Project Report 555

40 LED

[Using 555 Timer/Oscillator

[The 555 circuit is a flashing bicycle, 20 LEDs will

per second. Each LED is supplied with about 20 mA of current for a total of 220 mA. Uses a NPN

and a PNP transistor.]

40 LED Bicycle Light

Using 555 Timer/Oscillator

B.E Electronics IV

M. Yasir Jamil Khan

M. Raghib Malik

Munir Ahmed Shah

The 555 circuit is a flashing bicycle, 20 LEDs will alternately flash at approximately 4.7 cycles


Bicycle Light

Using 555 Timer/Oscillator]

alternately flash at approximately 4.7 cycles


Introduction to 555 Timer/Oscillator I.C:

“A semiconductor device that controls various modes of on/off states in electrical systems or circuits. The 555 timer is one of the most widely used types of integrated circuits.”

History:

The 555 timer IC was first introduced around 1971 by the

Signetics Corporation as the SE555/NE555 and was called "The IC

Time Machine" and was also the very first and only commercial

timer IC available. It provided circuit designers with a

relatively cheap, stable, and user-friendly integrated circuit

for both monostable and astable applications. Since this device

was first made commercially available, a myriad of novel and

unique circuits have been developed and presented in several

trade, professional, and hobby publications. The past ten years

some manufacturers stopped making these timers because of

competition or other reasons. Yet other companies, like NTE (a

subdivision of Philips) picked up where some left off.

Although these days the CMOS version of this IC, like

the Motorola MC1455, is mostly used, the regular type is still

available, however there have been many improvements and

variations in the circuitry. But all types are pin-for-pin plug

compatible.

In this tutorial the 555 timer is examined in detail along

with its uses, either by itself or in combination with other

solid state devices. This timer uses a maze of transistors,

diodes and resistors and for this complex reason a more

simplified (but accurate) block diagram is used to explain the

internal organizations of the 555.

The 555 is an integrated circuit (chip) implementing a variety

of timer and multivibrator applications. The IC was designed and

invented by Hans R. Camenzind. It was designed in 1970 and

introduced in 1971 by Signetics (later acquired by Philips). The

original name was the SE555/NE555 and was called "The IC Time

Machine". The 555 gets its name from the three 5-kOhm resistors

used in typical early implementations (Reference 1). It is still

in wide use, thanks to its ease of use, low price and good

stability. As of 2003, 1 billion units are manufactured every

year.

The 555 timer is one of the most popular and versatile

integrated circuits ever produced. It includes 23transistors,

2 diodes and 16 resistors on a silicon chip installed in an 8-

pin mini dual-in-line package (DIP-8). The 556 is a 14-pin DIP

that combines two 555s on a single chip. The 558 is a 16-pin DIP

that combines four slightly modified 555s on a single chip (DIS

& THR are connected internally; TR is falling edge sensitive

instead of level sensitive). Also available are ultra-low power

versions of the 555 such as the 7555 and TLC555. The 7555

requires slightly different wiring using fewer external

components and less power.

The 555 has three operating modes:

� Monostable mode: in this mode, the 555 functions as a "one-

shot". Applications include timers, missing pulse

detection, bounce free switches, touch switches, Frequency

Divider, Capacitance Measurement, Pulse Width

Modulation (PWM) etc

� Astable - Free Running mode: the 555 can operate as

an oscillator. Uses include LED and lamp flashers, pulse

generation, logic clocks, tone generation, security

alarms, pulse position modulation, etc.

� Bistable mode or Schmitt trigger: the 555 can operate as

a flip-flop, if the DIS pin is not connected and no

capacitor is used. Uses include bounce free latched

switches, etc.

Inside a 555 Timer/Oscillator:

Inside the 555 timer,

are the equivalent of

over 20 transistors, 15

resistors, and 2

diodes, depending of

the manufacturer.

The equivalent

circuit, in block

diagram, providing

the functions of

control, triggering,

level sensing or

comparison,

discharge, and power

output. Some of the

more attractive

features of the 555

timer are: Supply

voltage between 4.5

and 18 volt, supply

current 3 to 6 mA,

and a Rise/Fall time of

100n Sec. It can also

withstand quite a bit

of abuse. The

Threshold current

determine the

maximum value of Ra

The connection of the pins are as follows:

Nr. Name Purpose

1 GND Ground, low level (0V)

2 TR A short pulse high → low on the trigger starts

the timer

3 Q During a timing interval, the output stays at +VCC

4 R A timing interval can be interrupted by applying

a reset pulse to low (0V)

5 CV Control voltage allows access to the internal

voltage divider (2/3 VCC)

6 THR The threshold at which the interval ends (it ends

if U.thr → 2/3 VCC)

7 DIS Connected to a capacitor whose discharge time

will influence the timing interval

8 V+,

VCC

The positive supply voltage which must be between

3 and 15 V

Transistors:

1) 2N2219A (high speed switches)

The 2N2219A and 2N2222A are silicon planar Epitaxial NPN

transistors in Jedec TO-39 (for 2N2219A) and in Jedec TO-18 (for2n2222a) Metal case. They are designed for high speed

Switching application at collector current up to 500ma, and

feature useful current gain over a Wide range of collector current, low leakage currents and low saturation voltage.

2) 2N2907A (General Purpose Amplifiers Andswitches):

The 2N2905A and 2N2907A are silicon planar epitaxial PNP

transistors in JedecTO-39 (for 2N2905A) and in JedecTO-18

(for 2N2907A) metal case. They are designed for high speed

saturated switching and general purpose applications.

Light-emitting diodeA light-emitting-

that emits light when an electric current is applied

in the forward direction of the device, as in the

simple LED circuit. The effect is a form of

electroluminescence where incoherent and narrow

spectrum light is emitted from the p

solid state material.

LEDs are widely used as indicator lights on

electronic devices and increasingly in higher power

applications such as flashlights and area lighting.

An LED is usually a small area (less than 1 m

light source, often with optics added directly on top

of the chip to shape its radiation pattern and assist

in reflection. The color of the emitted light depends

on the composition and condition of the

semiconducting material used, and can be infrared,

visible, or ultraviolet. Besides lighting,

interesting applications include using UV

sterilization of water and disinfection of devices,

and as a grow light to enhance photosynthesis in

plants.

emitting diode: -diode (LED) is a semiconductor diode



rcuit. The effect is a form of

electroluminescence where incoherent and narrow

spectrum light is emitted from the p-n ju

solid state material.




An LED is usually a small area (less than 1 m




on the composition and condition of the



interesting applications include using UV



Schematic Symbol of LED

semiconductor diode



rcuit. The effect is a form of

electroluminescence where incoherent and narrow-

n junction in a




An LED is usually a small area (less than 1 mm2)






interesting applications include using UV-LEDs for



Schematic Symbol of LED

Working:

The 555 circuit below is a flashing bicycle light powered with four C, D or AA cells

(6 volts).

Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second

using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time

intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104

milliseconds (T2 lower LEDs). Two transistors are used to provide additional

current beyond the 200 mA limit of the 555 timer. A single LED is placed in series

with the base of the PNP transistor so that the lower 20 LEDs turn off when the

555 output goes high during the T1

Schematic Diagram

40 LED Bicycle Light





wer LEDs). Two transistors are used to provide additional



555 output goes high during the T1 time interval. The high output level of the 555





wer LEDs). Two transistors are used to provide additional



time interval. The high output level of the 555

timer is 1.7 volts less than the supply voltage. Adding the LED increases the

forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7

volt difference from supply to the output is insufficient to turn on the transistor.

Each LED is supplied with about 20 mA of current for a total of 220 mA.

The circuit should work with additional LEDs up to about 40 for each group, or 81

totals. The circuit will also work with fewer LEDs so it could be assembled and

tested with just 5 LEDs (two groups of two plus one) before adding the others.

Components Details:

Components that are used in the circuit are as follow:

Sr. No. Name Quantity Substitute

1 555 Timer/Oscillator 01 *****

2 2N3053 (NPN) 01 2N2219A

3 2N2905 (PNP) 01 2N2907A

4 Resistor 4.7 K ohm 01 *****

5 Resistor 150 K ohm 01 *****

6 Resistor 220 ohm 01 *****



9 Capacitor 1 uF 01 *****

10 Capacitor 1 F 01 *****

11 Led 40 01 *****

Output Wave Form/Graph:

The 555 timer I.C generating the alternatively the D.C signals of approximately 4.7

cycles per second.

When the set one of led is on other remain off.

The

Data Sheets

of Used

Components

Resources:

http://www.uoguelph.ca/~antoon/gadgets/555/555.html

http://www.national.com/pf/LM/LM555.html

http://www.doctronics.co.uk/555.htm

http://www.doctronics.co.uk/safety_lights.html#limiting

http://en.wikipedia.org/wiki/Wikipedia

http://www.kpsec.freeuk.com/555timer.htm

http://home.cogeco.ca/~rpaisley4/LM555.html#15

http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm

http://pr.radom.net/~pgolabek/materialy/Elektronika/Dodatki/555/www.ee.ed.ac.uk/~kap/hard/555/a

plications.html

Documents

Project Report 555