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Our 4th Semester Project Report
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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
per second. Each LED is supplied with about 20 mA of current for a total of 220 mA. Uses a NPN
Bicycle Light
Using 555 Timer/Oscillator]
alternately flash at approximately 4.7 cycles
per second. Each LED is supplied with about 20 mA of current for a total of 220 mA. Uses a NPN
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
that emits light when an electric current is applied
in the forward direction of the device, as in the
rcuit. The effect is a form of
electroluminescence where incoherent and narrow
spectrum light is emitted from the p-n ju
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
Schematic Symbol of LED
semiconductor diode
that emits light when an electric current is applied
in the forward direction of the device, as in the
rcuit. The effect is a form of
electroluminescence where incoherent and narrow-
n junction in a
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 mm2)
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
semiconducting material used, and can be infrared,
visible, or ultraviolet. Besides lighting,
interesting applications include using UV-LEDs for
sterilization of water and disinfection of devices,
and as a grow light to enhance photosynthesis in
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
The 555 circuit below is a flashing bicycle light powered with four C, D or AA cells
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
wer 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 time interval. The high output level of the 555
The 555 circuit below is a flashing bicycle light powered with four C, D or AA cells
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
wer 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
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 *****
7 Resistor 160 ohm 01 *****
8 Resistor 100 ohm 20 *****
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
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