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Biomedical Electronic Engineeering: 555 Timer

Updated August 26, 2022

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Biomedical Electronic Engineeering: 555 Timer essay

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555 timer is one of the most important and useful Integrated Circuit (IC) in the electronic circuit and it is often used in various kind of project. It can works in various function such as oscillator, pulse generation and time delay.

It also can work as flip flop element. It is widely used due to low cost, stable and easy to use. It can operated either as a Monostable, Bistable or Astable to produce a variety of applications. The shoe cabinet is a necessary to any place either home, office and many more. It is the place for storing multiple amount of shoes. Common type of shoe cabinet are made without the built in lamp inside causing it’s hard to find and look inside the cabinet when it is dark.

Therefore, the shoe cabinet need to be modified and have the automatic light. The light will light up when the door is open and it will not light up when the cabinet door is closed. It will have time limitation. The 555 timer IC is one of the important component that will be used to create the circuit. Function of LED lamp :To ease user to find their shoe.

Button is not required to light up the lamp as it is automatic. Precaution for user as some cabinet shoes might have dangerous insects and disturbance. Type of 555 timer operation: Astable mode operated as an electronic oscillator by connecting two external resistors and one capacitor in it specified arrangement. There is no stable output that could cause the waveform to be high and low continuously. Some of its use include LED, logic clocks, and alarms and many more.

Monostable mode: this mode will function as a “single-shot” pulse generator where it arranged one push to on switch, 2 resistors and a capacitor of it specified arrangement. It uses include timer, bounce free switches, frequency divider and many more. Bistable mode could operate as a flip flop which have 2 push on switch and 2 external resistors arranging in it specific arrangement. It is used in digital communication and for reversing supply at regular intervals.

The shoe rack need to have LED light for safety reason. Components and requirements 555 Timer IC Transistor BC547 Capacitor (50 µF, 10 nF) LED and Battery (5-9v) Resistors (220, 100k, 10k ohm) Push button switch Working Explanation Push button switch are installed at the edge of the shoe rack door. The complete circuit of lamp are also installed and attached to the internal of the shoe cabinet.

When someone open the door,the LED inside the shoe cabinet will light up until the specific time stated and it will turn off when the cabinet door is closed. This process is due to operation of the 555 timer (monostable mode). The initial condition at the output of the circuit is 0 due to Q flip flop is high and the comparator at the internal of timer is low. When the door is opened, the push button will connect the circuit.

Then, it will change the output state of 555 timer to high and comparator will have output as one. LED lamp will light up. After the door is closed, the LED will turn off automatically due to the discharging of the transistor. The capacitor will start to charge the R1 until voltage pass through C1 and reached supply voltage. This will cause the threshold to be high .

The circuit will be back to the initial state which the output of the IC to be low again. Thus, we can notice that the amount of time is based on the value of resistor1 and capacitor1.  I Controls the threshold , trigger the levels. 7 I Toggles the output from high to low when volt reaches 2/3 of supplied voltage. 1 O Ground voltage 3 O Output driven waveform 4 I Negative pulse are applied to this pin to disable or reset the timer 6 I Responsible for the flip flop state 2 I Responsible for transition of the flip-flop set to reset 8 I Supply voltage with respect to GND


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  2. H. t. Mechatronics, “How 555 timer works,” 6 February 2018. Online. Available:
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Biomedical Electronic Engineeering: 555 Timer. (2019, Jul 04). Retrieved from