Showing posts with label Night. Show all posts
Showing posts with label Night. Show all posts
Thursday, 2 March 2017
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.
Wednesday, 18 January 2017
Automatic Night Light using LDR
Here is the simple Automatic Night Light circuit using LDR.
Components Required:
1) Breadboard
2) 470 ohm resistor
3) 22 Kilo ohm resistor
3) 22 Kilo ohm resistor
4) LED (Any Color)
5) 15 Kilo ohm Light Dependent Resistor (LDR)
6) 3904 NPN Transistor
5) 15 Kilo ohm Light Dependent Resistor (LDR)
6) 3904 NPN Transistor
6) 9Volt Battery
Procedure:
Procedure:
- Connect the circuit as shown in the circuit diagram below.
- During day time the brightness will be more, which lowers the resistance of the LDR.
- Therefore the current is grounded, as current prefers only low resistance path.
- Hence there is no base current to forward bias the 3904 NPN transistor and the LED remains OFF.
- During night time the brightness goes down, which increases the resistance of the LDR.
- Therefore the current will not be grounded and prefers a alternate path to flow.
- Hence there is enough base current to forward bias the 3904 NPN Transistor and the LED glows.
Circuit Diagram:
Figure 1: Automatic Night Light using LDR Circuit simulation made in Multisim
Figure 1: Automatic Night Light using LDR Circuit simulation made in Multisim
Figure 2: Automatic Night Light using LDR
USB LED Night Light Circuit Diagram
A typical USB LED bulb shown in Fig. 1 is a 5V, 5W USB-powered solid-state lamp. At the heart of this light bulb is a circular aluminium PCB made with a bunch of 5730 SMD super-bright LEDs. Typical working voltage of a single 5730 SMD LED is in the range of 2.9V to 3.4V, and its current consumption is about 150mA. Fig. 2 shows some details of SMD LEDs used in the USB LED bulb.
This gizmo inspired me to design a distinct USB LED night light with battery backup. Read More Click He
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