Automatic Light Switch | Electronic Project Circuits

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Automatic Light Controller Using 7806

Voltage regulator ICs (78xx series) provide a steady output voltage, as against a widely fluctuating input supply, when the common terminal is grounded. Any voltage about zero volt (ground) connected in the common terminal is added to the output voltage. That means the increase in the common terminal voltage is reflected at the output. On the other hand, if the common terminal is disconnected from the ground, the full input voltage is available at the output. This characteristic is utilised in the present circuit.
When the common terminal is connected to the ground,the regulator output is equivalent to the rated voltage, and as soon as the terminal is disconnected from the ground, the output increases up to the input voltage. The common terminal is controlled by a transistor, which works as a switch on the terminal. For automatic control of light, a light-dependent resistor (LDR1) is connected to the base of the transistor. In this way, the voltage regulator is able to operate a light bulb automatically as per the ambient light. [...]
Author: M.K Chandra – Copyright: EFY Mag
Source:http://www.extremecircuits.net/2010/05/automatic-light-controller-using-7806.html

Be the first to comment - What do you think? Posted by admin - May 4, 2011 at 8:36 am

Categories: Electronic Control, Lighting Tags: Automatic light switch, light control system

Fully Automatic Emergency Light

This simple automatic emergency light has the following advantages over conventional emergency lights:

1. The charging circuit stops automatically when the battery is fully charged. So you can leave the emergency light connected to AC mains overnight without any fear.
2. Emergency light automatically turns on when mains fails. So you don’t need a torch to locate it.
3. When mains power is available, emergency light automatically turns off.

The circuit can be divided into inverter and charger sections. The inverter section is built around timer NE555, while the charger section is built around 3-terminal adjustable regulator LM317. In the inverter section, NE555 is wired as an astable multivibrator that produces a 15kHz squarewave. Output pin 3 of IC 555 is connected to the Darlington pair formed by transistors SL100 (T1) and 2N3055 (T2) via resistor R4.

The Darlington pair drives ferrite transformer X1 to light up the tubelight. For fabricating inverter transformer X1, use two EE ferrite cores (of 25×13×8mm size each) along with plastic former. Wind 10 turns of 22 SWG on primary and 500 turns of 34 SWG wire on secondary using some insulation between the primary and secondary. To connect the tube-light to ferrite transformer X1, first short both terminals of each side of the tube-light and then connect to the secondary of X1. (You can also use a Darlington pair of transistors BC547 and 2N6292 for a 6W tube-light with the same transformer.)
When mains power is available, reset pin 4 of IC 555 is grounded via transistor T4. Thus, IC1 (NE555) does not produce square-wave and emergency light turns off in the presence of mains supply. When mains fails, transistor T4 does not conduct and reset pin 4 gets positive supply though resistor R3. IC1(NE555) starts producing square wave and tube-light turns on via ferrite transformer X1. In the charger section, input AC mains is stepped down by transformer X2 to deliver 9V-0-9V AC at 500mA. Diodes D1 and D2 rectify the output of the transformer. Capacitors C3 and C4 act as filters to eliminate ripples.

The unregulated DC voltage is fed to IC LM317 (IC2). By adjusting preset VR1, the output voltage can be adjusted to deliver the charging voltage. When the battery gets charged above 6.8V, zener diode ZD1 conducts and regulator IC2 stops delivering the charging voltage. Assemble the circuit on a general-purpose PCB and enclose in a cabinet with enough space for the battery and switches. Connect a 230V AC power plug to feed charging voltage to the battery and make a 20W tube outlet in the cabinet to switch on the tube-light.

Source: EFY Mag
Read more : http://www.extremecircuits.net/2010/05/fully-automatic-emergency-light.html

Be the first to comment - What do you think? Posted by admin - February 18, 2011 at 9:14 pm

Categories: Alarm systems, Lighting Tags: automatic control circuit, Automatic light switch, Emergency Light

Midnight Security Light Circuit Schematic

Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical’ sleep. Here is an energy-saving circuit that causes the thieves to abort the theft attempt by lighting up the possible sites of intrusion (such as kitchen or backyard of your house) at around 1:00 am. It automatically resets in the morning. The circuit is fully automatic and uses a CMOS IC CD4060 to get the desired time delay. Light-dependent resistor LDR1 controls reset pin 12 of IC1 for its automatic action. During day time, the low resistance of LDR1 makes pin 12 of IC1 ‘high,’ so it doesn’t oscillate.

After sunset, the high resistance of LDR1 makes pin 12 of IC1 ‘low’ and it starts oscillating, which is indicated by the fashing of LED2 connected to pin 7 of IC1. The values of oscillator components (resistors R1 and R2 and capacitor C4) are chosen such that output pin 3 of IC1 goes ‘high’ after seven hours, i.e., around 1 am. This high output drives triac 1 (BT136) through D5 and R3. Bulb L1 connected between the phase line and M2 terminal of triac 1 turns on when the gate of triac 1 gets the trigger voltage from pin 3 of IC1. It remains ‘on’ until pin 12 of IC1 becomes high again in the morning. Capacitors C1 and C3 act as power reserves, so IC1 keeps oscillating even if there is power interruption for a few seconds. Capacitor C2 keeps trigger pin 12 of IC1 high during day time, so slight changes in light intensity don’t affect the circuit.

Using preset P1 you can adjust the sensitivity of LDR1. Power supply to the circuit is derived from a step-down transformer T1 (230V AC primary to 0-9V, 300mA secondary), rectifed by a full-wave rectifer comprising diodes D1 through D4 and fltered by capacitor C1. Assemble the circuit on a general-purpose PCB with adequate spacing between the components. Sleeve the exposed leads of the components. Using switch S1 you can turn on the lamp manually. Enclose the unit in a plastic case and mount at a location that allows adequate daylight.

Parts:
P1 = 100K
R1 = 120K
R2 = 1M
R3 = 100R
R4 = 100R
C1 = 1000uF-25V
C2 = 100uF-25v
C3 = 100nF-63V
C4 = 1uF-25V
D1 = 1N4001
D2 = 1N4001
D3 = 1N4001
D4 = 1N4001
D5 = Red LED
D6 = Green LED
IC = CD4060
TR = BT136
T1 = 9v 300mA Transformer
L1 = 230V-60W Bulb
SW = On/Off Switch