Project 01 Building simple Astable using 555 IC # Student ID Student Name Grade (10) 1 Delivery Date 1. يتم تسليم المشروع في خالل أسبوعين من تاريخ عرضة و يتم حذف درجتان و نصف من المشروع عن كل أسبوع تأخير 2. يتم تسليم المشروع لمعيد المقرر مباشرة -1 / 19 -
Introduction A 555 Timer is an 8 pin mini dual-in-line package IC. The 555 IC is capable of producing accurate time delays and/ or oscillations. Introduced in 1972 by SigNetics.(Signal Networks Electronics) The 555 is still in widespread use,thanks to its ease of use, low price, and good stability. -2 / 19 -
Features High Current Drive Capability (200mA) Adjustable Duty Cycle Temperature Stability of 0.005%/ C Timing From μsec to Hours Turn off Time Less Than 2μSec Monostable and Astable operation Ability to operate from a wide range of supply voltages Trigger and reset inputs are logic compatible -3 / 19 -
What is inside 555 A functional block diagram of 555 timer is given below. The device consists of two comparators,2 transistors, a flip-flop and buffered outputs stage. The reference voltages for the two comparators inside the 555 are produced across a voltage divider consisting of three equal resistors of 5K ohms each. Look at the given block diagram of the IC, to see that there are three resistors of 5kohm each connected in series. These three resistors produce 1/3 and 2/3 voltage levels for controlling the action of trigger and threshold comparators inside the IC. Due to this arrangement of the three resistors, the IC has a typical code number as IC555. The threshold comparator is referenced at 2/3 Vcc and the trigger comparator is referenced at 1/3Vcc. The two comparators control the flip-flop which, in turn, controls the state of the output i.e. either ON or OFF states. -4 / 19 -
Pin configuration of IC 555 : Pin-1, GROUND: It is the GROUND PIN of the IC. The negative terminal of DC power supply or battery is connected to this pin. Note that this pin should be connected directly to ground and NOT through any resistor or capacitor. If done so, the IC will not function properly and may heat up and get damaged. This happens because all the semiconductor blocks inside the IC will be raised by certain amount of stray voltage and will damage the IC.IC 555 Pin-2, TRIGGER It is known as TRIGGER PIN. As the name suggests in triggers i.e. starts the timing cycle of the IC. It is connected to the inverting input terminal of trigger comparator inside the IC. It triggers when the voltage at this pin LESS THAN 1/3 of the supply voltage (Vcc). The triggering circuit inside the IC is very sensitive and may be accidently activated due to surrounding noise. To avoid this, the pin is always connected to a pull-up resistor (10k-ohm), if this pin is used separately. Pin-3, OUTPUT This is the OUTPUT PIN of the IC. It can SINK or SOURCE a maximum current of 200mA. Sinking the current means, when the output of the IC is at logic-0 state i.e. LOW and so it can absorb current into its output. Similarly sourcing the current means, when the output of the IC is at logic-1 i.e. HIGH and so it can give out current from its output. Pin-4, RESET It is the RESET PIN of the IC. When it is connected to positive terminal of battery, the IC works normally. However, when it is grounded (either directly or through a maximum of 100k-ohm resistor), the IC stops its working completely and its timing cycle stops.however in general applications, this pin is always connected to positive terminal so that the IC works normally. Pin-5, C. VOLTAGE This is known as the CONTROL VOLTAGE pin. The 2/3 of supply voltage point on the terminal voltage divider is brought out to pin-5, known as the control terminal of the IC. The timing cycle can be modified by applying external DC control voltageto this pin. This allows manual or electronic remote controlling of the time interval of the IC. But if you are NOT using this pin for any such purpose, then this pin MUST BE GROUNDED THROUGH A CAPACITOR OF 0.01uF. -5 / 19 -
This prevents the time interval from being affected by picking up of stray AC or RF noise from the surrounding. Pin-6, THRESHOLD This is known as the THRESHOLD PIN. It finalizes the timing cycle of the IC, when its voltage is equal to or greater than 2/3Vcc, the output is at logic-0 state.note that the typical value of threshold current is 0.1mA, just like the RESET PIN. The time width of this pulse should be greater than or equal to 0.1uS. Pin-7, DISCHARGE It is known as DISCHARGE PIN. It discharges the external capacitor into itself, but when fully charged! It is connected to the collector of an NPN transistor inside the IC. Due to this, the discharging current going into this pin MUST NOT EXCEED 50mA, otherwise the internal transistor may get damaged. Pin-8, +Vcc It is known as the +ve supply terminal of the IC. The battery voltage connected across this pin and ground pin SHOULD NOT EXCEED 18V. Generally the range of operating voltage of the IC is 3V 18V. -6 / 19 -
Modes of operations 1. Monostable Operation In this mode, the timer generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's internal flip-flop turns the discharging Transistor off and causes the timer output to become high by charging the external capacitor C1and setting the flip-flop output at the same time. -7 / 19 -
2. Astable Operation In astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multivibrator. When the timer output is high, its internal discharging Transistor turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C. When the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high, resetting the F/F and causing the timer output to become low. -8 / 19 -
The high period The low period The total period is The frequency is T1 = 0.7 (R1 + R2) Ct T2 = 0.7 (R2) Ct T=0.7(R1+2 R2) Ct ( ) -9 / 19 -
Components list # Q item link image 1 1 555 http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=609 2 3 Resistor = 10K ohm (R1, R2) http://ram-eshop.com/oscmax/catalog/product_info.ph p?cpath=31_46_69&products_id=383 3 1 Capacitor = 10 uf http://ram-eshop.com/oscmax/catalog/product_info.ph p?cpath=30_88&products_id=485 4 1 Capacitor = 100 uf http://ram-eshop.com/oscmax/catalog/product_info.php?p roducts_id=504-10 / 19 -
5 2 Led 5mm http://ram-eshop.com/oscmax/catalog/product_info.ph p?cpath=60&products_id=227 6 2 Resistor = 1K R3 http://ram-eshop.com/oscmax/catalog/product_info.ph p?cpath=31_46_69&products_id=342 7 1 Bread board http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=164-11 / 19 -
8 1 Power supply http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=1394 or http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=1106 9 1 Power socket 2 bead board http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=1203-12 / 19 -
10 1 wires http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=221 or http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=3183 11 1 press http://ram-eshop.com/oscmax/catalog/product_info.ph p?products_id=1568-13 / 19 -
Introduction to work with Breadboard The purpose of the breadboard is to make quick electrical connections between components- like resistors, LEDs, capacitors, etc- so that you can test your circuit before permanently soldering it together. Breadboards have many small sockets on them, and some groups of sockets are electrically connected to each other. On the underside of the board there are many small metal strips which physically connect certain groups of sockets together and allow electricity to flow freely between them. These strips are probably not visible on the underside of your breadboard, but the third picture shows how they are organized. Breadboards are usually divided into four sections, two outer sections and two inner sections. Each row of five sockets in the inner sections are electrically connected to each other (see the green lines in figure 3). The two outer sections of the breadboard are usually used exclusively for power. On many breadboards these sockets will be labeled with colors denoting positive voltage (usually red) and ground (black or blue). It is important to note that on many breadboards the power lines only run half the length of the board (as indicated in figure 3). You will need to run a wire between these two sections to send power to from one end to the other. There is nothing special about the outer sections of the breadboard that makes particularly suitable for power other than that they run most of the length of the board, but if you choose to use these rows for other -14 / 19 -
things you may confuse others or even yourself, so it is good practice to use these for power only. The first thing to do is send power to the breadboard. Breadboards do not have their own power supply. Some breadboards come with a power supply attached, but it is usually not connected directly to the power lines on the breadboard. Power supplies come in many shapes and sizes, you may have to dial in the voltage or your power supply may only let you chose from one or a few types voltage levels. We will be using 12V DC power. This means that you will make two connections to your power supply, +12 and ground. Remember, many breadboards separate each of the two power rows into two sections (electricity cannot flow across the center of the board), so you'll need to connect these -15 / 19 -
groups with jumper cables to ensure that power is being sent across the length of the board (above figure). Now the breadboard is powered. Convince yourself by using a multimeter to measure the voltage of any of the sockets in the power lines of the board. Your first circuit will turn an LED on. The circuit diagram is given in figure; it includes an LED and a resistor connected in series to power The resistor is there to prevent too much current from going through the LED; we call it a "current-limiting resistor." If you connect an LED to your 12V power supply directly it will most likely burn out, this may be accompanied by a cracking sound, a smell, smoke, or even a small explosion, so be careful! I'm using a 1/4 watt 1Kohm resistor for my current limiting resistor, if you know the specs of your LED you can find the best resistor value for your circuit using an online LED calculator. Using too much resistance in this circuit will never damage the LED, it will just glow slightly dimmer. -16 / 19 -
Electric current always runs from high voltage to ground in a circuit. Some components only work when current flows through them in one direction (and they may even be damaged by wiring them backwards). As the first images indicate, LEDs must be wired so that current flows from the anode (the longer lead) to the cathode (the shorter lead). Resistors do not have directionality, this mean that you can flip a resistor around in a circuit and it will behave exactly the same. -connect the anode of the LED to +12V and the cathode to a row of pins in the middle section of the breadboard. -connect one resistor lead to ground and the other lead to a pin in the same row as the LED cathode. -connect power to the board- the LED should light up. As you can see, connecting the LED and the resistor to the same row of sockets on the breadboard created an electrical connection between these two components. -17 / 19 -
Implementing Astable on a bread board -18 / 19 -
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