Wednesday, January 28, 2015

Photo diode

Photo diode is used to capture reflected light of IR LED.
A semiconductor diode that, when exposed to light, generates a potential difference or changes its electrical resistance.

A Photo diode is a reverse biased silicon or germanium pn junction in which reverse current increases when the junction is exposed to light.
When no light is incident on the pn junction of photo diode, the reverse current is extremely small. This is called DARK CURRENT.

When light is incident on the pn junction of the photo diode there is a transfer of energy from the incident light (photons) to the atoms in the junction .this will create more free electrons (and more holes) these additional free electrons will increase the reversecurrent.This electrical energy can be recorded as voltage drop fluctuations by using a series resistor in the outer circuit and taking voltage readings across it.


An Infrared light-emitting diode (IR LED) is a type of electronic device that emits infrared light not visible to the naked eye.

The wavelength and colour of the light produced depend on the material used in the diode. Infrared LEDs use material that produces light in the infrared part of the spectrum, that is, just below what the human eye can see. Different infrared LEDs may produce
infrared light of differing wavelengths, just like different LEDs produce light of different colours.
Since the human eye cannot see the infrared radiations, it is not possible for a person to identify whether the IR LED is working or not, unlike a common LED. To overcome this problem, the camera on a cell phone can be used. The camera can show us the IR rays being emanated from the IR LED in a circuit.

Monday, January 5, 2015

Voice Control System for Smart Home using Zigbee Technology

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By using Zigbee home automation, we can provide support systems for the elderly and the disabled and who live alone. It recognizes the voice commands and uses low-power RF ZigBee wireless communication modules which are relatively cheap. This system is intended to control all lights and electrical appliances in a home or office using voice commands.

Thursday, January 1, 2015

How to Test LED using Digital Multimeter

Light emitting diode (LED)is a small component used in almost every electronic device. Led has 2 terminals or legs. The bigger leg is the anode or positive terminal and shorter leg is cathode or negative terminal.
But this method of identifying the leads will not always work. Consider the case in which the legs of the LEDs are already cut into same lengthfor using in a circuit. Even in such cases the following method works.
Just take a close look at the geometry of a standard 5mm LED.
The one side is rounded shape and the other side has been made a little straighter (right hand side drawing in the image). The leg in the straight side is always negative and the leg in the rounded side is always positive.

Set the digital multimeter on the continuity mode. If you touch the testing leads to each other the multimeter will give a continuous beep sound. The beep sound means that the multimeter is working perfectly.
In the above multimeter, the knob is turned to the continuity mode which is at 400 ohm section. Testing leads should be plugged into the multimeter as shown in the above image.
probes are connected to the LED terminal according to their polarity. Longer leg is connected to the positive supply and shorter to negative (grounded).

Checking the continuity
Power ON the multimeter
Set the knob on the continuity mode.
LED will glow indicating that it is in working condition
If the LED doesn’t glows then check the connections else the LED is faulty.


Wishing U all a very happy new year 2015.