the schema board are subjected to lethal potential! avoid touching the schema when plugged and enclose it in a plastic box. 

Parts List
R1____________220K 1/4W Resistor
R2____________470R 1/2W Resistor
R3____________390R 1/4W Resistor
R4______________1K5 1/4W Resistor
R5______________1R 1/4W Resistor
R6_____________10K 1/4W Resistor
R7____________330K 1/4W Resistor
R8____________470R 1/4W Resistor
R9____________100R 1/4W Resistor

C1____________330nF 400V Polyester Capacitor
C2_____________10΅F 63V Electrolytic Capacitor
C3____________100nF 63V Polyester Capacitor
C4_____________10nF 63V Polyester Capacitor

D1-D5________1N4007 1000V 1A Diodes
D6______________LED Green (any shape)
D7___________1N4148 75V 150mA Diode

Q1,Q3,Q4______BC547 45V 100mA NPN Transistors
Q2,Q5_________BC327 45V 800mA PNP Transistors

SW1,SW2________SPST Switches
SW3____________SPDT Switch

LP1____________2.2V or 2.5V 250-300mA Torch Lamp

SPKR___________8 Ohm Loudspeaker

B1_____________2.5V Battery (tw1o AA NI-CD rechargeable cells wired in series)

PL1____________Male Mains plug

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TRIAC Light Dimmer

This little schema can be used to dim lights up to about 350 watts. It uses a simple, standard TRIAC schema that, in my expirience, generates very little heat. Please note that this schema cannot be used with fluorescent lights.

















Parts
R1 50K Pot
R2 15K 1/2W Resistor
C1, C2 0.068 250V Capacitor
L1 Lamp To Be Controlled (up to 350 watts)
L2 Neon Lamp
TR1 40502 TRIAC
MISC Case, Knob, Heatsink For TR1, Wire, Socket For L1




Notes
1. This schema is for 117VAC only. 220 or 240 V will burn up the schema. L1 can be a maximum of 350 watts.
2. The schema must be installed and used in a case. (Well give you 230 v schema recently)

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