Electronics Projects

Fire alarm

2012-07-25T16:41:00.001+05:30

At times we forget to switch off our heating devices and eventually they get damaged. Therefore there is always a need of a device which can alert by sounding an alarm if the device temperature goes beyond a particular value. Same concept can be used in fire alarm. If a building catches fire then it will raise an alarm and people could evacuate the building.

This fire alarm circuit is based around LM35 which is a temperature sensor and could be used to switch an alarm when temperature goes beyond a preset value. In this circuit the output of LM35 is fed to the negative pin of comparator of LM339. The positive input is connected to a preset VR1 of value 10K. This preset is used to set the reference temperature. If output of LM 35 is less than V reference than the output of comparator is low. The IC LM339 has four inbuilt comparators.

The output of comparator is fed to the base of transistor T1(BC547). As the output is low, T1 is in the cut off state and behaves like an open switch. As a result point A is at high potential. This in turn biases the transistor T2, which behaves like a closed switch. The potential of point B is low, which in turn gives a low signal to the reset pin 4 of the IC 555. When the reset pin is low, there is no output at the output pin 3 and hence the buzzer does not sound.

When the temperature exceeds the reference temperature, the output of the comparator becomes high and T1 gets biased. The point A comes at a low potential thereby making the point B at higher potential. Since the point B is connected to the reset pin, it also becomes high and the 555 timer which is configured in the astable mode, starts producing pulses and the buzzer makes a sound to alert the rise in temperature.

Variable power supply

2012-07-25T16:37:00.003+05:30

The electronic devices are very sensitive to the fluctuations in the power fed to them. This problem can be solved by using regulated power supply for them. This power supply circuit is equipped with an adjustable voltage regulator to adjust the output in accordance with the requirement. Adjustable voltage regulators have both line and load regulation which is better than standard fixed regulators.

The stepped down AC from the secondary winding of the transformer is fed to the bridge rectifier for rectification. The output has pulsating DC which is filtered by a capacitor C1 (1000uF). This output needs to be stabilized against the input variations by using a voltage regulator IC (LM317) in series with the bridge rectifier. This regulator not only guarantees stable output but can also be adjusted to obtain a desired level of voltage output. The output from the regulator can be varied from 1.2V to 25V. This is achieved by adjusting the value of variable resistor (preset) VR1 (5k). A fixed resistor R1 (220) along with VR1 forms a potential divider. A capacitor C2 (0.1uF) is used to suppress the oscillations, if any, produced in the voltage regulator.

Light sensor using photodiode

2012-07-25T16:31:00.001+05:30

The light sensor circuit shows the application of photodiode to detect the presence of light. This light sensor can be used as an intermediate circuit in various applications to detect the presence or absence of light. The sensitivity of the sensor can be adjusted using the preset.

A photodiode, used as a photo detector, generates current in the circuit when light incidents on it. This circuit uses the photodiode in reverse bias mode with resistor R1(10k). This resistor does not allow too much current to flow through the photodiode in case a large amount of light falls on the detector. Initially when no light falls on the photodiode, it results in high potential at the inverting input of a comparator (pin6) of LM339. When light falls on the photodiode, it allows current to flow through the diode, and thus drops the voltage across it. The non-inverting input (pin7) is connected to a variable resistor VR2 (preset) which is used to set the reference voltage of the comparator. A comparator works on the principle that its output remains high as long as the non-inverting input is at higher level than that at its inverting input. Here, the output (pin1) is connected to an LED. The reference voltage is set to correspond to a threshold illumination through a preset VR1 (10k).

The LED at the output will glow when light falls on the diode. In such a condition, the inverting input drops to a lower value than the reference set at the non-inverting input and so the output goes providing the necessary forwards bias to the LED.

Music transfer by IR by amplification

2012-07-19T17:17:00.003+05:30

The circuit can be broadly divided into two parts: the transmitter and the receiver. The transmitter consists of a condenser mic, which is used as sound sensor to convert the sound signals into electrical signals. The electrical signals are amplified by the amplifying unit. For details about the amplifying unit refer to Sound Amplifier. Since the strength of the amplified output from the transistor is not enough for IR transmitter to produce high energy IR signals, so the amplified signals are further amplified using an Op-amp as amplifier with negative feedback configuration. The amplification factor is decided by the resistors R6 (1K) and R7 (10K). The output voltage is determined according to the formula V0=-(R7/R6)*Vin. This amplified signal is transmitted through the IR LED.

The receiver receives the IR signals through an IR receiver and converts them back to sound signals through a speaker. For details of receiver section refer to Sound/Voice transmission through IR. This circuit has a better range since the strength of the transmitted signals is high. This circuit can operate at a range of around 10-15 cm.

DTMF Decoder

2012-07-19T17:10:00.002+05:30

DTMF (Dual tone multiple frequency) is the most popular and nowadays ubiquitously used telecommunication signalling method. A DTMF decoder detects the DTMF tones and generates the binary sequence corresponding to key pressed in a DTMF keypad. The circuit presented here is a DTMF decoder. DTMF keypads are used in almost all landline and mobile handsets. The DTMF decoders, therefore, are used at the telephone switching centres to detect the number dialled by the caller. The DTMF version used in pushbutton telephones is called touch tone and is a registered trademark of AT&T.

The circuit uses a DTMF decoder IC (HT9170). The DTMF tones are generated by the keypad of a cell phone or by the computer software available on www.polar-electric.com.

The tones generated from the speaker (audio signals) of keypad are given to microphone which converts audio tones into electrical signals. The signals from the microphone are processed by the DTMF decoder IC which generates the equivalent binary sequence as a parallel output.

The electrical signals from microphone (mic) are fed to inverting output (pin2; VN) of Op-amp, present in IC, through a series of resistance and capacitance of value 100 k and 0.1 µF respectively. The non-inverting input pin (pin1; VP) of Op-amp is connected to pin4 (V_REF). The voltage at V_REF pin is V_DD/2. A feedback signal is provided, by connecting the output of Op-amp (pin3; GS) to inverting input pin (pin2; VN) through a resistor R2 (100 k).

The output of Op-amp is passed through a pre filter. The output from this pre filter is then supplied to low group and high group filters. These filters consist of switched capacitors and divide DTMF tones into low and high group signals. High group filters pass the high frequencies while low group filter pass low frequencies. These frequencies are then passed through frequency detector and code detector circuits. Finally the four-digit code is latched on the output pins of HT9170. The output on these pins has been used to drive a set of four LEDs.

The whole process, from frequency detection to latching of the data, is controlled by steering control circuit. So it is very important part of the whole process and is mainly controlled by RT/GT and DV pins of DTMF decoder IC. RT/GT pin is connected to V_DD through a capacitor of 0.1 µF. The EST pin is connected to RT/GT pin through a resistor of 300k.

Pin6, PWDN pin (active high) inhibits the working of oscillator thereby stopping the working of circuit; and Pin5, INH pin (active high) inhibits detection of the tones of character A,B,C,D. The pin 10; OE (output enable; active high) enables the latching of the data on the data pins. Pin15; DV (Data valid pin) becomes high on detection of valid DTMF tone otherwise it remains low. An oscillator of frequency 3.579545 MHz is connected between pins 7 and 8.

Infrared sensor

2012-07-19T17:03:00.002+05:30

This circuit is one of the most basic and popular sensor modules. In electronics, this sensor is analogous to human’s visionary senses which can be used to detect an obstacle which is one of its common applications. In robotics, a group of such modules are used so that a robot can follow a line pattern.

The transmitter part of the sensor is an Infrared (IR) Led which transmits continuous IR rays to be received by an IR receiver. The output of the receiver varies depending upon its reception of IR rays. Since this variation cannot be analyzed as such, therefore this output can be fed to a comparator. Here operational amplifier (op-amp) of LM 339 is used as comparator.

When the IR receiver does not receive signal the potential at the inverting input goes higher than that that at non-inverting input of the comparator (LM 339). Thus the output of the comparator goes low and the LED does not glow .When the IR receiver receives signal the potential at the inverting input goes low. Thus the output of the comparator (LM 339) goes high and the LED starts glowing. Resistor R1 (100), R2 (10k) and R3 (330 ) are used to ensure that minimum 10 mA current passes through the IR LED, photodiode and normal LED, respectively. Resistor VR2 (preset=5k) is used to adjust the output. Resistor VR1 (preset=10k) is used to set the sensitivity of the circuit.

Automatic night lamp

2012-07-19T16:52:00.001+05:30

Ever imagined how the street lights would turn on automatically in the evening and go off in the morning? Is there anyone who comes early morning to turn off these lights? The following circuit can perform this job properly. This circuit uses the output from a simple light/dark activated circuit and drives a relay in its output which can be further coupled to switch on/off an electrical appliance in a household.

An appliance can be made dark or light activated by slightly changing the circuit’s configuration. This idea finds numerous applications such as, automatic watering of gardens at evening, automatic night lamp, dark activated siren and so on.

A light dependent resistor (LDR) is used in this circuit to provide input to a comparator of LM339 (refer Automatic lightdark indicator). The output pin of the comparator goes high depending on the configuration of LDR so that it can be made light or dark activated. This output is connected to a transistor T1 (BC 547) which acts as a switch for the relay.

The high output of the comparator provides the necessary forward bias to the base-emitter junction of the transistor T1. Thus T1 jumps from cut off to saturation state and collector current flows. This collector current energizes the relay coil. The magnetic field produced by the relay coil shifts its connection from NO state to NC. An appliance connected to NC contact gets switched on.

When the output of the comparator is low, it is insufficient to drive the transistor T1 to saturation. Hence T1 moves to cut off and the collector current ceases to flow. Thus the relay coil gets de-energized and it switches the state from NC to NO mode. It is important to note that resistor R2 (20k) is provided at the base of T1 to check the base current.

Touch Based Blinking Lights

2012-06-24T19:28:00.002+05:30

This circuit demonstrates the principle and operation of application based on touch sensor. The circuit is divided into three parts: Input, 555 timer and output. A touch plate is used for the input and output can be seen across an LEDor a buzzer. Some application of the circuit include touch based blinking lights, touch buzzer, touch switch etc.
Click Here

The touch plates is connected to the trigger pin of the 555 timer IC. When we touch the touch plates the output of the touch plates becomes zero thereby providing an active low trigger to the IC 555. The IC is configured in the monostable mode .The output of the IC is a pulse whose frequency is set by the resistor (R1) and capacitor (C1) according to the formula [F=1/(1.1*R*C)]. In this case it produces a pulse with frequency of about 0.9 hertz and time period of 1.1 seconds. In monostable mode pin7 (discharge pin) and pin6 (threshold pin) are shorted while R1 is connected between pin7 and Vcc and C1 is connected between pin 6 and ground. Reset pin (pin4) is connected to Vcc while control pin is connected to ground through a capacitor. The output can be observed on the LED, which glows for a small duration. This circuit can be used in the following applications:

To detect stray voltages produced by mains or to detect electrostatics build up in a room.

To make touch buzzers.

To implement touch switches like for a bell.

circuit 2, shows an improved version of this circuit. This circuit has a higher sensitivity as compared to circuit in figure 1. The output of the touch plate is connected to the base of npn transistor T1 (BC 547). The collector is connected to the Vcc through a resistor R1. The trigger pin of the IC is connected to the collector of the transistor. When no input is there on the base of the T1, T1 is in cut off state and hence the trigger pin is at logic high and therefore 555 do not produce any output. When we touch the plates T1 behaves like a closed switch trigger pin gets connected to ground, thereby producing the output at pin 3 of the IC.

Digital code lock using 8051 microcontroller (AT89C51)

2012-06-16T17:15:00.000+05:30

An digital lock is a device which has an electronic control assembly attached to it. They are provided with an access control system. This system allows the user to unlock the device with a password. The password is entered by making use of a keypad. The user can also set his password to ensure better protection. The major components include a keypad, LCD and the controller AT89C51 which belongs to the 8051 series of microcontrollers. This article describes the making of an electronic code lock using the 8051 microcontroller.

A 4x3 matrix keypad and a 16x2 LCD have been used here. Keypad and LCD are very commonly used input & output devices, respectively. A four digit predefined password needs to be specified the user. This password is stored in the system.

While unlocking, if the entered password from keypad matches with the stored password, then the lock opens and a message is displayed on LCD. Also an output pin is made high to be used for further purpose.

The connections in the circuit are as following: port P2 of microcontroller AT89C51 is used as data input port which is connected to data pins (7-14) of LCD. P1^0, P1^1 and P1^2 pins of microcontroller are connected to control pins RS, RW and EN of LCD. Port P0 is used to take input from keypad. P0^7 has been used as lock output pin of controller.

As the program starts, string ‘Enter Password’ is displayed on LCD. The keypad is scanned for pressed digits one by one. Every time, row and column of the key pressed is detected and a ‘*’ is displayed on LCD corresponding to the entered number. After the four digits are entered, the user is prompted to ‘Confirm Password’ and again the input is taken through LCD. If the passwords do not match, a message is displayed to indicate ‘Wrong Password’; otherwise the user is prompted to unlock the device.

To unlock, user needs to ‘Enter Password’ through keypad. Again the keypad is scanned for pressed keys and corresponding digits are identified. The passkey is displayed as ‘****’ on the LCD screen. After the four digits are entered, they are compared with the pre-set password. If all the four digits match with set password, LCD displays ‘Lock Open’ and the lock output pin goes high. If the security code is wrong, ‘Wrong Password’ is sent to be displayed on LCD. The system gets locked if more than three attempts are made with wrong password to open the electronic lock. The system needs to be reset in such a case.

2 in 1 Room Bell

2012-06-14T16:17:00.001+05:30

The roombells are used to produce a ringing alert sound so that the resident comes to know that a visitor is there on the door. Many homes have two doors for entering. So at times it is confusing for the resident to find out on which door is the visitor present. This roombell circuit produces two different sounds can be used simultaneously on both the doors.

The roombell circuit is made up of CMOS LSI designed UM3561 IC which consumes less power. It is commonly used in toys and alarm watches because of its low cost. A compact sound module can be constructed using this IC. It includes oscillator and selector circuit and only few components are required to be added externally. It also contains a programmed ROM to produce siren sound.

When the switch S1 or S2 is pressed, the pin1 or pin5 of the IC1 receives the high signal which is used to drive the transistor that is connected to pin3 of IC1. Hence the speaker gets the supply and IC1 produces the sound of siren so as to indicate the presence on the door. A transistor is used for the process of amplification as the output of pin3 is very low.

Many other different sounds can be produced by referring the datasheet of UM3561. Similarly many other ICs are there to produce different sounds i.e. UM3481, UM3484, and UM34811.

USB Cell Phone Charger

2012-06-14T16:11:00.002+05:30

Nowadays mobiles can also be charged using the USB outlet of PC. The Cell Phone charger circuit presented here can give 4.7V of synchronized voltage for charging the phone. As USB outlets can give 5V DC and 100mA of current. It is sufficient for slow charging of mobile phones so they can be used to charge the mobile phones. USB stands for Universal Serial Port. It is one of the latest methods to exchange information from PC to the real world. The USB port offers power to the external devices. +5V of power is available at pin1 and -5V of it is available at pin4.

Most of the Mobile Phones battery are rated 3.6 volts at 1000 to 1300 mAh. These battery sets have 3 Lithium cells which have 1.2 volt rating. Typically a battery pack sufficiently requires 4.5 volts and 300-500 mA current for fast charging. But low current charging is preferred to increase the efficiency of the battery. The circuit described here provides 4.7 V of the regulated voltage and a sufficient amount of current for the slow charging of the mobile phones. Regulated output is given by the transistor T1, output voltage is controlled by Zener diode ZD and the polarity of the output supply is protected by D1. Front end of the circuit should be connected to an A type USB plug, a red wire to pin1 and black wire to pin 4 of the plug for easy polarity recognition. The output of a suitable charger pin should be connected with the mobile phone. After the circuit is assembled, USB plug should be inserted into the socket and output should be measured from the circuit. If the output is OK and polarity is correct, connect it with the mobile phone and if the polarity is incorrect, it will destroy the mobile battery so extreme care should be taken.

For making this circuit a USB cable is used with at least one male plug on it and strip back about 5 cm of the outer insulation with shield from the bare end of the USB cable. Normally, USB cables have four wires i.e. red, green, white and black. As green and white carry the data so they can be trimmed as they have no use here.. Mostly black wire is NEGATIVE and red is POSITIVE. The voltage across USB is about 5V with 500 mA as maximum current for any device. Now power lines are connected to the USB plug with correct polarity. Reflectors are used for LEDs to get maximum illumination.

How to interface LEDs with 8051 microcontroller (AT89C51)

2012-06-14T13:46:00.000+05:30

This article introduces you to the very basic operation of taking an output from the microcontroller AT89C51. It demonstrates the principle behind interfacingLEDs with 8051 microcontroller. Here we have demonstrated the aforesaid principles by blinking LEDs continuously i.e., switching them on and off.

AT89C51, which belongs to the family of 8051 series of microcontrollers, is very commonly used by a large community of hobbyist and engineers. Its simplicity and ease of programming with inbuilt features easily makes its position in the top preferred list of microcontroller for both beginners and advanced user.

LEDs are by far the most widely used means of taking output. They find huge application as indicators during experimentations to check the validity of results at different stages. They are very cheap and easily available in a variety of shape, size and colors.

The principle of operation of LEDs is simple. The commonly available LEDs have a drop voltage of 1.7 V and need 10 mA to glow at full intensity. The following circuit describes “how to glow an led”.

The value of resistance R can be calculated using the equation, R= (V-1.7)/10 mA. Since most of the controllers work on 5V, so substituting V= 5V, the value of resistance comes out to be 330 ohm. The resistance 220 ohm, 470 ohm is commonly used substitute in case 330 ohm is not available.

AT89C51 is a 40 pin microcontroller which belongs to 8051 series of microcontroller. It has four ports each of 8 bits P0, P1, P2 and P3.The AT89C51 has 4K bytes of programmable flash. The port P0 covers the pin 32 to pin 39, the port P1 covers the pin 1 to pin 8, the port P2 covers the pin 21 to pin 28 and the port P3 covers the pin 10 to pin 17. Pin 9 is the reset pin. The reset is active high. Whenever the controller is given supply, the reset pin must be given a high signal to reset the controller and bring the program counter to the starting address 0x0000. The controller can be reset by manually connecting a switch or by connecting a combination of resistor and capacitor as shown in the circuit diagram. A 12 MHz crystal is connected between pin 18 pin 19. Pin 40 is Vcc and pin 20 is ground. Pin 31, is connected to Vcc as we are using the internal memory of the controller

LEDs are connected to the port P0. LEDs need approximately 10mA current to flow through them in order to glow at maximum intensity. However the output of the controller is not sufficient enough to drive the LEDs, so if the positive leg of the LED is connected to the pin and the negative to ground as shown in the figure, the LED will not glow at full illumination.

To overcome this problem LEDs are connected in the reverse order and they run on negative logic i.e., whenever 1 is given on any pin of the port, the LED will switch off and when logic 0 is provided the LED will glow at full intensity.

As soon as we provide supply to the controller, the LEDs start blinking i.e., they become on for a certain time duration and then become off for the same time duration. This delay is provided by calling the delay function. The values inside the delay function have been set to provide a delay in multiples of millisecond (delay (100) will provide a delay of 100 millisecond).

How to display text on 16x2 LCD using AVR microcontroller (ATmega16)

2012-06-08T14:34:00.001+05:30

This article is in continuation to the article Single character LCD display using AVR. The aforesaid article shows how to display a single letter on LCD. Moving forward towards learning to work with LCD, this article explains how to display a string on LCD. Displaying string is occasionally used in many applications.

The connection of the LCD with the AVR microcontroller (ATmega16) is shown in the circuit diagram. A string is nothing but a sequence of characters. The following steps explain how to display a string on the LCD.

To send string on LCD:

i. Make a string pointer variable

ii. Pass the starting address of string to that pointer variable

iii. Pass the string pointer value to the LCD_write function

iv. Increment the pointer value and go to step (iii.) till the value of pointer reaches NULL character.


void LCD_write_string(unsigned char *str) //store address value of the string in pointer *str

{

 int i=0;

 while(str[i]!='\0')    // loop will go on till the NULL character in the string 

 {

  LCD_write(str[i]);    // sending data on LCD byte by byte

  i++;

  }

 return;

}

How to interafce 16x2 LCD with AVR microcontroller (ATmega16)

2012-05-23T16:33:00.001+05:30

In this project LCD is working in 8-bit mode i.e., the data transferred to the LCD must be in 8-bit data form. The PortA of ATmega16 is connected to data pins of LCD and is defined as LCD_DATA. PortB is defined as control pins (Rs, R/W and En).

Conceptually, interfacing LCD with AVR microcontroller is similar to that of interfacing it with any other microcontroller.

The following steps explain in detail how LCD can be interfaced with ATMEGA 16:

Step1: To initialize LCD

The following instructions are used to initialize LCD.

· 0x38 to initialize LCD in 8-bit mode

· 0x01 to clear LCD

· 0x0E to make cursor ON

· 0x80 to go to first line and 0^th position in LCD

Delay of around 50 micro second is necessary b/w two commands for execution of instructions.


void init_LCD(void)

{

 LCD_cmd(0x38);  // initialization of 16X2 LCD in 8bit mode

 _delay_ms(1);



 LCD_cmd(0x01);  // clear LCD

 _delay_ms(1);



 LCD_cmd(0x0E);  // cursor ON

 _delay_ms(1);



 LCD_cmd(0x80);  // ---8 go to first line and --0 is for 0th position

 delay_ms(1);

 return;

}

Step2: Define command function

To send any command to LCD

· Transfer the command to LCD_DATA port

· Set RS and RW bit to go LOW and enable as HIGH

· Give a small delay

· Set enable to LOW


void LCD_cmd(unsigned char cmd)

{

 LCD_DATA=cmd;

 ctrl =(0<<rs)|(0<<rw)|(1<<en); // RS and RW as LOW and EN as HIGH

 _delay_ms(1);

 ctrl =(0<<rs)|(0<<rw)|(0<<en); // RS, RW , LOW and EN as LOW

 _delay_ms(50);

 return;

}

Step3: Define write function

To display any data on LCD

· Transfer the data (Ascii value of the character to be sent) to LCD_DATA port.

· Make RW as LOW and set RS and enable as HIGH.

· Give a small delay.

· Make enable pin LOW


void LCD_write(unsigned char data)

{

 LCD_DATA= data;

 ctrl = (1<<rs)|(0<<rw)|(1<<en); // RW as LOW and RS, EN as HIGH

 _delay_ms(1);

 ctrl = (1<<rs)|(0<<rw)|(0<<en); // EN and RW as LOW and RS HIGH

 _delay_ms(50);   // delay to get things executed

 return ;

}

Simple 12 Volt Day Night Switch

2012-05-18T16:42:00.003+05:30

At times it’s really very annoying to see the street lights kept switched ON even during broad day light. The present circuit of an automatic night light can very effectively put an end to this problem. Read here how to build it.

We all know how important it has become to save electricity in today’s circumstance where it is getting difficult to fulfill the power requirements for our cities. Today everybody along with the politicians and the official authorities are busy putting forth their own opinions regarding the issue. But ironically at times we find the street lights kept switched on even during broad daylight, and this clearly shows how irresponsible these men can be. So instead of depending on these officials, why not take some help from electronics and find a solution to get the work done automatically? A simple circuit of an automatic night light described in this article can very accurately switch ON a load (street lights for example) when darkness falls and switch it OFF when dawn breaks.

How the Circuit Functions

A single NAND gate, a PNP transistor and few other passive components are the only things needed to construct this useful gadget. The circuit description can be understood from the following explanation:

As shown in the diagram a single NAND gate N1 from the IC 4093 is configured as an inverter and a voltage monitor.
A reference voltage can be set at its input with the help of VR1. This adjustment will set the level of darkness at which the system will change state.
An LDR (Light Dependent Resistor) which is also connected at the input of N1 is used to sense a difference in light levels. A LDR is in fact a resistor which changes its value with a change in the intensity of light falling on it.
In the absence of light or when its dark, the LDR offers an infinite resistance and thus the input of N1 is kept at logic high due to the voltage received through VR1. This means that at this instant the output of N1 is logic low, the relay is activated through T1 and the lights (load) connected to the relay contacts are switched ON.
With an increase in the ambient light the resistance of the LDR will gradually fall and after a certain level the input of N1 will become logic low. Immediately its output will go high switching OFF the transistor, the relay and the lights.
Capacitor C1 has been kept to avoid the relay from chattering during twilight threshold levels.

How to Build and Install the Unit

The entire circuit of this 12 volt day night switch can be built over a small piece of general PCB and the whole assembly along with the transformer may be housed inside a good looking ABS plastic enclosure. Only the LDR has to be fixed over the box so that it can sense the ambient daylight.

Take due care to position the LDR in such way that no other stray light or the light which it’s controlling is able to be incident on it, or else it may produce false switching and may start oscillating. The best position would be to install the unit at a point much higher than the lights which are controlled by it.
This automatic night light system may also be appropriately used to control building porch lights, neon signs, large advertising displays, gallery lights and also as automatic house interior decorative lights. Thus this simple inexpensive circuit should not only be able to relieve you from the headache of timely switching the particular lights but also will result in quite an economical way of using them.

Automatic LED Day, Night Light Circuit Diagram

Interface LED with AVR Microcontroller

2012-05-15T16:01:00.000+05:30

All the four ports can be configured to read an input from some external device or to give output to any external device as per the application. For e.g., a switch is connected to a particular pin, that pin should be configured as input to read the values from the switch (external Device in this case) and if you are connecting a LED to any pin of the port then that particular pin should be configured as output to transmit the signal to the LED (external device in this case). A single port can be configured such that some of the pins of the same port are input and some are output.

Configuring IO Ports:

Every port (PORTx, x = A or B or C or D) of AVR microcontrollers have three registers associated with it:

1. DDRx: Data direction Register, to set the direction of each pin of PORTx and configuring it to be as input or output.

2. PORTx: The values which are to be supplied at the output of the port are written in this register. These values acts as input to the device connected at output port of the microcontroller (through PORTx output configured pins).

3. PINx: This register stores the input value from the external connected hardware, when the port is configured as input port. The input data is read from PINx register.

So the first step in configuring or initializing any of the IO port is to set its direction in data direction register (DDRx) to define the behavior of individual pins as input or output. A high (1) in any bit of the DDRx register means the corresponding pin is set as output and vice versa.

Example: Considering switch-LED scenario, suppose a switch is connected to Pin5 (PORTD.4) of PORTD and LED is connected to Pin8 (PORTD.7) of PORTD. Now we need to initialize the pins accordingly. The other pins of PORTD are not used in this case so they can be ignored as of now.

STEP-1: In order to configure PORTD.4 as input the value of Pin-5 (DDRD.5) in DDRD register is made 0.

DDRD.7	DDRD.6	DDRD.5	DDRD.4	DDRD.3	DDRD.2	DDRD.1	DDRD.0
-	-	0	-	-	-	-	-

Step-2: To initialize PORTD.7 as output the value of Pin-8 (DDRD.7) in DDRD register is made 1.

DDRD.7	DDRD.6	DDRD.5	DDRD.4	DDRD.3	DDRD.2	DDRD.1	DDRD.0
1	-	0	-	-	-	-	-

Step-3: Rest of the pins can have any value as they are not being used in this case. The default values of DDRx register is 0 for each pin i.e., all the ports of AVR microcontrollers are initialized as input.

DDRD.7	DDRD.6	DDRD.5	DDRD.4	DDRD.3	DDRD.2	DDRD.1	DDRD.0
1	0	0	0	0	0	0	0

So the value of DDRD will be initialized as 0x80.

The above command can also be written in this form:

Where, 0b is symbol used to represent binary numbers and following it is the actual 8-bit value.

Setting the pull up value:

All the four ports of Atmega16 are equipped with internal software controlled pull up resistors. Every pin of the ports can be pulled up by setting the values into the register PORTx. Following table illustrates the actual state of the pin with different combination of DDRx and PORTx values.

DDRx	PORTx	I/O State	Pull Up	Description
0	0	Input	No	PORTx pins set as input and pull-ups disabled.
0	1	Input	Yes	PORTx pins set as input with pull up enabled
1	0	Output	No	PORTx pins set as output and pull-ups disabled.
1	1	Output	Yes	PORTx pins set as output with pull ups enabled.

Example: Following commands can be used to disable and enable pull-ups on PORTD.

PORTD = 0xFF; //PORTD pins pulled high.

PORTD = 0x00; //Disable pull up registers.

To understand above commands a simple LED blinking experiment is explained below.

Circuit description:

Connect the circuit as shown in the circuit diagram. There is no crystal in the circuit. This project uses the inbuilt crystal of AVR microcontroller, thereby avoiding the need of external crystal. The value of the internal crystal varies from 1MHz to 8MHz, which can be set using the fuse bits. (Readers may connect the external crystal but modify your fuse bits accordingly. Fuse bits are explained in later articles).

Explanation of code:

#include<avr/io.h>

To include all the input output files for avr microcontroller.

#include<util/delay.h>

WinAvr has in built function for providing delay. To use the delay functions include the above header file.

DDRA=0xFF;

To make port A as output port

PORTA=~PORTA;

Whatever was the value of PORTA compliment it and send back to PORTA.

_delay_ms(1000);

A delay function, gives a delay of 1000 millisecond.

To understand the compilation and execution of the above program, please refer the tutorial Working with AVRstudio.

What is to be observed?

Similarly, a code can be for blinking of LED on all four PORTS. It is observed that all pins are working properly except PC2, PC3, PC4 and PC5 pins. The reason is that the AVR microcontrollers has inbuilt JTAG, which needs to be disabled for using these pins as I/O pins.

Machine only access by authorized operator

2012-05-14T13:28:00.006+05:30

Description
The project is developed to access a machine only by an authorized operator. Here each and every operator in the organization has to maintain one card for his access to the machine. A reader is provided to read the data from the card assigned to the authorized operator. Whenever the data in the smart card is matched with the inbuilt operator’s data in the code then LCD display would indicate that the card is accepted. Optionally a relay can be used to ON/OFF the machine in case access control is required. The power supply consists of a step down transformer 230/12V, which steps down the voltage to 12V AC. This is converted to DC using a Bridge rectifier. The ripples are removed using a capacitive filter and it is then regulated to +5V using a voltage regulator 7805 which is required for the operation of the microcontroller and other components.

Block Diagram

Temperature controlled Fan speed

2012-05-13T14:27:00.001+05:30

Description: Temperature controller can be done by using Electronic circuit, Microprocessor or microcontroller. Now microcontroller is advanced among all above circuits therefore we are using Microcontroller for temperature controlling.
In this project, microcontroller 89s51 forms the processing part, which firstly receives data from ADC. ADC receives data fromtemperature sensor. Then microcontroller 89s51 performs the comparison of current temperature and set temperature as per the logic of program for which microcontroller has already been programmed. The result obtained from the above operation is given through output port of 89s51 to LCD display of relevant data and generated pulses as per the logic program which is further fed to the driver circuit to obtain the desired output of ceiling fan.

Description: The "Temperature Controlled Fan" is designed around the micro-controller. The main blocks of the system are:
Micro-controller board: It is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash Programmable and Erasable Read Only Memory PEROM). The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the MCS-51. Instruction set and pin out. The on chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, it provides a highly flexible and cost effective solution so many embedded control applications.

Temperature Sensor Block: The temperature sensed by using LM 35. The output voltage of LM 35 varies in liner proportion with the temperature. The sensitivity of LM 35 is 10 mV/0C. For 1 0C output of LM35 is 10 mV. For 10 0C output of LM35 is 100 mV.

ADC Block: ADC means analog to digital converter. The output of signal conditioning is in the analog form. But Microprocessorrequires input in digital form for this purpose we have to use ADC. In this project we are using ADC 0808. The reference voltage is +5 V. The resolution of ADC is 20 mV. Therefore for 20 mV output of ADC is (01) H. And for 100 mV output of ADC is (05) H.

Amplifier Block: Output signal from micro-controller 89C51 is weak so we have to amplify that signal. Amplifier block amplifies the signal for driving the final control element i.e. output device. For amplification Transistor BC 547 is used.

Output Block: In this project we are using FAN as output device. If temperature is above set point then Fan is ON so that temperature will start to decrease

Display Block: In this project we are using 16 X 2 intelligent LCD display to display the college name, temperature set point and very important is temperature of “Temperature Controlled Fan”.

Power Block: For our project we require + 5 Volt, - 5 Volt and +12 Volts supply. +5 Volts and. 5Volts is given to Micro-controller board, Temperature sensor, Signal conditioning, ADC etc. +12 Volts are used to drive the relay.

Application and Advantage:
1. This project can be used in Home.
2. This project can be used in Industry.
3. This will help in saving the energy / electicity.

Future Development:
1. We can monitor more parameters like humidity, light and at the same time control them
2. We can send this data to a remote location using mobile or internet
3. We can draw graphs of variations in these parameters using computer

Automatic Room light Controller with Visitor Counter

2012-05-13T14:21:00.001+05:30

Description: Main concept behind this project is to measure and display the number of persons entering in any room like seminar hall, conference room. LCD display placed outside the room displays this value. And when number of persons inside the room are zero, power supply inside the room can be cut using a relay interface.

Description in detail: It mainly consist of following blocks
1. Transmitter: We are going to implement the Person counter module using a 2 transmitters and 2 receivers. We are going to use Infra-Red transmitters because infrared beams are not visible to human eyes. Transmitter used are IR LEDs
2. Receiver: We are going to use a Infrared receiver. It is a active low device which means it gives low output when it receives the Infrared rays.
3. Microcontroller: This is the CPU (central processing unit) of our project. We are going to use a microcontroller of 8051 family. The various functions of microcontroller are like
I. Reading the digital input from two infrared receivers and calculate the number of persons from them. II. Sending this data to LCD so that the person operating this project should read the number of persons inside the room. III. Sensing the password using keypad and to check whether it is a correct password or a wrong password and rotate the stepper motor if the password entered is a correct password. IV. Sending the data to the computer using serial port. This data consist of number of persons inside the room and the status of entered password (Correct/wrong)
4. LCD: We are going to use 16x2 alphanumeric Liquid Crystal Display (LCD) which means it can display alphabets along with numbers on 2 lines each containing 16 characters.
5. PC Interfacing: We are going to use max 232 IC for pc interfacing, the values of number of persons inside the room and the status of entered password (Correct/wrong) will be sent to pc.

Application and Advantage:
1. Can be used in various rooms like seminar hall, where the capacity of room is limited and should not be exceeded. Project will display the actual number of persons inside the room.
2. Can be used in conference room, study rooms in colleges.

Future Development:
1. We can send this data to a remote location using mobile or internet
2. Voice alarm system can be added to indicate that room is full & persons can’t enter inside.
3. This helps in energy conservation.

Robot Operated by Cellphone

2012-05-11T21:33:00.000+05:30

Robot Operated by Cellphone

Description in detail:
On the robot we have mounted a 12V battery as the power supply for the circuit and the motors.
When the user calls the mobile which is mounted on the robot the call is received by auto-answer mode.
As the call continues when the user presses a button on his handset the tone that is generated is decoded by the DTMF decoder and the command is passed to the microcontroller which is pre-programmed.
The Microcontroller then passes the command to the motor driver ICs for motion.

Applications:
1) This robot can be used in the borders for disposing hidden land mines.
2) The robot can be used for reconnaissance or surveillance.
3) The robot can be used anywhere there is the service provider tower of the connection provided that is mounted on the robot.
4) The robot is small in size so can be used for spying.