http://www.engineersgarage.com/contribution/anjali/seven-segment-testing

Tank Full Alarm

Tank Full Alarm

Summary
The circuit describe hear start ringing as soon as the water tank become full hence it help you to check overflow and wastage of water by warning the user  when the tank is about to full as many times it happen we forget to off the motor.
Description
Circuit is based on LM324 which is 14 pin IC consisting of 4 independent operational amplifier in a single package. The output voltage of LM324 is many times higher than the voltage difference between the input terminals of an opamp. This circuit work on very simple concept, But by using this circuit you can prevent overflowing your water tank. After water touching sensors the circuit will give a sound then you can switch off the motor.

The circuit comprises a sensor part built using only one op-amp (N1) of quad op-amp IC LM324. Op-amp N1 is configured here as a comparator. Two stiff copper wires are inserted in the tank containing water. As long as the tank is empty copper wire does not conduct and the circuit remains off.

When the tank dries out, the resistance between the copper wires (sensor probes A and B) increases. As a result output of opamp is high and LED will glow to indicate that tank is empty.
and this will not trigger the IC2. If the resistance increases beyond a preset limit, output pin 1 of op-amp N1 goes ‘low’. This will triggers timer IC2. As a result, LED and buzzer start sounding.
The threshold point at which the output of op-amp N1 goes ‘low’ can be changed with the help of preset VR1.

Components used

IC
IC1(LM324)	1
IC2(CD4011)	1
Resistor
R1-R2(10K)	2
R3(330E)	1
R4(100K)	1
R5(2.2M)	1
R6(180E)	1
VR1(100K)	1
Miscellaneous
Buzzer	1
LED	2

Sound Operated LED

Summary
The LED start glowing as intensity of sound varies. This can be used to measure the intensity of sound present in the room as sound intensity increase number of LED glows also increases.
Description
Circuit is based on LM324 which is 14 pin IC consisting of 4 independent operational amplifier in a single package. The output voltage of LM324 is many times higher than the voltage difference between the input terminals of an op amp.
Working of circuit is very simple we are using LM324 IC as a comparator when input voltage rises above the reference voltage then only we will get the output. When no noise or audio signals is present in the room output voltage on pin 1 is zero because voltage on pin 2 is lower than pin 3 as it work as comparator it will compare the voltage as voltage is less on pin 2 in compare to pin 3 LED will not glow.
As we provide some input noise voltage on pin 2 rises as compare to pin 3 and we will get high on pin1 of IC as a result Led start glowing. Here we are using 1K resistor with between pins a we want that different LED’s should glow on different audio signals and 22K resistor is used to keep the signal input at low level. Mic positive should be connected to supply and negative should be connected to 22k resistor. Intensity of sound signals for which LED must glow on can be varied with the help of variable resistor.
Note –If you want to increase the number of LED then you can use more than one LM324.
Components used

IC
IC1(LM324)	1
Resistor
R1(22K)	1
R2-R5(1K)	4
R6-R9(220E)	4
R10-R11(15K)	2
VR1(10K)	1
Miscellaneous
MIC	1
LED1-LED4	4

Security Guard

Security Guard

Summary
The circuit gives you an audio visual alarm when somebody enters from your door and alerts you. This circuit is based on operational amplifier LM741 and LDR. An op-amp produces an output voltage that is hundreds of thousands times larger than the voltage difference between its input terminals. This can also be used in lockers to protect your valuable things.
Description
The circuit comprises of Operational amplifier μA741  is used as a sensitive voltage comparator, LDR, Preset VR1 which provides reference voltage to the non-inverting terminal pin 3 and LDR and  R1 is connected to inverting pin 2 of IC1 and few more components.

Working of circuit is very simple Install the LDR and LED on opposite side of the door so that light from LED constantly fall on LDR as a result device remain off because light is falling on LDR its resistance is high in comparison to R1 and pin 2 of IC1 goes low. Consequently output pin 6 of IC1 remains high and alarm will not sound. This indicates that nobody is present on the door.  

As soon as anyone open the gate or try to enter from the gate light falling on the LDR is obstructed and its resistance go low. As a result pin 2 of IC1 goes high in comparison to pin 3 of IC1 and pin 6 also become low and LED and buzzer connected to it start sounding giving you a indicator that somebody is present on door.

Components used

IC
IC1(LM741)	1
Resistor
R1-R3(470E)	2
R2(82K)	1
VR1(5K)	1
Capacitor
C1(.1uF)	1
Miscellaneous
Buzzer	1
LED	2

Audio Amplifier

Audio Amplifier

Summary
LM386 is a very popular and widely use 8 pin audio amplifier used to amplify sound signals. The circuit describe below can be used to amplify the sound signals from mobile output, CD player or it can be used in cars to amplify sound signal.
Description
To understand the working of circuit first we should understand its pin description-

Pin 1 and pin 8 is used for gain control of the amplifier.
Pin 2 and pin 3 is used to feed the input signal which is required to be amplified. Pin 2 is used for negative input and pin 3 is for positive signal.
Pin 4 is used as ground.
Pin 6 is used to connect DC power supply.
Pin 5 is used as output.
Pin 7 is used as bypass terminal with a capacitor to prevent oscillation.

Working of the circuit is very simple first we have to adjust its gain factor through pin 1 and 8 if it is left open the gain will be 20 as it is internally set in IC but it can be vary by adding a resistor and a capacitor up to 200. Now feed the required signals to pin 2 and 3. A variable resistor is connected to pin 3 to adjust the sensitivity of input signal and we will get output on pin 5.

C6 is used as current bank for output means when demand for current become low it supplies electrons or when sudden surges of current occur. C5 act as a coupling capacitor remove DC signals and passes only AC signals through it. And we will get the amplified signals through speaker.

Components Used

IC
IC1(LM386)	1
Resistor
R1(1.2K)	1
R2(2.2E)	1
VR1(10K)	1
VR2(5K)	1
Capacitor
C1(470uF)	1
C2,C3,C6(.1uF)	3
C4(10uF)	1
C5(47uF)	1
Miscellaneous
Speaker	1

90 Second Timer

90 Second Timer

Summary
The circuit describes can be used to on and off the device for fix interval of time in this it is 90 seconds. This means device periodically become on for preset time and remain off for same period of time and it can be set with the help of R3 and C1

.
Description
Circuit is based on LM324 which is 14 pin IC consisting of 4 independent operational amplifier in a single package. The output voltage of LM324 is many times higher than the voltage difference between the input terminals of an opamp.
In this pin 12 and 13 are input pin and pin 14 is output pin 4 is for supply and  pin 11 is ground. Working of the circuit is very simple it compares the voltage on pin 13 with respect to pin 12.When power supply is applied output voltage is low as pin 12 is low compare to pin 13 as a result transistor connected to it does not work and relay when remain off.
After some time capacitor starts discharging and voltage at pin 13 become high in comparison to pin12 as a result out pin 14 become high transistor starts conducting and device connected to relay start operating on and off for the time set.
Time period can be set by C1 and R3 when you increase the value time period will increase when you reduce the value time period will decrease.
Components used

IC
IC1(LM324)	1
Resistor
R1-R2,R4(82K)	3
R3(10M)	1
R5(470K)	1
R6(1K)	1
Capacitor
C1(10uF)	1
Miscellaneous
Relay	1
LED	1
T1(BC547)	1

Understanding NOR Gate(CD4001)

Understanding NOR Gate(CD4001)

Summary
CD4001 is the most commonly used Complementary Metal Oxide Semiconductor (CMOS) chip.  It comes in a 14 pin Dual Inline Package (DIP). It has small notch on one side which identifies as pin 1.It consists of 4 independent NOR gate in a single chip. Each gate has 2 inputs and 1 output. Working voltage range of IC is from 5V to 15V. It can deliver approx.10mA at 12V but this can be reduce as power supply voltage reduces.
IC consist of 14 pin in this pin 7 and 14 is connected to battery or DC power supply. Negative is connected to pin 7 and pin 14 is connected to power supply. As we know it has four gates we call it NI1, NI2, NI3, NI4. In first gate NI1 pin 1 and 2 are for inputs and pin 3 is for output. As you can see in the circuit below.     
As we can see in the truth table it will provide the output equal to one when both of the input is low. In another words we will receive the high output when both the signals goes low. And if any the inputs are high we will receive the low output.

Description
The circuit describe below can be used in many application like it can we use as fake light to create an impression that alarm has been fitted or you can use it in your vehicles when your car broke down as it will give eye catching appearance to the car passing near to your vehicle.
To understand the working of NOR gate first built the circuit on breadboard or assemble the circuit on zero PCB  as it require very less components so it can be done easily.
In the diagram above consider that we have supply logic low to pin1 of NI1 as a result we will receive logic 1 in output pin 3 if you have assume pin 2 of NI1 be low. Therefore we will  receive logic 0 at output of pin 4 because 1 is passed to NI2 gate input from pin 3 so whatever may be the input from pin 2 we will receive low at pin 4. This means that we will receive 6V at pin 4. As a result current start following in capacitor and capacitor starts to charging.
Now voltage on pin 8 is also low at this time and assume voltage on pin 9 to be low as a result we will receive high at pin 10 of NI3 which also make pin 12 and 13 of NI4 to high and we will receive low on pin 11 as you can see from truth table and LED connected to it will not glow.
But as capacitor charges voltage on resistor drops to half the power supply NI1 detects a high on in its input pin 2 as a result logic 0 appear on pin 3. Now logic 0 is on pin 5 ad 6 we will receive logic 1 at pin 4 of NI2. As a result pin 8 is also high and now again assume pin 9 to be low now we will receive 0 at output pin of NI3 and as a result output pin ofNI4 will receive high and LED start glowing. From above we can see that for a certain period of time circuit will work and then goes off. Time period of operation can be determine by-T=.7*R*C.
If we assume pin 9 of NI2 to be high then also we will get pin 0 to be high and low as you can now see from truth table.
Component used

IC
CD4001	1
Resistor
R1(2.2)	1
R2(560K)	1
R3(1K)	1
C1(1uF)	1
Miscellaneous
LED1	1