Tuesday, July 14, 2015


White Light Emitting Diodes (LED) replaces HID lamps in street lighting system to include dimming feature. A microcontroller of 8051 family is used to control the intensity by developing pulse width modulated signals that drives a MOSFET to switch the LEDs according to achieve desired operation.
In the present system, mostly the lightning up of highways is done through High Intensity Discharge lamps (HID), whose energy consumption is high. Its intensity cannot be controlled according to the requirement so there is a need to switch on to an alternative method of lightning system i.e., by using LEDs. This system is built to overcome the present day drawbacks of HID lamps. This system demonstrates the usage of the LED’s (light emitting diodes) as the light source and its variable intensity control, according to the requirement. LED’s consume less power and its life time is more, as compared to the conventional HID lamps. The more important and interesting feature is its intensity can be controlled according to the requirement during non-peak hours which is not feasible in HID lamps.
A cluster of LEDs are used to form a street light. The microcontroller contains programmable instructions which controls the intensity of lights based on the PWM (Pulse width modulation) signals generated. The intensity of lights are kept high during the peak hours, as the traffic on the roads tend to decrease slowly in the late nights, the intensity also  decreases progressively till morning. Final it completely shuts down at morning 6, and again resumes at 6pm in the evening. The process is repeated.
This concept in future can be enhanced by integrating it with the solar panel, which converts the solar intensity into corresponding voltage, and this energy is used to feed up the highway lights.


  • Transformer
  • Diodes
  • Capacitors
  • Resistors
  • LEDs
  • 8051 series Microcontroller
  • White LEDs
  • Crystal


  • Keil Compiler
  • Language: Embedded C or Assembly

Friday, June 19, 2015

Arduino LilyPad USB

The LilyPad Arduino is a microcontroller board designed for wearables and e-textiles. It can be sewn to fabric and similarly mounted power supplies, sensors and actuators with conductive thread. The board is based on the ATmega32U4. Board comes fully assembled and tested with ATMega168V pre-loaded with bootloader.

Operating Voltage3.3V
Input Voltage (recommended)3.8V
Input Voltage (limit)5V
Digital I/O Pins9
PWM Digital I/O Pins4
Analog Input Pins4
DC Current per I/O Pin40 mA
Flash Memory32 KB (ATmega32u4) of which 4 KB used by bootloader
SRAM2.5 KB (ATmega32u4)
EEPROM1 KB (ATmega32u4)
Clock Speed8 MHz
Radius18 mm

Tuesday, June 16, 2015


The Raspberry Pi 2 Model B is the second generation Raspberry Pi. It replaced the original Raspberry Pi 1 Model B+ in February 2015. Compared to the Raspberry Pi 1 it has:
  • A 900MHz quad-core ARM Cortex-A7 CPU
  • 1GB RAM
Like the (Pi 1) Model B+, it also has:
  • 4 USB ports
  • 40 GPIO pins
  • Full HDMI port
  • Ethernet port
  • Combined 3.5mm audio jack and composite video
  • Camera interface (CSI)
  • Display interface (DSI)
  • Micro SD card slot
  • VideoCore IV 3D graphics core

Sunday, May 24, 2015

Voltage, Current and Resistance

Voltage, Current and Resistance

The relationship between VoltageCurrent and Resistance forms the basis of Ohm’s law which in a linear circuit states that if we increase the voltage, the current goes up and if we increase the resistance, the current goes down. Then we can see that current flow around a circuit is directly proportional (  ) to voltage, ( V↑ causes I↑ ) but inversely proportional ( 1/∝ ) to resistance as, ( R↑ causes I↓ ).
  • Voltage or potential difference is the measure of potential energy between two points in a circuit and is commonly referred to as its “ volt drop ”.
  • When a voltage source is connected to a closed loop circuit the voltage will produce a current flowing around the circuit.
  • In DC voltage sources the symbols +ve (positive) and -ve (negative) are used to denote the polarity of the voltage supply.
  • Voltage is measured in “ Volts ” and has the symbol “ V ” for voltage or “ E ” for energy.
  • Current flow is a combination of electron flow and hole flow through a circuit.
  • Current is the continuous and uniform flow of charge around the circuit and is measured in “ Amperes ” or “ Amps ” and has the symbol “ I ”.
  • Resistance is the opposition to current flowing around a circuit.
  • Low values of resistance implies a conductor and high values of resistance implies an insulator.
  • Resistance is measured in “ Ohms ” and has the Greek symbol “ Ω ” or the letter “ R ”.

Wednesday, February 18, 2015

LDR: Light Dependent Resistor

Light dependent resistor(LDR), also called as Cadmium Sulphide (CdS) cell or photoresistor is a resistor whose value depends upon the incident light intensity. In darkness, the resistanceof LDR becomes high and in light, the resistance gets low.

Dark Sensor Using 555
The following circuit works as a dark sensor. If the light falling on LDR is blocked, it switches on the LED D1. It has been configured in monostable mode of 555 timer which means that the circuit switches on the LED D1 for a specific time. The switching time is determined by the combination of resistance R1 and capacitor C1.
In this circuit, time (T) = 1.1xR1xC1 = 1.1x47x103x100x10-6= 5.17sec.

Touch Sensor using 555
We can make the previous dark sensor circuit work as a touch sensor by making small changes in the schematic. We just need to remove the LDR, put a small wire and connect it to the coupling capacitor. Note that the electrode wire connected to capacitor C2 should be around 2-5cm long. As we touch on the wire, the circuit triggers the LED for a specific time as determined by the resistor R1 and capacitor C1.  You can connect the wire to a small metallic touch plate using an alligator clip.

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.