Appunti Automotive electronic Systems completi

1.Introduction to electronics

The goal of an electronic system is to acquire information and/or control a physical or chemical process.

Using sensors we can measure quantities that describe the process we are interesting for; sensors translate

the information to the electrical domain, sending information that can be processed from an electronic

system.

A signal conditioning block is used to manipulate the signal sent from sensors before they were translate in

the language of the control unit, the digital one; to perform that transformation, a device called analogic to

digital converter is used.

Information is the ability to distinguish.

The digital information are processed inside a micro-controller that implement hardware and software. If

we want to act back to the physical process, we need to send analog information to control actuator; to do

so we need a digital to analog converter that can translate digital input from the control unit that can be

used in analog language for manipulate the process. Actuator can use a very big amount of power, while

the D/A output is just a analog signal with a small amount of power; an output stage is added so that a little

signal sent from the control unit can control a powerful actuator.

Example: noise cancellation inside the vehicle

Microphones measure the pressure wave due to the noise and convert it into a electrical quantity,

• sending a continues wave signal;

A signal conditioning, in this case an analog filter, is used to manipulate that signal. In our case, the

• filter remove the frequency that microphones catch but they can't be eared from humans;

The signal is ready to be converted as a digital signal that can be processed;

• The digital unit made its own calculation, following an algorithm;

• The result of that calculations are sent to be convert in analog signal. The output of the control unit

• will be a wave with an opposite form of the noise that we want to eliminate;

The output of the D/A is tuned up using an output stage that increase the power of the signal and

• sent it to the actuator, that in this case would be a speaker inside the vehicle.

An electronic system for automotive need to perform in difficult scenarios; it need to work in a large

temperature range, it must be tolerance to humidity, electronic power, speed, contamination, pollution,

dust, vibration, and of course it need to be as light as possible.

Electronic systems can be used for complex engine control systems, like for optimize fuel consumption,

reducing pollution, keep under control the parameters and check for problems. They are used for

navigation, communications, power management, and other in-board task.

Systems are implemented for increase the functionality of an another system; they can be use to automatic

perform task, for increase the safety or for adding information to the driver.

The most complex electronic system inside a car is the ECU, engine control unit; it controls all the engine

parameters using close-loop circuit that can perform instant variation depending of the input signals. The

ECU receives information from several sensors like Lambda, temperature, pressure, air flow and others,

located in different positions on the car and it processes the info received with some algorithm that are

write inside the memory of the circuit. The circuit itself is made out of an embedded circuit on a PCB with

all the connection ports needed for the sensors and the overall is included inside a protection case that also

provide the heat exchange to allow the ECU to stay cool. All modules can then dialogue with a diagnostic

control unit that can register faults and then it can be connected to a service monitor that shows when,

what and why the event happens.

Buses are used to connect different module; they can be used to send the data itself, but also to send

control signals and address signals, which define the direction of the corresponding data.

Every functional block is a circuit made out by different components like resistors, capacitors, inductors,

transistors, switches and others. Many of these blocks also can store information and elaborate them

thanks to a memory module, while other blocks are used to send high power to devices such as actuators

based on a low power input signal.

Circuits can be made in different ways:

Discrete circuits are made up of components produced separately that are then assembled on a

• PCB that integrate all the connections between different components;

Integrated circuits are made up of components that are manufactured simultaneously on the same

• piece of semiconductor; in this way it's possible to build smaller, cheap and more efficient circuits,

but it’s more complex and less versatile.

All the blocks that compose an electronic system need energy; the energy came from the in-board vehicle

battery, which is recharge via a small generator connected to the engine, called alternator. The alternator

produces alternated current that is converted in direct current ready for be stored in the battery.

2.Nuts and bolts of electronics

Electrical components are objects that define an unique relationship between the two main electrical

quantities, voltage and current. Using an analogy, we can consider two tank filled up with some fluid,

connected using a pipe; a different level of fluid generate a different pressure, that make the fluid move.

The same function was made by the voltage in electrical circuit; a voltage different between the two ends

of a component generate a flow of current through it. Voltage is responsible for the electrical current to

Voltage Volt (V),

flow inside components. (electrical potential) is measured in indicate the different of

current

potential between two point (a reference point, like the earth crust, and a point of interest), while

Ampere (A)

is measured in and measure the flow of the electrons; arrows are used to indicate direction of

voltages and currents inside a component. Arrow are placed inside the circuit to indicate the flow of the

current (by convention the direction is opposed to the electrons flow which flow from the negative side to

the positive one), while they are place above the component, between two nodes, to indicate the electrical

potential between them.

The potential indicated is the one that the arrow indicate minus the other. Ampere is equal to Coulomb per

second, which is the unit for electrical charge; this simply because the current is a flow of current, so

ampere indicate how much electrical charge flow in the circuit. Electrical components have at least 2

Watts (W), Coulomb

terminal. Another important dimension is power, measured in capacity, measured in

(C). passive;

Components that can be only absorb energy are called the energy supplied them is dissipated

as heat.

node

A is a point of the circuit in which at least two terminals converge together (red on the image), while a

branch of the circuit is a single path that connect different nodes (blue on the image).

voltmeter,

For measure the potential difference between two nodes we can us a while for measure the

ammeter.

current that flows through a branch we can use an The first one need to be connected in parallel

of the branch defined by the two nodes that we want to measure, while for the ammeter it has to be

positioned in series in the branch, after o before a component. For obtain the measure without influence

the flow of the current, the voltmeter needs to have a high impedance (ideal infinite) to deny the current to

flow in it, while the ammeter needs to have the lowest impedance as possible (ideal zero) so that all the

current pass through it.

BASIC COMPONENTS

Considering the most simple circuit (ideals), there aren't any real components that can work exactly like

these two circuit:

Short circuit: two nodes are connected. Regardless the magnitude and the direction of the current

• flow, voltage between these two will be always zero;

Open circuit: two nodes not connected. Regardless the voltage across these two nodes, the current

• that flows between the nodes is zero.

We can define two types of sources (ideal):

Ideal voltage source: supply to the circuit a constant voltage regardless the magnitude and the

• direction of the current that flows through it. The plus and minus indicate just the type of the end

(negative or positive), doesn't mean that the higher voltage is positioned near the plus and vice

versa.

Ideal current source: supply to the circuit a constant current flow (magnitude and direction)

• regardless the voltage measured across its two ends.

Ideal sources that supply zero volts or amperes are represented, respectively, by short circuit and open

circuit.

For convention, I decide the positive direction of the voltage or the current and then fix that the other

resistor,

quantity are positive in the opposite direction. In a the relationship between current and voltage

(constitutive relation of a resistor, known as Ohm's law) is linear with a factor, called resistance (measured

in Ohm Ω), that indicate the dimension of the resistor.

The ideal relation is perfectly linear, because that value of resistance is constant; also voltage and current

have the same sign, so we can understand that the power that pass through a resistor is positive, this

because resistors are passive components.

= ∗ , = 2

2

= ∗ = ∗ =

Here is showed the different between active devices (like supply sources) and passive (resistors): the power

is dissipated as heat. −1

The reverse of the resistance is conductance, indicated with G and measured in (Siemens):

Ω

−1

= ; = ∗

Kirchhoff's laws are important to resolve an electrical circuit, meaning be able to calculate the voltage in

each nodes and the current that flows in each branch.

Kirchhoff current law: in any node of the circuit the total current that flow in it is zero. Also this

• mean that the total current that flows out a node is equal to the one that entries the node.

� = 0 h

Kirchhoff voltage law: in any loop of the circuit the sum of the voltage must be zero. A loop is

• composed of several branch and is a close path where the starting point and the end are the same

node. � = 0 h

Components can be connected in two different ways:

Series connection: work as a voltage divider, this mean that the current that flows in the

• components is the same, while the voltage can be different. The end of a component is connected

with the input of the other. In case of resistors, the total resistance is given by the sum of the single

resistance values.

= � ; = ; = ∗ → = ∗ � = ∗

The equivalent resistor in a series connection is always greater that the greatest resistor inside it

Parallel connection: work as a current divider, this mean that the voltage of the branches is the

• same, while the current that flows inside the components can be different. All components share

the same node for their entries, and another node for their exits. In case of resistors, the total

impedance is given by the sum of the single impedance values. 1 1

1 2

= � ; = ; = ∗ → = ∗ � = ∗ ; = � → = =

1 1 1 +

1 2

+

1 2

The equivalent resistor in a parallel circuit is always lower than the lowest resistor inside it.

Example: consider this circuit

R6 and R7 are a series connection, their equivalent resistor are in a parallel connection with R5; this

equivalent are in series with R4, as R2 is with R3. these two equivalent resistor are in parallel, and their

equivalent is in series with R1. The result is a single equivalent resistor that replicate the resistance of the

previous circuit:

Capacitor is a passive device that can be used to storage electric charge; it's characterize by its capacity C,

measured in Farad [F]. The constitutional law of a capacitor is:

= ∗

Since the current is the amount of electric charge that flow per second, it can also be written:

= → = ∗

The capacitor establish a linear relation between the derivate over time of the voltage and the current that

flows in it. Applying a constant current at its ends, the voltage rise linearly with a speed equal with a rate

equal to I/C.

If the current is not constant, the voltage will vary in consequence; when the current is positive, the voltage

will rise, when the current is zero, the voltage will be stable, while when the current is negative, the voltage

will decrease.

Inductor is a passive device (dual of capacitor), it's establish a relation between the voltage and the

derivate over time of current that flows through it:

= ∗

It's characterize by an inductance, measured in Henry [H]. The inductor store energy in the form of

magnetic energy; we can vary the energy stored by varying the voltage at its ends.

Capacitor and inductor respond to a variation in the circuit of, respectively, voltage and current.

Capacitor can be charged with electric charge by letting current flows in it (for the inductor is the dual).

Consider the circuit below, a voltage supply is connected with a switch to a resistor and a capacitor in a

series connection; there is one branch and one loop, this mean that the current flows through the

components is the same.

When the switch is open its work like an open circuit, while when it's close its work as a short circuit.

∫

= + + = + + = + +

h : = + ; h : = +

At the start the capacitor is empty, its voltage is zero and the current that flow in the circuit is based on the

Ohm's law:

= 0 → = 0, = 0, =

As the time pass, the capacitor will charge at a point that its voltage will be the same as the one of the

source; this mean that the current that flows will be zero.

= ∞ → = , = , = 0

This mean that as the charge of the capacitor rise, its voltage will rise but the current that flows through the

circuit will decrease at zero when the charge is completed. The charge of the capacitor follow the solution

of the differential equation:

− −

− =

= + → =

�1 �

RC is the time when we reach the 63% of the complete charge, after a time of 5RC the charging process can

be assumed done; RC is also indicate with τ, which depends on the resistor and capacitor used. The role of

the resistance is not related on the charge that capacitor can storage, but just at the time that the fully

charge will be performed, and so the initial current of charging; small resistor permit a higher current and a

lower time of charge. superposition

When more than one independent source is present in a linear circuit, we can apply the

principle in this way: draw n equivalent circuits by keeping only one source per equivalent circuit and then

superpose the effect. The eliminated source have been replaced with short circuit.

Thevenin and Norton theorems can be used to create equivalent circuits from a difficult network.

Thevenin theorem: a generic black-box non-dynamic linear circuit observed by two nodes can be

• always represented by a voltage source in series with a resistor

Norton theorem: a generic black-box non-dynamic linear circuit observed by two nodes can be

• always represented by a current source in parallel with a resistor

The equivalent circuit from Thevenin and Norton have the same characteristics.

Signals are a function over time. Electrical signals are classified in two types:

direct current.

DC means Its voltage and current signals are constant over time

• alternating current.

AC means Its voltage and current signals varying over time; thanks to the

• Fourier theorem, every AC signal can be seen as the superposition of sine waves with different

frequencies and amplitudes. The number of these sine waves depend on the particular signals to be

represented, they can be infinite.

A signal can be represent with its spectrum; it uses the frequencies domain, and gives the information also

of the amplitude of the single sine waves that form the signal.

A sine wave is define by its amplitude, its frequency, and its initial phase; it's a periodic function. If a signal

is periodic in the time domain, the first sine wave that is used for represent the signal will have the same

frequency, the second wave will have double the frequency and so on, every sine wave have a frequency

double of the previous wave.

A zero frequency cosine wave is a constant signal; the average sum of a signal components that