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The 555 timer IC is component like chip that used to variety timer, pulse generation, and oscillator applications. The 555 used for delays time, in a oscillator and in flip-flop. It derivative become one package. In the package consist of two 556 or 558 timing circuit.
a)Astable mode which can operate as an electronic oscillator by connect two external resistors and one capacitor in it specific arrangement. There is no stable output that causing the waveform become high and low continuously. It uses include LED, logic clocks,alarm.
b)Monostable mode which this mode function as a “single-shot” pulse generator where it arranged one push to on switch, 2 resistors and a capacitor of it specific arrangement. It uses include timer, bounce free switches, frequency divider and so on
The cabinet is used to put shoes.It is very difficult for us to find our shoes inside the cabinet when there no light.We also did not know there are danger inside the cabinet.the cabinet must be modify using 555 timer to put LED inside the cabinet.
d) A.The function of the 555 timer:
The 555 timer will trigger LED to light up when the door of the cabinet is open and closed automaticly.
e)B.The advantages of using LED inside the cabinet:
a) Can arranged shoes properly
b) Can see the shoes that we want
c) Can see the danger inside the cabinet such as snake or spider
d) We cannot use torches light to see inside the cupboard
e) Cheap and can find easily
f) Save our energy
within the positive power supply and the ground ,there are connection of 3 resistor,the resistor must be same.Control voltage pin are connected to the latter.
Yellow: Negative input of the comparator are connected to the 2/3 Vcc,while the positive are connected to the Threshold pin
Red: positive input of the comparator are connected to 1/3 Vcc while the negative input are connected to the trigger pin.
Purple: the state of timer is stores by the SR flip flop that are controlled by two comparator, so that the the timer can be rest at any time..
Pink: the output pin can load until 200mA due to the output of flip flop followed with the output stages of the push-pull.
Cyan: the flip flop output on the transistor and the connect to the discharge pin of the component.
GND Ground
The ground pin connects the 555 timer to the negative (0v) supply rail
TRIG Trigger
The negative input to comparator No 1. A negative pulse on this pin “sets” the internal Flip-flop when the voltage drops below 1/3Vcc causing the output to switch from a “LOW” to a “HIGH” state.
OUT Output
The output pin can drive any TTL circuit and is capable of sourcing or sinking up to 200mA of current at an output voltage equal to approximately Vcc – 1.5V so small speakers, LEDs or motors can be connected directly to the output.
This pin is used to “reset” the internal Flip-flop controlling the state of the output, pin 3. This is an active-low input and is generally connected to a logic “1” level when not used to prevent any unwanted resetting of the output.
CONT Control Voltage
This pin controls the timing of the 555 by overriding the 2/3Vcc level of the voltage divider network. By applying a voltage to this pin the width of the output signal can be varied independently of the RC timing network. When not used it is connected to ground via a 10nF capacitor to eliminate any noise.
THRES Threshold
The positive input to comparator No 2. This pin is used to reset the Flip-flop when the voltage applied to it exceeds 2/3Vcc causing the output to switch from “HIGH” to “LOW” state. This pin connects directly to the RC timing circuit.
DISCH Discharge
The discharge pin is connected directly to the Collector of an internal NPN transistor which is used to “discharge” the timing capacitor to ground when the output at pin 3 switches “LOW”.
VCC Supply +Vcc
This is the power supply pin and for general purpose TTL 555 timers is between 4.5V and 15V
g) We put the push button switch at outside edge of the door.When we open the door cabinet, the led inside the cabinet will be turn on and after close the door, for a specific time, the led inside of the cabinet will turn off. This process occur due to the application of monostable mode of 555 timer ic which the initial condition of the circuit at output is 0 due to the Q bar flip flop is high as well as both of the comparator inside the timer is low. Then, once the door is open, the push button will be connected automatically. It then change the 555 timer output state to high and ground the push button cause the input state become zero and comparator will output one . Hence cause the Q bar flip flop to go low and output become high so that LED will be turned on2. After the door is close, at a specific time, which is about 5.5s, the Led will start to turn off automatically. It is because the discharges transistor is turned off so the capacitor will start charging to the R1 until voltage through C1 reach 2/3 of the supplied voltage and causing the threshold high and comparator become one. This will bring the circuit into its initial state which Q bar output become high and activate the discharge transistor as well as make the output ic low again. Thus, we can notice that the amount of time is based on the value of resistor1 and capacitor1 which can determine the time desire by using formula t=1.1 x C1 x R1 .

Features of 555 timer IC
It operating within +5 V until +18 V of voltage supply
The current is loaded in sinking and sourcing is 200mA
Choose the correct external component of the circuit because it timing interval will be done in several minutes so that the frequency will be exceed hundred kilo Hz
The high current of the output causes the output of the 555 timer derive a transistor- transistor logic.
It has a temperature equivalently 0.005 %/ °C.
The timer of the duty cycle can be adjust at any time.
600nW per package is the maximum power dissipation

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