An embedded system is a dedicated computer system that performs specific tasks. An important application of embedded systems is anti-lock braking systems (ABS) in automobiles. ABS uses sensors and electronic control modules to monitor wheel speed and automatically modulate brake pressure to prevent wheel lockup and maintain steering control during emergency braking. By preventing skidding, ABS can help drivers stop more safely and shorten stopping distances on wet or slippery surfaces compared to standard brakes. ABS works by pulsing the brakes rapidly when it detects a wheel is about to lock up, which allows the wheel to continue turning and maintaining traction with the road.

1. EMBEDDED SYSTEMS
ANTI-LOCK BRAKING SYSTEM
ABSTRACT:
Embedded system is the recent emerging
technology in the field of electronics. An
important application of embedded system
is Anti-lock brake system (ABS) in
automobiles.
Anti-lock Braking systems were developed
to reduce skidding and maintain steering
control when brakes are used in an
emergency situation. Anti-lock Brakes are
essentially an enhanced or improved version
of ordinary brakes. Simply put, the antilock
brake system is designed to prevent the
brakes from locking up and skidding when
braking hard or when braking on wet or
slick surfaces.
ABS brakes work by automatically
actuating the brakes on and off during
emergency stops. They are effective in
helping drivers avoid accidents. In certain
situations, ABS brakes can help to shorten
stopping distances. This adds a significant
margin of safety for everyday driving by
preventing dangerous skids and allowing the
driver to maintain steering control while
trying to stop. This paper reveals an
overview of embedded systems and its
application in automobiles.
INTRODUCTION
An embedded system performs one or a few
pre-defined tasks, usually with very specific
requirements. Since the system is dedicated
to specific tasks, design engineers can
optimize it, reducing the size and cost of the
product. Embedded systems are often mass-
produced, benefiting from economies of
scale.
In terms of complexity embedded systems
can range from very simple with a single
microcontroller chip, to very complex with
multiple units, peripherals and networks
mounted inside a large chassis or enclosure.

2. CHARACTERISTICS OF EMBEDDED
SYSTEM
 Some have real-time performance
constraints that must be met, for
reason such as safety and usability.
 Some may have low or no
performance requirements, allowing
the system hardware to be simplified
to reduce costs.
 An embedded system is not always a
separate block - very often it is
physically built-in to the device it is
controlling.
 It often runs with limited computer
hardware resources.
CPU PLATFORM
Embedded processors can be broken into
two distinct categories: microprocessors
(µP) and microcontrollers (µC).
Microcontrollers have built-in peripherals
on the chip, reducing size of the system.
DEBUGGING
Embedded Debugging may be performed at
different levels, depending on the facilities
available, ranging from assembly- or
source-level debugging with an in-circuit
emulator or in-circuit debugger.
RELIABILITY
Embedded systems often reside in machines
that are expected to run continuously for
years without errors and in some cases
recover by themselves if an error occurs.
Therefore the software is usually developed
and tested more carefully than that for
personal computers, and unreliable
mechanical moving parts such as disk
drives, switches or buttons are avoided.
APPLICATIONS
 Automatic teller machines (atms).
 Avionics, such as inertial guidance
systems, flight control
hardware/software.

3.  Cellular telephones and telephone
switches.
 Engine controllers and antilock
brake controllers for automobiles.
 Handheld calculators, computers,
medical equipment.
 Household appliances.
 Computer peripherals such as routers
and printers.
ANTI-LOCK BRAKING SYSTEM
Antilock braking systems (ABSs) are
electronic systems that monitor and control
wheel slip during vehicle braking. ABSs can
improve vehicle control during braking, and
reduce stopping distances on slippery road
surfaces by limiting wheel slip and
minimizing lockup.
Antilock Brakes system is designed to
prevent the brakes from locking up and
skidding when braking hard or when
braking on wet or slick surfaces. Antilock
brakes do not necessarily reduce the
stopping distance, and in fact may actually
increase stopping slightly on dry pavement.
But on wet or slick pavement, antilock
brakes may reduce the stopping distance up
to 25% or more, which could be the
difference between a safe stop and an
accident.
A tire that is just on the verge of slipping
(10 to 20% slippage) produces more friction
with respect to the road than one, which is
locked, and skidding (100% slippage). Once
traction is lost, friction is reduced, the tire
skids and the vehicle takes longer to stop.
COMPONENTS
The anti-lock brake controller is also known
as the CAB (Controller Anti-lock Brake).
A typical ABS is composed of
 A central electronic unit.
 Four speed sensors (one for each
wheel).
 Two or more hydraulic valves on the
brake circuit.

4.  ABS malfunction indicator lamp.
WHEEL SPEED SENSOR
The wheel speed sensors (WSS) consist of a
magnetic pickup and a toothed sensor ring.
As the wheel turns, teeth on the sensor ring
move through the pickup magnetic field.
This reverses the polarity of the magnetic
field and induces an alternating current
(AC) voltage in the pickup windings. The
number of voltage pulses per second that are
induced in the pickup changes in direct
proportion to wheel speed. So as speed
increases, the frequency and amplitude of
the wheel speed sensor goes up.
MODULATOR VALVES
ABS modulator valves regulate the air
pressure to the brakes during ABS action.
When not receiving commands from the
ECU, the modulator valve allows air to flow
freely and has no effect on the brake
pressure.
The ECU commands the modulator value
to either:
• Change the air pressure to the brake
chamber, or

5. • Hold the existing pressure.
The modulator valve usually has three ports:
• Supply port: It receives air
from a quick release or relay
valve.
• Delivery port: It sends air to the
brake chambers.
• Exhaust port: It vents air from
the brake chamber(s).
Typically, when an ECU detects impending
wheel lockup, it activates the solenoids to
close the supply port and open the exhaust
port. When enough air is vented to prevent
wheel lockup, the exhaust valve will close.
ELECTRONIC CONTROL UNIT
The ABS electronic control module is a
microprocessor that functions like the
engine control computer. It uses input from
its sensors to regulate hydraulic pressure
during braking to prevent wheel lockup.
The key inputs for the ABS control module
come from the wheel speed sensors and a
brake pedal switch. The switch signals the
control module when the brakes are being
applied, which causes it to go from a
"standby" mode to an active mode.
When ABS braking is needed, the control
module kicks into action and orders the
hydraulic unit to modulate brake pressure as
needed. On systems that have a pump, it
also energizes the pump and relay. Like any
other electronic control module, the ABS
module is vulnerable to damage caused by
electrical overloads, impacts and extreme
temperatures.
MALFUNCTION INDICATOR LAMP
(MIL)
 Illuminated in key position 2
 Goes out with engine running
 Illuminated when a fault is present
 Will indicate low available voltage
(< 10.5 V)

6.  Flickering off and on while engine is
running indicates a voltage supply
problem
WORKING
The electronic unit constantly monitors the
rotation speed of each wheel. When it
senses that any number of wheels are
rotating considerably slower than the others
it moves the valves to decrease the pressure
on the braking circuit, effectively reducing
the braking force on that wheel. Wheel(s)
then turn faster and when they turn too fast,
the force is reapplied. This process is
repeated continuously, and this causes the
characteristic pulsing feel through the brake
pedal.
The sensors can become contaminated with
metallic dust and fail to detect wheel slip;
this is not always picked up by the internal
ABS controller diagnostic.
ABS CONTROL MODE
PRESSURE HOLD
Vehicle speed signal indicates wheel is
about to lock.
Pressure still applied, but can’t increase
because ABS control module has activated
value y8.
PRESSURE RELEASE
To reduce pressure at locking wheels (the
wheel that has stopped spinning):
ABS control module:
• Activates return pump
• Activates Valve y8 so no more
pressure can be applied

7. • Activates valve y9 so pressure at
brake can be reduced
These valves can be pulsed very rapidly.
You can feel this stage of operation through
the brake pedal.
TRACTION CONTROL
The ABS equipment may also be used to
implement traction control on acceleration
of the vehicle. If, when accelerating, the tire
loses traction with the ground, the ABS
controller can detect the situation and take
suitable action so that traction is regained.
Manufacturers often offer this as a
separately priced option even though the
infrastructure is largely shared with ABS.
More sophisticated versions of this can also
control throttle levels and brakes
simultaneously.
DRIVING WITH ABS
When vehicle first exceeds 5mph after a
start-up, a self-test is performed. With foot
on brake pedal, a pulsation will be felt.
Driver applies brakes:
– If wheels do not approach lock-up, then
ABS is not activated and brakes function as
in a non-ABS vehicle.
– As vehicle is braked, ABS may be able to
prevent wheel lock-up by simply holding
the brake fluid pressure from going any
higher. The driver would not sense this
stage of control.
– If driver feels brake pedal pulsate, then
ABS is reducing brake fluid pressure in
order to insure that wheels continue rotate.
This action may be accompanied by pump
noise.

8. Remember! ABS gives the driver the ability
to steer the vehicle in an emergency braking
situation.
ABS DOs AND DO NOT
DOs
 DO keep your foot on the brake
pedal
 DO allow enough distance to stop.
 DO practice driving with ABS.
 DO consult your vehicle owner’s
manual.
DO NOTS
 DO NOT drive an ABS-equipped
vehicle more aggressively.
 DO NOT pump the brakes.
 DO NOT forget to steer.
 DO NOT be alarmed by clicking
noises.
CONCLUSION
Maximum braking effect is achieved with
the wheels on the limit of friction, whereas
ABS works by releasing the brakes as the
wheels break traction, so a skilled driver
should be able to exceed the braking
performance of an ABS system in a straight
line on a consistent surface. When activated,
the ABS causes the brake pedal to pulse
noticeably. When drivers do encounter an
emergency that causes them to brake hard
and thus encounter this pulsing for the first
time, many are believed to reduce pedal
pressure and thus lengthen braking
distances, contributing to a higher level of
accidents than the superior emergency
stopping capabilities of ABS would
otherwise promise. Nevertheless, ABS can
significantly improve safety and control for
drivers in on-road situations if they know

9. not to release the brakes when they feel the
pulsing of ABS.
PRESENTED BY,
M.NAVEEN KUMAR (11ECL197)
K.MOHAN PREETH (11ECR083)
SECOND YEAR ECE DEPARTMENT,
KONGU ENGINEERING COLLEGE,
PERUNDURAI, ERODE.
MAIL ID:mnaveenkongu@gmail.com
CONTACT NO:7200459528

10. not to release the brakes when they feel the
pulsing of ABS.
PRESENTED BY,
M.NAVEEN KUMAR (11ECL197)
K.MOHAN PREETH (11ECR083)
SECOND YEAR ECE DEPARTMENT,
KONGU ENGINEERING COLLEGE,
PERUNDURAI, ERODE.
MAIL ID:mnaveenkongu@gmail.com
CONTACT NO:7200459528