Showing posts with label light. Show all posts
Showing posts with label light. Show all posts
Wednesday, October 15, 2014
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 circuit 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.
The circuit 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.
Thursday, September 4, 2014
Build a Phone light Wiring diagram Schematic
This is a simple Phone light Circuit Diagram. In this schema When the phone does ring the triac is triggered into conduction by a signal applied to its gate (G) through a bilateral switch (diac), D2. The triac acts as a switch, conducting only when a signal is present at the gate.
Phone light Circuit Diagram
Monday, September 1, 2014
Ringing phone light flasher
This schema can be used to glow a bulb or turn a alarm when the phone rings.Using this schema nuissence of telephone ring at night can be avoided.
When the telephone rings the line voltage rises to 72 volts.At this time the LED in the opto-coupler glows and the transistor conducts. Due to this the transistor Q1 conducts.This makes the relay ON.The load connected to the relay whether bulb or bell turns ON.
Notes.
* Assemble the schema diagram on a good quality PCB or common board.
* Use a 5V DC power supply for powering the schema.
* The load can be connected through NC1,NC2 & C points of the relay.
Saturday, August 23, 2014
Fire alarm with light sensor
Fire alarm can be made with a light sensor (LDR) as in the article with the title of Fire Alarm with this LDR sensor. Principles of fire detection Fire Alarm with LDR sensor is to detect the presence of smoke through the LDR. LDR in the series Fire Alarm does not stand alone in detecting a fire, but the LDR in the pair with the light shining on the LDR.
Hence, in the detected smoke from the fire then the intensity of light received by the LDR LDR decreases and eventually trigger an alarm system on a series of Fire Alarm with this LDR sensor. Part 2 that in the series of Fire Alarm with Sensor LDR are some of the sensors, tone generator, audio power.
Image Series Fire Alarm with Sensor LDR
Function Section of the Fire Alarm with Sensor LDR
Part of LDR and light sensor facing to fire smoke detection
Part trigger using transistors and regulators as a trigger tone generator 7805
Tone generator section with IC UM66
Power audio section uses an audio power IC TDA 2002 which is equipped with voleme control (R3)
Sunday, August 10, 2014
LIGHT ALARMS
LIGHT ALARM - 1
This schema operates when lightweight|the sunshine} Dependent Resistor receives light. When no lightweight falls on the LDR, its resistance is high and also the transistor driving the speaker isnt turned on. When lightweight falls on the LDR its resistance decreases and also the collector of the second transistor falls. This turns off the primary transistor slightly via the second 100n and also the initial 100n puts a further spike into the bottom of the second transistor. This continues till the second transistor is turned on as onerous because it will go. the primary 100n is currently nearly charged and it cannot keep the second transistor turned on. The second transistor starts to turn off and each transistors swap conditions to provide the second half of the cycle.
This schema operates when lightweight|the sunshine} Dependent Resistor receives light. When no lightweight falls on the LDR, its resistance is high and also the transistor driving the speaker isnt turned on. When lightweight falls on the LDR its resistance decreases and also the collector of the second transistor falls. This turns off the primary transistor slightly via the second 100n and also the initial 100n puts a further spike into the bottom of the second transistor. This continues till the second transistor is turned on as onerous because it will go. the primary 100n is currently nearly charged and it cannot keep the second transistor turned on. The second transistor starts to turn off and each transistors swap conditions to provide the second half of the cycle.
LIGHT ALARM - 2
This schema is comparable to lightweight Alarm -1 however produces a louder output as a result of the speaker being connected directly to the schema. The schema is essentially a high-gain amplifier thats turned on initially by the LDR and then the 10n keeps the schema turning on till it will activate no more. The schema then starts to show off and eventually turns off utterly. the present through the LDR starts the cycle once more.
LIGHT ALARM - 3 (MOVEMENT DETECTOR)
This schema is extremely sensitive and may be placed in a very space to detect the movement of a person up to a pair of metres from the unit.
The schema is essentially a high-gain amplifier (made of the primary 3 transistors) that is turned on by the LDR or photo Darlington transistor. The third transistor charges the 100u via a diode and this delivers turn-on voltage for the oscillator. The LDR has equal sensitivity to the photo transistor during this schema.
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