SYAFIQAH Biomedical Electronic Engineering, School of Mechatronic

SYAFIQAH ZAWANAH ZAHRAA’ BT MOHAMED ZAHARI171151491Biomedical Electronic Engineering, School of Mechatronic Engineering, Universiti Malaysia PerlisPerlis, [email protected]

com I. INTRODUCTION 555 timer is one of the most useful Integrated Circuit( IC)s in the electronic circuit and it is used in many projects because it is easy to build which only needed only a few part of external components.555 Timer consists of 2 comparators, 1 Flip-flop , 1discharge resistor , 1 resistive voltage divider . It includes 23 transistors, 2 diodes and 16 resistors at a silicon chip installed in an 8- pin mini dual-in-line package (DIP). Figure 1 Pin in 555 TimerThe 555 timer has 3 principle operating modes:a) Astable mode which can operate as an electronic oscillator by connect two external resistors and one capacitor in it specific arrangement.

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There is no stable output that causing the waveform become high and low continuously. It uses include LED, logic clocks, alarm and so on. Figure 2 astable mode of 555 Timerb)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. Figure 3 Monostable mode of 555 TimerA. Feature of the 555 timer IC• Operates in large range of power from + 5 v to + 18V voltage supply• Sinking or sourcing 200 mA of load current.

• The timer duty cycle can be adjust• As it has high current output , the output can drive a transistor –transistor logic (TTL)• In order to made timing intervals into several minutes along with the frequencies exceeding several hundred kilohertz the external components will need to be choose properly.• The temperature stability of 50 parts per million (ppm) per degree Celsius change in temperature is similar to 0.005%/ °C.• Its maximum power dissipation per package is 600mW.• Lastly, it reset and triggers input has logic compability.II.

FLOWCHARTS/ BLOCK DIAGRAM if closeIII. COMPONENTSA. 555 timer IC or NE 555 The diagram 3.1 shows the NE 555 componet and it symbolPin descriptionPin numbers FunctionPin 1 GROUND TERMNALAll the voltages in the circuit are measured with respect to the grounfPin 2 TRIGGER TERMINAL 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.Pin 3 OUTPUT TERMINALThe 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.Pin 4 RESET TERMINAL When a negative pulse is applied to pin 4 this 555 Timer will be reset and disabled .If this pin is not going to be used as a reset purpose it will be connected to +Vcc to avoid any possibility of false triggering .

Pin 5 CONTROL VOLTAGE Controlled the threshold and trigger levels of this timer in order to modulate the output waveform ,the external voltage will be applied to this pin. Therefore, when the comparator is switched, the amount of voltage applied to this terminal can be decide. If this pin is not going to be used , it should be bypassed to ground through 0.01 micro Farad in order to avoid any noise problem.Pin 6 THERSHOLD TERMINALThe 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.Pin 7 DISCHARGE TERMINAL It connected to the collector of the transistor. As the transistor saturates, capacitor will discharges through the transistor. Whenever, the transistor is cut-off , then the capacitor will charge at a rate which will be determined by the external resistor and capacitor Pin 8 Supply Terminal This is the pin where supply voltage is applied to the terminal with respect to the ground.

The range of the supply voltage is +5v to +18v.Table 1 shows the pin numbers’ functionsB. Transistor BC547 The diagram 3.

2 shows Transistor C. Capacitor (50 µF, 10 nF) The diagram 3.3 shows Capacitor Capacitor used to store energy.D. Battery (5V to 9V) The diagram 3.4 shows BatteryThe range voltage of battery is 5V to 9V.

Thus, the suitable battery use is 9VE. LED The diagram 3.5 shows LEDF.

Resistor ( 220 ? , 100k ?,10k ?) The diagram 3.6 shows ResistorIV. CIRCUIT DESIGN Working ExplanationThis circuit system will cause the LED inside the cabinet to lights up and turn off in specific time. This is cause by the application of monostable mode of IC 555 Timer.

The circuit initial condition at it output is zero which means the door is closed and it is due to the flip-flop in HIGH and both comparators inside the timer is in LOW. When the door is open , the switch will toggle down automatically which then will change IC 555 Timer output state from LOW to HIGH. The push button also will be ground led the input state become zero and the comparator will output .This will cause the Flip-Flop being LOW while the output become HIGH and the LED will lights up.

Whereas, when the door is closed , the LED will also turn off automatically. This is cause by the discharged transistor is turned off and the capacitor started to charge to the R1 until the voltage through the C1 reach 2/3 of the supplied voltage .This then will cause the threshold higher and become one. All of this will bring the circuit to its initial state which then Q bar output become HIGH and will activate the discharge transistor and make the output IC LOW again . DATA SHEET NO I/O DESCRIPTION5 I Controls the threshold and trigger levels.7 I Toggles the output from high to low when volt reaches 2/3 of supply volt.

1 O Ground reference voltage3 O Output driven waveform4 I Negative pulse applied to this pin to disable or reset the timer6 I Responsible for the set state of the flip-flop2 I Responsible for transition of the flip-flop set to reset8 I Supply voltage with respect to GNDREFERENCES1) D Floyd, T. L. (1992). Electronic devices. Columbus, OH: C.

E. Merrill.2) Electronics Components: How the 555 Timer Chip Works. (n.d.).

Retrieved December 2, 2018, from 555 Timer IC-Block Diagram-Working-Pin Out Configuration-Data Sheet. (2018, August 28).

Retrieved December 2, 2018, from Plagiarism Checker. (2018, October 23).

Retrieved from How an LDR (Light Dependent Resistor) Works. (2018, July 12). Retrieved December 2, 2018, from


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