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
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
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
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
|
