RIZAL TECHNOLOGICAL UNIVERSITY

COLLEGE OF ENGINEERING, ARCHITECTURE AND TECHNOLOGY

Boni Avenue, City of Mandaluyong

DEPARTMENT OF ELECTRONICS AND COMMUNICATIONS

ENGINEERING AND TECHNOLOGY
First Semester, School Year 2021-2022

SEGRAGATION OF TASKS TO THE GROUP MEMBERS FOR THE VIDEO

PRESENTATION
ECE03 | Electronics 3: Electronic Systems and Design

Submitted by:
GROUP 1

LEADER:
ALICPALA, IRISH ANNE T.

MEMBERS:
ABADILLA, SOPHIA JONAH
ALMIÑE, ELWIN L.
ARABIS, KRISTIAN RIKKI A.
ASIGNACION, CHRISTIAN L.

Submitted to:
ENGR. ODILON B. YANGCO
INTRODUCTION OF LM555

The LM555 timer chip is extremely robust and stable 8-pin device that can
be operated either as a very accurate Monostable, Bistable or Astable Multivibrator
to produce a variety of applications such as one-shot or delay timers, pulse
generation, LED and lamp flashers, alarms and tone generation, logic clocks,
frequency division, power supplies and converters etc, in fact any circuit that
requires some form of time control as the list is endless.

Dissection of LM555 1|Page

 THE DIFFERENT PARTS OF LM555 AND THEIR FUNCTIONS

• OUTER PART

LM555

PIN NUMBER PIN NAME PIN FUNCTION

1 GROUND Pin 1 connects the 555 timer chip to ground.
Pin 2 is the trigger pin. It works like a starter pistol
to start the 555 timer running. The trigger is an active
low trigger, which means that the timer starts when
2 TRIGGER voltage on pin 2 drops to below 1/3 of the supply
voltage. When the 555 is triggered via pin 2, the
output on pin 3 goes high.
Pin 3 is the output pin. 555 timer's output is digital
in nature. It is either high or low. The output is either
low, which is very close to 0V, or high, which is close
3 OUTPUT to the supply voltage that's placed on pin 8.

The output pin is where you would connect the load

that you want the 555 timer to power. This may be
an LED, in the case of a 555 timer LED flasher circuit.

Dissection of LM555 2|Page

 Pin 4 is the reset pin. This pin can be used to restart
the 555 timer's timing operation.

This is an active low input, just like the trigger input.

4 RESET Thus, pin 4 must be connected to the supply voltage
of the 555 timer to operate. If it is momentarily
grounded, the 555 timer's operation is interrupted
and won't start again until it's triggered again via pin
2.
Pin 5 is the control pin. In most 555 timer circuits,
this pin is simply connected to ground, usually
through a small capacitor, about 0.01 µF capacitor.
This capacitor serves to level out any fluctuations in
the power supply voltage that might affect the
operation of the timer.
5 CONTROL
VOLTAGE Some circuits (though rare) do use a resistor
between the control pin and Vcc to apply a small
voltage to pin 5. This voltage alters the threshold
voltage, which in turn changes the timing interval.
Most circuits do not use this capability, though.
Pin 6 is the threshold pin. The purpose of this pin is
to monitor the voltage across the capacitor that's
6 THRESHOLD discharged by pin 7. When this voltage reaches 2/3
of the supply voltage (Vcc), the timing cycle ends,
and the output on pin 3 goes low.
Pin 7 is the discharge pin. This pin is used to
discharge an external capacitor that works in
7 DISCHARGE conjunction with a resistor to control the timing
interval. In most circuits, pin 7 is connected to the

Dissection of LM555 3|Page

 supply voltage through a resistor and to ground
through a capacitor.
Pin 8 is connected to the positive power supply
voltage.

555 timer ICs need DC voltage in order to operate.

This is the pin which connects to the DC voltage to
8 VCC power the 555 chip.

The voltage must be at least 4.5V and no greater

than 15V. It's common to run 555 timer circuits using
4 AA or AAA batteries for 6V or a single 9V battery.

• INNER PART

Dissection of LM555 4|Page

 NAME FUNCTION
When a negative ( 0V ) pulse is applied to the trigger input (pin 2)
of the Monostable configured 555 Timer oscillator, the internal
COMPARATOR comparator, (comparator No1) detects this input and “sets” the
state of the flip-flop, changing the output from a “LOW” state to
a “HIGH” state.
Voltage dividers are used for adjusting the level of a signal, for
VOLTAGE bias of active devices in amplifiers, and for measurement of
DIVIDER voltages. A Wheatstone bridge and a multimeter both include
voltage dividers.
The output from the flip-flop is used to control a high current
FLIP FLOP output switching stage to drive the connected load producing
either a “HIGH” or “LOW” voltage level at the output pin.

Dissection of LM555 5|Page

 It is used to discharge the timing capacitor when the voltage
reaches two-thirds the supply voltage set by comparator 1,
DISCHARGE governed by the 3 x 5k resistors in the potential divider. This can
TRANSISTOR be discharged to one-third the supply voltage, so can begin
another cycle of charging.
OUTPUT DRIVER Output drivers are designed to drive signals between high and
low voltage levels

ADDITIONAL INFORMATIONS

USES / FUNCTIONS

• The LM555 timer can be used for basic timing functions, create warning
lights that flash on and off, produce musical notes of varying frequencies,
and even control the control position of a servo motor.

You can use the 555 chips for basic timing functions, such as turning a light
on for a certain length of time, or you can use it to create a warning light that
flashes on and off. You can use it to produce musical notes of a particular
frequency, or you can use it to control positioning of a servo device.

APPLICATIONS

The LM555 timer can be used a various configurations, but the most commonly
used configuration is in monostable mode. A typical application for the LM555
timer in monostable mode is to turn on an LED for a specific time duration. A
pushbutton is used as the trigger to output a high pulse when trigger pin is pulsed
low. This simple application can be modified to fit any application requirement.

• LM555 timer is most important integrated circuit (chip) used widely in digital
electronics. Some common uses and application of 555 timer IC are as
follow:

Dissection of LM555 6|Page

 • PWM (Pulse Width Modulation) & PPM (Pulse Position Modulation)
• Duty Cycle Oscillator
• Lamp Dimmer
• To provide Accurate time delays
• As a flip-flop element
• Digital logic probes
• Analog frequency meters
• Quad Timer applications
• Pulse, Waveform, and square wave generation
• Stepped tone & tone burst generator & linear ramp generation
• Tachometers & temperature measurement
• It can be used as monostable multivibrator and astable multivibrator
• DC to DC Converters
• DC Voltage Regulators
• Voltage to Frequency Converter
• Frequency Divider
• Schmitt trigger
• Cable tester
• Pulse detector
• Wiper speed control
• Timer Switch
• Time delay generation, precision timing and sequential timing
• The 555 Timer IC are widely used in most of interesting electronic circuits
and project like Traffic Light Circuit using 555 Timer, LED Flashing circuits,
police siren, LED dice, Music Box, Metal detector, Joystick and game
paddles, & low cost line receiver, Clap switch activated circuit and lots of
other projects and circuits designs.

Dissection of LM555 7|Page

FEATURES DESCRIPTION OF LM555

• Direct Replacement For Se555/Ne555

The LM555 timer is a direct replacement for SE555 and NE555. It is pin-to-pin
compatible so that no schematic or layout changes are necessary. The LM555
come in an 8-pin PDIP, SOIC, and VSSOP package.

• Timing From Microseconds Through Hours

The LM555 has the ability to have timing parameters from the microseconds
range to hours. The time delay of the system can be determined by the time
constant of the R and C value used for either the monostable or astable
configuration. A nomograph is available for easy determination of R and C
values for various time delays.

• Operates in Both Astable and Monostable Mode

The LM555 can operate in both astable and monostable mode depending on the
application requirements.

• Monostable mode: The LM555 timer acts as a “one-shot” pulse generator.

The pulse beings when the LM555 timer receives a signal at the trigger input
that falls below a 1/3 of the voltage supply. The width of the output pulse is
determined by the time constant of an RC network. The output pulse ends when
the voltage on the capacitor equals 2/3 of the supply voltage. The output pulse
width can be extended or shortened depending on the application by adjusting
the R and C values.

• Astable (free-running) mode:

The LM555 timer can operate as an oscillator and puts out a continuous stream
of rectangular pulses having a specified frequency. The frequency of the pulse
stream depends on the values of RA, RB, and C.

Dissection of LM555 8|Page

 PRESENTER IN LM555
NAME TOPIC
ABADILLA VOLTAGE DIVIDER
ALICPALA FLIP-FLOP
ALMIÑE DISCHARGE TRANSISTOR
ARABIS OUTPUT DRIVER
ASIGNACION COMPARATOR

Prepared by:
ABADILLA, SOPHIA JONAH
ALICPALA, IRISH ANNE T.
ALMIÑE, ELWIN L.
ARABIS, KRISTIAN RIKKI A.
ASIGNACION, CHRISTIAN L.

Approved by:

ENGR. ODILON B. YANGCO

Dissection of LM555 9|Page