BYM 501 E Fundamentals of Biomedical Engineering Saman

BYM 501 E Fundamentals of Biomedical Engineering Saman ahdi rezaeieh M. Sc student of BME in itu Advisor: Inci Fatma Cilesiz

Context ü Kind of timers ü Type of signals ü Duty cycle ü General information about Ic 555 timer ü The usage of ic 555 in bme

Kind of timers A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass. Timers can be mechanical, electronic (quartz), or even software as all modern computers include digital timers of one kind or another. When the set period expires some timers simply indicate so (e. g. , by an audible signal), while others operate electrical switches, such as a time switch, which cuts electrical power.

Analog and digital signals Analog and Digital are the different forms of signals. Signals are used to carry information from one device to another. Analog signal is a continuous wave that keeps on changing over a time period. Digital signal is discrete in nature. The fundamental difference between analog and digital signal is that analog signal is represented by the sine waves whereas, the digital signal is represented by square waves.

Duty Cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. Thus, a 60% duty cycle means the signal is on 60% of the time but off 40% of the time.

General information about Ic 555 timer What is a 555 timer IC? 555 timer is an integrated circuit which contains 8 pins and the description of each pin is given in the pin description. This timer is used in the pulse generation, oscillators and in different timer circuits. The 555 timer produces time delays in the oscillator, also in flip flop elements and the 555 timer contains three modes which are Astable, Bistable and Monostable modes. The following diagram shows the 555 timer integrated circuit.

Pin description of Ic 555 timer The 555 timer consists of 8 pins and these pins contain different types of functions.

Pin description of Ic 555 timer Pin 1 It is the ground pin directly connected to the negative rail. It should not be connected using a resistor, because all the semiconductors inside the IC will heat up due to stray voltage accumulating in it. Pin 2 It is the Trigger pin to activate the IC’s timing cycle. It is generally low signal pin and the timer is triggered when voltage on this pin is below one third of the supply voltage. The trigger pin is connected to the Inverting input of the comparator inside the IC and accepts negative signals. The current required for triggering is 0. 5 u. A for a period of 0. 1 u. S.

Pin description of Ic 555 timer Pin 3 It is the output pin. When the IC triggers via pin 2, the output pin goes high depending on the duration of the timing cycle. It can either sink or source current which is at maximum 200 m. A. Pin 4 It is the reset pin. It should be connected to the positive rail to work the IC properly. When this pin is grounded, the IC will stop working. The reset voltage required for this pin should be 0. 7 volts at a current of 0. 1 m. A.

Pin description of Ic 555 timer Pin 5 Control pin – The 2/3 supply voltage point on the terminal voltage divider is brought to the control pin. It requires to be connected to an external DC signal to modify the timing cycle. When not in use, it should be connected to the ground through a 0. 01 u. F capacitor; otherwise the IC will show erratic responses. Pin 6 It is the Threshold pin. The timing cycle is completed when voltage on this pin is equal to or greater than two-third of Vcc. It is connected to the non inverting input of the upper comparator so that it accepts the positive going pulse to complete the timing cycle.

Pin description of Ic 555 timer Pin 7 Discharge pin. It provides a discharge path for the timing capacitor through the collector of the NPN transistor, to which it is connected. The maximum allowable discharging current should be less than 50 m. A otherwise the transistor may damage. It can be also used as an open collector output. Pin 8 It is positive rail connected pin which is connected to positive terminal of the power supply. It is also known as Vcc. IC 555 works in a wide range of voltage from 5 V to 18 V DC where as the CMOS version 7555 works with 3 Volts.

Pin description of Ic 555 timer

Ic 555 in devices An oscilloscope is a laboratory instrument commonly used to display and analyze the waveform of electronic signals. In effect, the device draws a graph of the instantaneous signal voltage as a function of time. A typical oscilloscope can display alternating current (AC) or pulsating direct current (DC) waveforms having a frequency as low as approximately 1 hertz (Hz) or as high as several megahertz (MHz)

references Ø Ø https: //whatis. techtarget. com/definition/oscilloscope https: //www. edgefx. in/555 -timer-ic-introduction-and-working-with-operating-modes/ https: //electronicsforu. com/electronics-projects/555 -timer-circuits https: //www. elprocus. com/555 -timer-pin-description-applications/

Thanks For Your attention Saman ahdi rezaeieh