Projects for ECE

Testing LDR

2013-09-02T11:54:00.000+05:30

LDR (light dependent resistance) can be very easily tested by using a digital multimeter. We are aware that the resistance of an LDR varies according to the light falling on it .In bright light LDR resistance will be around 500 Ohms and in darkness the resistance will be around 200 K.Ohm. For a proper testng we need to measure the resistance of the LDR in bright light and in darkness.

Testing in bright light
Keep the multimeter at Resistance checking mode. The LDR must be subjected to a bright light source (day light is enough).Now the multimeter will show a low resistance reading around 500 Ohms.

Testing in darkness
Keep the multimeter at Resistance checking mode. The LDR must be subjected to darkness by covering it with an opaque paper. Now the multimeter will show a high resistance reading around 200K.Ohm

IF both the tests are OK we can conclude that the LDR is working fine

3rd Program

2013-04-30T13:15:00.000+05:30

This is a simple program of adding two numbers which are entered by the user

#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int a,b,c;
cout<<"Enter the first number ";
cin>>a;
cout<<"Enter the second number ";
cin>>b;
c=a+b;
cout<<"Sum = "<<c;
getch();
}

Click here to download

2nd Program

2013-02-28T11:57:00.001+05:30

This is a Simple program to add two fixed numbers

#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int a,b,c;
a=5;
b=44;
c=a+b;
cout<<"Sum = "<<c;
getch();
}

Click here to download

1st program (Display Hello World)

2013-02-28T10:58:00.000+05:30

This program helps to display a line in C++

#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
cout<<"Hello World this is my first C++ Program";
getch();
}

Link to download the Compiled program

Simple Siren using op-amp

2013-02-28T10:37:00.000+05:30

Intoduction :-

Device such as burglar alarms and sirens, whose basic purpose is to monitor certain conditions. The above figure shows a simple siren/alarm circuit using a dual-amp MC1458, audio amplifier LM380, and a 1-W speaker. The dual op-amp is used as a signal generator that produces square, pulse and triangular or sawtooth wave froms.

Operation :-

The A1 and A2 op-amps make up a waveform generator in which the output of A1 is a square wave or pulse waveform and that of A2 is either a triangular or sawtooth waveform. The potentiometer R2 controls the frequency as well as the type of output waveform of op-amps A1 and A2. The switch SW1 connect the output of A1 or A2 to the audio power amplifier LM380, this in turn drives the speaker. Although not used in the circuit of figure 1, a potentiometer may be connected between (+) and (-) inputs of the power amplifier to control its voltage gain, which in turn controls the sound volume. The sound level produced depends on the position of switch SW1, the wiper setting of potentiometer R2, and the value of capacitor C4. Therefore, sound of varying intensities can be obtained by adjusting SW1, R2, and C4.

For higher output power (sound intensities), audio power amplifier may be used in the bridge from. This configuration will also require a higher wattage speaker.

PARTS LISTS :-

R1, R4 = 10 KΩ
R2 = 20 KΩ potentiometer
R3 = 39 KΩ
C1, C3 =0.1 µF
C2 = 100 µF
C4 = 0.05 µF
IC1 = MC1458 (dual op-amp)
IC2 = LM380 (audio power amplifier)
8Ω 1-W speaker
SW1 = Three-position switch

Dancing Lights

2012-10-18T22:51:00.000+05:30

Here is a simple dancing light circuit based on NE555 (IC1) & CD4017 (IC2) . The IC1 is wired as an astable multivariator to provide the clock pulses for the CD4017. For each clock pulse receiving at the clock input (pin14) of I.C. CD4017, the outputs Q0 to Q9 (refer pin diagram of CD 4017) becomes high one by one alternatively. The LEDs connected to these pins glow in the same fashion to give a dancing effect. The speed of the dancing LEDs depend on the frequency of the clock pulses generated by the IC1.

Note:-

The I.C. should be mounted on I.C. base
Using different color of LEDs would produce better visual effects
For testing use a breadboard.

555 Timer IC

2012-07-16T15:53:00.002+05:30

One of the most versatile linear ICs is the 555 timer which was first introduced in early 1970 by Signetic Corporation giving the name as SE/NE 555 timer. This IC is a monolithic timing circuit that can produce accurate and highly stable time delays or oscillation. Like other commonly used op-amps, this IC is also very much reliable, easy to use and cheaper in cost. It has a variety of applications including monostable and astable multivibrators, dc-dc converters, digital logic probes, waveform generators, analog frequency meters and tachometers, temperature measurement and control devices, voltage regulators etc. The timer basically operates in one of the two modes either as a monostable (one-shot) multivibrator or as an astable (free-running) multivibrator.The SE 555 is designed for the operating temperature range from – 55°C to 125° while the NE 555 operates over a temperature range of 0° to 70°C.

Important features of the 555 timer are :

It operates at a wide range from +5V to +18V Supply voltage
sinking or sourcing 200mA current.
high current output , can drive TTL

Pin Configration :

Pin 1: Ground Terminal. All the voltages are measured wrt this terminal.

Pin 2: Trigger Terminal: This pin is an inverting input to a comparator that is responsible for transition of flip-flop from set to reset. The output of the timer depends on the amplitude of the external trigger pulse applied to this pin.

Pin 3: Output Terminal: Output of the timer is available at this pin. There are two ways in which a load can be connected to the output terminal either between pin 3 and ground pin (pin 1) or between pin 3 and supply pin (pin 8). The load connected between pin 3 and ground supply pin is called the normally on load and that connected between pin 3 and ground pin is called the normally off load.

Pin 4: Reset Terminal: To disable or reset the timer a negative pulse is applied to this pin due to which it is referred to as reset terminal. When this pin is not to be used for reset purpose, it should be connected to + VCC to avoid any possibility of false triggering.

Pin 5: Control Voltage Terminal: The function of this terminal is to control the threshold and trigger levels. Thus either the external voltage or a pot connected to this pin determines the pulse width of the output waveform. The external voltage applied to this pin can also be used to modulate the output waveform. When this pin is not used, it should be connected to ground through a 0.01 micro Farad to avoid any noise problem.

Pin 6: Threshold Terminal: This is the non-inverting input terminal of comparator 1, which compares the voltage applied to the terminal with a reference voltage of 2/3 VCC. The amplitude of voltage applied to this terminal is responsible for the set state of flip-flop.

Pin 7 : Discharge Terminal: This pin is connected internally to the collector of transistor and mostly a capacitor is connected between this terminal and ground. It is called discharge terminal because when transistor saturates, capacitor discharges through the transistor. When the transistor is cut-off, the capacitor charges at a rate determined by the external resistor and capacitor.

Pin 8: Supply Terminal: A supply voltage of + 5 V to + 18 V is applied to this terminal with respect to ground (pin 1).

Working Principle :

Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In most applications, the control input is not used, so that the control voltage equals +2/3 VCC. Output of this comparator is applied to set (S) input of the flip-flop. Whenever the threshold voltage exceeds the control voltage, comparator 1 will set the flip-flop and its output is high. A high output from the flip-flop saturates the discharge transistor and discharge the capacitor connected externally to pin 7. The complementary signal out of the flip-flop goes to pin 3, the output. The output available at pin 3 is low. These conditions will prevail until comparator 2 triggers the flip-flop. Even if the voltage at the threshold input falls below 2/3 VCC, that is comparator 1 cannot cause the flip-flop to change again. It means that the comparator 1 can only force the flip-flop’s output high.

To change the output of flip-flop to low, the voltage at the trigger input must fall below + 1/3 Vcc. When this occurs, comparator 2 triggers the flip-flop, forcing its output low. The low output from the flip-flop turns the discharge transistor off and forces the power amplifier to output a high. These conditions will continue independent of the voltage on the trigger input. Comparator 2 can only cause the flip-flop to output low.

From the above discussion it is concluded that for the having low output from the timer 555, the voltage on the threshold input must exceed the control voltage or + 2/3 VCC. They also turn the discharge transistor on. To force the output from the timer high, the voltage on the trigger input must drop below +1/3 VCC. This also turns the discharge transistor off.

A voltage may be applied to the control input to change the levels at which the switching occurs. When not in use, a 0.01 nano Farad capacitor should be connected between pin 5 and ground to prevent noise coupled onto this pin from causing false triggering.

Connecting the reset (pin 4) to a logic low will place a high on the output of flip-flop. The discharge transistor will go on and the power amplifier will output a low. This condition will continue until reset is taken high. This allows synchronization or resetting of the circuit’s operation. When not in use, reset should be tied to +VCC.

16 X 2 LCD

2012-06-30T23:11:00.000+05:30

LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations and so on.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely, Command and Data.

The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD.

Pin Diagram :-

Pin Description:

Pin No	Function	Name
1	Ground (0V)	Ground
2	Supply voltage; 5V (4.7V – 5.3V)	Vcc
3	Contrast adjustment; through a variable resistor	V_EE
4	Selects command register when low; and data register when high	Register Select
5	Low to write to the register; High to read from the register	Read/write
6	Sends data to data pins when a high to low pulse is given	Enable
7	8-bit data pins	DB0
8		DB1
9		DB2
10		DB3
11		DB4
12		DB5
13		DB6
14		DB7
15	Backlight V_CC (5V)	Led+
16	Backlight Ground (0V)	Led-

Simple Proximity Detector

2012-06-29T15:22:00.000+05:30

Description

This is a simple proximity detector using IC CS209. The CS209A is a bipolar monolithic integrated circuit for use in metal detection/proximity sensing applications.The CS209A contains an oscillator set up by an external parallel resonant tank and a feedback resistor connected between pin 2 & 3 .The internal oscillator operates close to the resonant frequency of the tank circuit.As a metal object is brought close to the inductor, the amplitude of the voltage across the tank gradually begins to drop. When the envelope of the oscillation reaches a certain level, the IC causes the outputs to toggle states.potentiometer connected between pin 1 & 8 is adjusted to achieve a certain detection distance range. The larger the resistance the greater the trip-point distance.Detection range can be increased by using a high Q coil.Maximum possible range is 1 inch with a well tuned circuit.Only difficulty in making this circuit is the tuning up the circuit to a particular range.For making it easy place a metal piece at the desired distance from coil (with in 1 inch) and adjust resistance Rf to make one of the outputs ( pin4 or 5) to change state.

Automatic Night Light

2012-06-29T15:10:00.000+05:30

Description.

A cheap and simple automatic night light using few transistors and NE555 timer is shown here. The circuit will automatically switch on the AC lamp when night falls and the lamp will be automatically switched off after a preset time.

The working of this night light circuit very simple. An LDR is used as the sensor here. At day time the resistance of the LDR will be low and so do the voltage drop across it, the transistor Q1 will be in the conducting mode. When darkness falls the resistance of LDR increases and so do the voltage across it. This makes the transistor Q1 OFF. Base of Q2 is connected to the emitter of Q1 and so Q2 is biased on which in turn powers the IC1. NE555 is wired as monostable multivibrator that is automatically triggered at power ON. This automatic triggering is achieved with the help of capacitor C2. The output of IC1 remains high for a time determined by resistor R5 and capacitor C4. When output of IC1 goes high transistor Q3 is switched ON which triggers triac T1 and the lamp glows. A 9V battery is included in the circuit in order to power the timer circuit during power failures. Resistor R1, diode D1, capacitor C1 and Zener D3 forms the power supply section of the circuit. R7 and R8 are current limiting resistors.

Notes :-

R2 Can be used to adjust the sensitivity
R5 @ 4.7M can be used to adjust the on time of the lamp
heat sink should be used for BT136
The wattage of L1 should not exceed 200W

Blinking one LED with 8051

2012-06-29T14:54:00.001+05:30

This is the first project regarding 8051 and of course one of the simplest, blinking LED using 8051. The microcontroller used here is AT89S51 In the circuit, push button switch S1, capacitor C3 and resistor R3 forms the reset circuitry. When S1 is pressed, voltage at the reset pin (pin9) goes high and this resets the chip. C1, C2 and X1 are related to the on chip oscillator which produces the required clock frequency. P1.0 (pin1) is selected as the output pin. When P1.o goes high the transistor Q1 is forward biased and LED goes ON. When P1.0 goes low the transistor goes to cut off and the LED extinguishes. The transistor driver circuit for the LED can be avoided and the LED can be connected directly to the P1.0 pin with a series current limiting resistor(~1K). The time for which P1.o goes high and low (time period of the LED) is determined by the program. The circuit diagram for blinking 1 LED is shown below.

Program :-

Using assembly

START: CPL P1.0
       ACALL WAIT  
       SJMP START

WAIT:  MOV R4,#05H
WAIT1: MOV R3,#00H
WAIT2: MOV R2,#00H
WAIT3: DJNZ R2,WAIT3
        DJNZ R3,WAIT2
        DJNZ R4,WAIT1
        RET

Using embedded C

#include<reg51.h>

void delay(unsigned int)

void main()

{

unsigned char a;

while(1)

{

p1^0=1;

delay(500);

p1^0=0;

delay(500);

}

void delay(unsigned int dtime) // generates a delay of 1ms

{

unsigned int i,j;

for(i=0;i<dtime;i++)

for (j=0;j<1275;j++);

}
}

}

NOTE :-

Well it might look difficult with embedded C but making bigger programs are a lot more easier in embedded c then in assembly

Fan Speed Controller Using LM2941

2012-05-15T00:28:00.003+05:30

Description.
Many electronic circuits related to fan speed controlling have been published here and this one is just another approach. The circuit diagram shown here is of 12V DC fan speed controller using the IC LM2941CT which is a low drop out 1A voltage regulator. The IC has a dropout voltage as low as 0.5 and has also many useful features like power supply reverse protection, thermal protection, short circuit protection etc. The maximum output current the IC can source is 1A.
The 12V DC supply is connected between the Vin (pin4) and ground (pin3) of the IC. The load, which is the fan, is connected across the Vout (pin5) and ground (pin3) of the IC. The network comprising of potentiometers R1, R2 and resistor determines adjust current (Iadj) of the IC. By varying the Iadj using the POT R2 we can adjust the output voltage of the IC and hence the fan speed.

Notes.

The circuit can be powered from 12V DC.
The maximum possible load current is 1A.
A heat sink is recommended for the IC.
POT R1 can be used to adjust the minimum fan speed.
POT R2 can be used to adjust the fan speed.

Thermostat Using LM56

2012-05-11T22:45:00.000+05:30

Description.
Here is the schematic of a very simple electronic thermostat using IC LM56. LM56 is a very accurate dual output low power thermostat from National Semiconductors.LM56 has various useful features like internal temperature sensor, two internal voltage comparators, internal voltage reference etc. Two stable temperature trip points (VT1 and VT2) are created by dividing the LM56′s 1.250V internal voltage reference using 3 external resistors (R1, R2 and R3). There are two digital outputs for LM56 .Output1 becomes LOW when the temperature increases above T1 and goes HIGH when the temperature decreases below (T1±Hysteresis Temperature). In the same way, Output2 becomes LOW when the temperature goes above T2 and goes HIGH when the temperature goes below (T2±Hysteresis Temperature).
By connecting a cooler as the load for relay L1 and a heater as the load for relay L2, a very simple and useful temperature control system can be constructed.

The values of R1, R2 and R3 for the required trip points VT1 and VT2 can be determined using the following equations.
VT1 = 1.250V x (R1)/ (R1 + R2 + R3)
VT2 = 1.250V x (R1 + R2)/ (R1 + R2 + R3)
where:
(R1 + R2 + R3) = 27 k Ohms and
VT1 or T2 = [6.20 mV/degree Celsius x T] = 395 mV therefore:
R1 = VT1/ (1.25V) x 27 k Ohms
R2 = (VT2/ (1.25V) x 27 k Ohms) – R1
R3 = 27 k Ohms – R1 – R2

Notes.

The circuit can be assembled on a Vero board.
Use 5V DC for powering the circuit.
L1 and L2 can be 5V relays.Their current ratings must be selected according to the load they switch.
Do not give more than 10V to LM56.

Zero Degree Celsius Alarm

2012-05-11T22:43:00.000+05:30

Description.

This simple circuit will produce an alarm whenever the temperature falls below zero degree. A thermistor is used here to sense temperature. The op-amp LM7215 is used to compare the reference voltage and voltage from the thermistor network. Reference voltage is given to the non inverting input (pin3) of the IC and voltage from thermistor network is given to the inverting input (pin4).When temperature becomes less than zero degree the voltage at the non inverting input becomes larger than the voltage at the inverting input and the output of the op-amp becomes high. This makes the transistor Q1 ON and drives the piezo buzzer to make the alarm. In the power supply section, IC 7805 is used to derive 5V from the 9V battery.

Notes.

Assemble the circuit on a good quality PCB.
The thermistor used here is a glass bead thermistor, type No: KEYSTONE RL0503-5536K-122-MS (361K @ 0 degree Celsius and 100K @ 25 degree Celsius).
The IC1 must be mounted on a holder.
The battery B1 can be a 9V PP3 battery.

Temprature Controlled LED

2012-05-11T22:39:00.002+05:30

Description.

The circuit is nothing but two LEDs (D1 and D2), whose status are controlled by the temperature of the surroundings. The famous IC LM35 is used as the temperature sensor here. Output of LM35 increases by 10mV per degree rise in temperature. Output of LM35 is connected to the non inverting input of the opamp CA3130.The inverting input of the same opamp can be given with the required reference voltage using POT R2. If the reference voltage is 0.8V, then the voltage at the non inverting input (output of LM35) becomes 0.8V when the temperature is 80 degree Celsius. At this point the output of IC3 goes to positive saturation. This makes the transistor Q1 On and LED D1 glows. Since the base of Q2 is connected to the collector of Q1, Q2 will be switched OFF and LED D2 remains OFF. When the temperature is below 80 degree Celsius the reverse happens.IC1 produces a stable 5V DC working voltage from the available9V DC supply. If you already have a 5V DC supply then you can use it directly.

Notes.

The circuit can be assembled on a Vero board.
IC3 must be mounted on a holder.
The temperature trip point can be set by adjusting POTR2.
Type no of Q1 and Q2 are not very critical. Any general purpose NPN transistors will do it.

IC Voltage Regulator

2012-04-26T00:41:00.003+05:30

IC voltage regulators are versatile and relatively inexpensive and are available with features such as a programmable output, current-voltage boosting, internal short-circuit current limiting, thermal shutdown, and floating operation for high voltage applications-Voltage regulators comprise a class of widely employed ICs. Regulator IC units contain the circuitry for reference source, comparator amplifier, control device, and overload protection all in a single IC. Although the internal construction of IC is somewhat different from that explained in case of discrete voltage regulator circuits, the external operation is almost the same.

A power supply can be built using a transformer connected to the ac supply line to transform the ac voltage to a desired level, then rectifying the ac voltage, filtering with a capacitor and RC filter, if desired, and finally regulating the dc voltage employing and IC regulator. The regulators can be selected for operation with load currents ranging from hundreds of milli amperes to tens of amperes, corresponding to power ratings from milliwatts to tens of watts.

IC regulators are of the following types.

Fixed output voltage regulators: positive and/or negative output voltage.
Adjustable output voltage regulators: positive or negative output voltage.
Switching regulators.
Special regulators.

Except for the, switching regulators, all other types of regulators are linear regulators. The impedance of the active element of the linear regulator may be continuously varied to provide a desired current to the load, on the other hand, in a switching regulator a switch is turned on and off at a rate such that the regulator provides the desired average current in periodic pulses to the load. The switching regulators are more efficient than the linear regulators. This is because there is negligible power dissipation in switching elements in either the on or off state. Nevertheless, in switching regulators the power dissipation is substantial during the switching intervals (on to off or off to on). Also, most of the loads (devices) cannot accept the average current in periodic pulses. Therefore, most practical voltage regulators are of the linear type.

Voltage regulators, especially the switching type, are employed as control circuits in pulse width modulation, push-pull bridges, and series type switch mode supplies. Almost all power supplies make use of some type of voltage regulator IC because they are simple to use, reliable, cheaper in cost, and, above all, available in a variety of voltage and current ratings.

For instance, the LM 309 is a fixed positive regulator with an output of + 5 V, a maximum load current of 1 A, a load regulation of 15 mV, a source regulation of 4 mV, and a ripple rejection of 75 db. For the adjustable regulators, LR and SR are given in percentage rather than millivolts. The table also includes the drop-out voltage, or the minimum permissible difference between the input and output voltages. For example an LM 309 has a drop-out voltage of 2 V. It implies that the input voltage must be at least 2 V greater than output voltage i.e. input voltage must be at least 7 V, because its output voltage is 5 V.New devices can supply load current from 100 mA to more than 5 A. Available in plastic or metal packages, these three-terminal voltage regulators have become extremely popular because they are inexpensive and easy to use. Aside from a couple of bypass capacitors, the new three-terminal IC voltage regulators do not need any external component.

The integrated three-terminal voltage regulators typically incorporate many of the functions discussed so far in a single package, as illustrated in figure.

The error amplifier is used to maintain a constant voltage through a negative feedback. The internal voltage reference is tightly controlled during the fabrication of IC. So, the nominal output voltage of most of the three-terminal voltage regulators has tolerances that range from ± 6 % to better than ±2%. The series-pass element is driven by the output of the error amplifier. IF acts as an automatically controlled variable resistor. This resistance varies as required for maintaining the output voltage constant. The series-pass element is typically a BJT that is rated to pass the maximum load current.

The basic connection of a three-terminal voltage regulator IC to a load is shown in figure. The fixed voltage regulator has an unregulated dc input voltage V_in, applied to one input terminal, a regulated output dc voltage, V_out from a second terminal, with the third terminal connected to ground.

USB Sound Card

2012-04-26T00:38:00.002+05:30

Designing and building a USB sound card is no longer a head ache because we have got the PCM 2702 integrated circuit from Texas Instruments. The PCM2702 is an integrated 16 bit digital to analog converter that has two digital to analog output channels. The integrated interface controller of PCM2702 is compliant to the USB 1.0 standards. The IC can handle sampling rates of 48 KHz, 44.1 KHz and 32 KHz. The IC also has a number of useful features like on-chip clock generator, digital attenuator, play back flag, suspend flag, zero flag, mute function etc. The most interesting thing is that this circuit is plug & play and doesn’t need any driver software for Windows XP and Windows Vista operating systems. The circuit gets control data and audio data from the USB through the D+ and D- pins of the PCM2702 all the data transferring is carried out at full speed. The decoded audio signals will be available at the VOUTL and VOUTR pins of the IC. The 12MHz crystal is connected between the XT0 and XT1 pins of the IC. The VBUS (USB bus power) pin and DGND (digital ground) pins of the IC are connected to the +5V and ground pins of the USB respectively. The circuit requires +5V DC and +3.3V DC for operation and both of these voltages can be derived from the USB port using LDO (low drop out) voltage regulators (not shown in circuit).

Notes.

+5V DC supply can be derived from the USB port using a +5V LDO regulator.
+3.3V DC supply can be derived from the USB port using a +3.3V LDO regulator.
Audio signals (output) available at VOUTL and VOUTR requires further amplification for driving low impedance head phones or loud speakers.
The PCM2702 is available only in SSOP28 package and requires special care while assembling.
Before attempting this circuit please go through the datasheet of PCM2702 and get a clear idea about the device.

12v DC from USB port

2012-04-26T00:36:00.001+05:30

Using this circuit we can convert 5V DC from the computer USB port to 12V DC and a circuit like this will find a lot of application in USB powered systems. The heart of this circuit is IC LT1618 which is a constant current, constant voltage boost converter. The IC has a wide input voltage range of 1.8 to 18V DC and output voltage can be up to 35V DC.

In the circuit resistors R1, R2 sets the output voltage. Pin number 9 is the shutdown pin, less than 0.3V to this pin will shut down the IC. Pin number four is the current sense adjust pin. The current sense voltage can be reduced by applying a DC voltage to this pin. If this adjustment is not needed connect this pin to ground and you can omit components R3, R5 and Q1.

Notes :

C2 and C3 must be rated at least 15V.
Less than 0.3V at the shutdown pin will shutdown the IC.
Output voltage is governed by the following equation R1 = R2 ( (Vout /1.263V) -1).
This circuit can be used to convert 5v to 12v

7 Segment Display

2012-04-13T09:09:00.000+05:30

Seven segment display is a device that can display decimal numbers and are widely used in electronic clocks, electronic meters, digital display panels and a hand full of applications where numerical data is is displayed. The idea of seven segment display is very old and they are in the scenario from early nineteenth century. Seven segment display have seven segments which can be individually controlled (ON/OFF) to display the desired number. Numbers from 0 to 9 can be displayed using various combinations of the segments and in addition to this the hexadecimal letters A to F can be also displayed using a seven segment display. The seven elements (segments) are arranged in the form of a square shaped “8″ which is slightly inclined to the right. The slight inclination to the right is given to improve the readability.Some seven segment displays have an additional dot element which can be used for indicating decimal points. The segments may be based on incandescent bulbs, fluorescent lamps, LCD or LED. Here in this article we give stress to the LED seven segment display.

In an LED 7 segment display, as the name indicates the 7 segments plus the dot segment are based on LEDs. When power is given to a particular segment, it glows and the desired digit can be displayed by powering the suitable combination of LEDs. LED seven segment displays are of two types, common cathode and common anode. In a common cathode display, the cathode of all LED segments are tied together as one common cathode pin and the anode terminals are left alone as input pins. In this scheme the common cathode is always connected to ground and the control signals (active high) are applied to the inputs (anode terminals) .In common anode type display, the anodes of LED segments are tied together as one common anode and the cathode terminals are left alone as input. In this configuration the common anode is always connected to a suitable positive voltage and the control signals (active low) are applied to the inputs (cathode terminals).

USB Lamp

2012-04-13T09:00:00.004+05:30

Here is a simple USB powered lamp that can be used to light your desktop during power failures. The circuit operates from the 5 Volts available from the USB port.The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1. The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter.Two white LED’s are used here for the lamp, you can also use a 2 V torch bulb instead of LED’s. LED D3 indicates connection with USB port.

NOTE

USB port is only able to provide up to 100 mA current.So don’t overload the circuit with more no of LED’s.
Before wiring the circuit confirm the positive and ground leads of USB by a multimeter.
Switch S1 can be used to turn on the lamp.

Testing A Capactor

2012-04-13T08:55:00.000+05:30

This article shows you how to test a capacitor using analogue multimeter. Firstly short the capacitor leads for discharging it completely. Set the multimeter to high resistance mode. Connect the multimeter terminals to the capacitor leads. For electrolytic capacitors the positive terminal of multimeter must be connected to the positive lead of the capacitor and negative terminal of multimeter to the negative lead of capacitor. For other capacitor types, polarity is not an issue.

At the moment you connect the multimeter terminals to the capacitor leads, the multimeter needle will move to zero and then slowly move towards infinity and settle there. This will happen only if the capacitor under test is healthy.

If the capacitor under test is short, the multimeter needle will go to zero and remain there.
If the capacitor under test is open, the multimeter needle will not move (will remain at the infinity position which is the initial position for analogue multi meters).
If the capacitor under test has leakage then the needle will first deflect to zero, and then slowly move towards infinity and will settle at a point before infinity.

This is only a rough test and for complete check up you need to varify the capacitor value using a capacitance meter.

Testing Of Diode

2012-04-13T08:51:00.002+05:30

Diodes are one of the components that can be tested very easily.Ordinary diodes as wells as Zener diodes can be checked by using a multimeter. While testing a diode the forward conducting mode and reverse blocking mode has to be tested separately.

Testing ordinary diode using a digital multimeter.
To check an ordinary silicon diode using a digital multimeter, put the multimeter selector switch in the diode check mode. Connect the positive lead of multimeter to the anode and negative lead to cathode of the diode. If multimeter displays a voltage between 0.6 to 0.7, we can assume that the diode is healthy. This is the test for checking the forward conduction mode of diode. The displayed value is actually the potential barrier of the silicon diode and its value ranges from 0.6 to 0.7 volts depending on the temperature.

Now connect the positive lead of multimeter to the cathode and negative lead to the anode. If the multimeter shows an infinite reading (over range), we can assume that the diode is healthy. This is the test for checking the reverse blocking mode of the diode.

For testing Germanium diodes, the procedure is same but the display will be between 0.25 to 0.3 V to indicate a healthy condition in the forward biased mode. The potential barrier for Germanium diode is between 0.25 and 0.3V.When reverse biased the multimeter will show an infinite reading (over range) to indicate healthy condition.

Testing ordinary diode using analog multimeter.
To check an ordinary Silicon diode using an analogue multimeter, put the multimeter selector switch in a low resistance position (say 1K).Connect the positive lead of multimeter to anode of the diode and negative lead of multimeter to cathode of the diode. If meter shows a low resistance reading, we can assume that the diode is healthy. This is the test for checking forward biased mode of the diode.

Now put the multimeter selector switch in a high resistance position (say 100K).Connect the positive lead of multimeter to cathode of the diode and negative lead to anode of the diode. If the meter shows an infinite reading, we can assume that the diode is healthy. This is the test for checking the reverse blocking mode of the diode. The meter shows infinite or very high resistance reading because a reverse biased diode has a very high resistance (usually in the range of hundreds of K Ohms).

Testing Zener diode.
The forward characteristics of a Zener diode is similar to an ordinary diode.So the methods used for testing forward conducting mode of any ordinary diode is applicable to the Zener diode too.But in reverse mode, the reverse breakdown voltage has great significance and it has to be specifically tested.For example a 5.3V Zener diode must start conducting only when the applied reverse voltage just exceeds 5.3V.The reverse bias mode of Zener diode can be easily tested by using the circuit given below.The resistance R1 can be typically 100Ohms.The multimeter must be in voltage mode.Now slowly increase the output of variable power supply and at the same time observe the voltage shown in the multimeter. The multimeter display increases along with the increase in power supply voltage until the breakdown voltage. Beyond that the multimeter reading stays put despite of the power supply voltage. This is because the Zener diode is now in breakdown region and the voltage across it will remain constant irrespective of the increase in supply voltage and this constant voltage will be equal to the breakdown voltage. If the reading of multimeter in this instant is equal to the breakdown voltage specified by the manufacturer, we can assume that the Zener diode is healthy.

While carrying out this test, remember not to exceed the input excitation voltage to a point that forces the Zener diode to dissipate more power than it can safely handle. Typically current through the diode should not be allowed to exceed more than 10mA.

Automatic Battery Charger

2012-04-12T01:58:00.000+05:30

Here is a 12 volt Lead Acid battery charger that shut off the charging process once the battery attains full charge. This prevents overcharging of the battery so that, the charger can be left unattended. If the terminal voltage of the battery reduces below the set level, say 13.5 volts, the circuit automatically turns on to the charge mode.Charging current as well as the power to the circuit is obtained from a 0-18 volt 2 Ampere step-down transformer. The low voltage AC is rectified by the bridge rectifier comprising D1 through D4 and made ripple free by the smoothing capacitor C1. For charging purpose, 18 volt DC is used while to power the circuit, 9 volt regulated DC from IC1 is used.
IC2 (CA3140) is used as a simple voltage comparator to drive the relay. Its inverting input gets 4.7 volt reference voltage from the Zener ZD, while the non inverting input gets an adjustable voltage through the POT VR1.So normally, the inverting input pin 2 gets higher voltage from the Zener (as adjusted by VR1) and output of IC2 remains low. T1 then remains off keeping the relay off. The charging current passes to the battery through the NC (Normally Connected) contacts of the relay.
When the terminal voltage of the battery increases to 13.5 volts, pin 3 of IC2 gets higher voltage than pin2 and the output of IC2 becomes high. This activates the relay and the contacts break. Charging current to the battery cut off and the relay remains as such since the battery voltage(13.5V or more) keeps the voltage at pin3 of IC2 is higher than that of pin 2.
Setting: Before connecting the battery, set the input voltage to IC2 using a fully charged battery or variable power supply. Turn the switch S1 to the off position and switch on the power. Then connect a fully charged battery/ variable power supply to test points TP observing polarity. Measure the input voltage to pin 3 of IC2.
Slowly adjust VR1 till the input voltage to pin 3 of IC2 raises to 5 volts. At this point, relay should energize and Red LED turns on. Then connect the battery for charging and switch on S1. If the battery takes charge, current to pin 3 of IC2 will be low since most of the current drain occurs into the battery. This keeps the relay off. When the battery voltage increases above 13.5 volts, no more current passes into the battery, so that the voltage at pin3 of IC2 rises and relay turns on.

8051 Microcontroller Basic

2012-04-12T01:25:00.000+05:30

AT89C51 is an 8-bit microcontroller and belongs to Atmel's 8051 family. ATMEL 89C51 has 4KB of Flash programmable and erasable read only memory (PEROM) and 128 bytes of RAM. It can be erased and program to a maximum of 1000 times.

In 40 pin AT89C51, there are four ports designated as P₁, P₂, P₃ and P₀. All these ports are 8-bit bi-directional ports, i.e., they can be used as both input and output ports. Except P₀ which needs external pull-ups, rest of the ports have internal pull-ups. When 1s are written to these port pins, they are pulled high by the internal pull-ups and can be used as inputs. These ports are also bit addressable and so their bits can also be accessed individually.

Port P₀ and P₂ are also used to provide low byte and high byte addresses, respectively, when connected to an external memory. Port 3 has multiplexed pins for special functions like serial communication, hardware interrupts, timer inputs and read/write operation from external memory. AT89C51 has an inbuilt UART for serial communication. It can be programmed to operate at different baud rates. Including two timers & hardware interrupts, it has a total of six interrupts.

Pin Diagram:

Pin Description:

Pin No	Function			Name
1	8 bit input/output port (P₁) pins			P₁.0
2				P₁.1
3				P₁.2
4				P₁.3
5				P₁.4
6				P₁.5
7				P₁.6
8				P₁.7
9	Reset pin; Active high			Reset
10	Input (receiver) for serial communication	RxD	8 bit input/output port (P₃) pins	P₃.0
11	Output (transmitter) for serial communication	TxD		P₃.1
12	External interrupt 1	Int0		P₃.2
13	External interrupt 2	Int1		P₃.3
14	Timer1 external input	T₀		P₃.4
15	Timer2 external input	T₁		P₃.5
16	Write to external data memory	Write		P₃.6
17	Read from external data memory	Read		P₃.7
18	Quartz crystal oscillator (up to 24 MHz)			Crystal 2
19	Quartz crystal oscillator (up to 24 MHz)			Crystal 1
20	Ground (0V)			Ground
21	8 bit input/output port (P₂) pins / High-order address bits when interfacing with external memory			P₂.0/ A₈
22				P₂.1/ A₉
23				P₂.2/ A₁₀
24				P₂.3/ A₁₁
25				P₂.4/ A₁₂
26				P₂.5/ A₁₃
27				P₂.6/ A₁₄
28				P₂.7/ A₁₅
29	Program store enable; Read from external program memory			PSEN
30	Address Latch Enable			ALE
30	Program pulse input during Flash programming			Prog
31	External Access Enable; Vcc for internal program executions			EA
31	Programming enable voltage; 12V (during Flash programming)			Vpp
32	8 bit input/output port (P₀) pins Low-order address bits when interfacing with external memory			P₀.7/ AD₇
33				P₀.6/ AD₆
34				P₀.5/ AD₅
35				P₀.4/ AD₄
36				P₀.3/ AD₃
37				P₀.2/ AD₂
38				P₀.1/ AD₁
39				P₀.0/ AD₀
40	Supply voltage; 5V (up to 6.6V)			Vcc

LM317 Audio Amplifier

2012-04-11T03:15:00.000+05:30

You probably know that LM317 IC is used as an adjustable voltage regulator, but did you know it can be used as an audio amplifier? This is a class A audio amplifier built with LM317 that delivers a maximum 1W audio power.
Use a good heatsink for the LM317 IC and adjust the 5K variable resistor so that you have 4.5V on 10Ω resistor (or LM317 pin 2, Vout).