ECU Components

The processor is packaged in a module with hundreds of other
components on a multi-layer circuit board. Some of the other
components in the ECU that support the processor are:

* Analog-to-digital converters - These devices read the
outputs of some of the sensors in the car, such as the oxygen
sensor. The output of an oxygen sensor is an analog voltage,
usually between 0 and 1.1 volts (V). The processor only
understands digital numbers, so the analog-to-digital
converter changes this voltage into a 10-bit digital number.

* High-level digital outputs - On many modern cars, the
ECU fires the spark plugs, opens and closes the fuel
injectors and turns the cooling fan on and off. All of these
tasks require digital outputs. A digital output is either on
or off -- there is no in-between. For instance, an output for
controlling the cooling fan might provide 12 V and 0.5 amps
to the fan relay when it is on, and 0 V when it is off. The
digital output itself is like a relay. The tiny amount of
power that the processor can output energizes the transistor
in the digital output, allowing it to supply a much larger
amount of power to the cooling fan relay, which in turn
provides a still larger amount of power to the cooling fan.

* Digital-to-analog converters - Sometimes the ECU has to
provide an analog voltage output to drive some engine
components. Since the processor on the ECU is a digital
device, it needs a component that can convert the digital
number into an analog voltage.

* Signal conditioners - Sometimes the inputs or outputs
need to be adjusted before they are read. For instance, the
analog-to-digital converter that reads the voltage from the
oxygen sensor might be set up to read a 0- to 5-V signal, but
the oxygen sensor outputs a 0- to 1.1-V signal. A signal
conditioner is a circuit that adjusts the level of the
signals coming in or out. For instance, if we applied
a signal conditioner that multiplied the voltage coming from
the oxygen sensor by 4, we'd get a 0- to 4.4-V signal, which
would allow the analog-to-digital converter to read the
voltage more accurately.

* Communication chips - These chips implement the various
communications standards that are used on cars. There are
several standards used, but the one that is starting to
dominate in-car communications is called CAN (controller-area
networking). This communication standard allows for
communication speeds of up to 500 kilobits per second (Kbps).
That's a lot faster than older standards. This speed is
becoming necessary because some modules communicate data onto
the bus hundreds of times per second. The CAN bus
communicates using two wires.

Advanced Diagnostics

Another benefit of having a communications bus is that each
module can communicate faults to a central module, which
stores the faults and can communicate them to an off-board
diagnostic tool.

This can make it easier for technicians to diagnose problems
with the car, especially intermittent problems, which are
notorious for disappearing as soon as you bring the car in
for repairs.

Car Computers

Each year, cars seem to get more and more complicated. Cars
today might have as many as 50 microprocessors on them.
Although these microprocessors make it more difficult for you
to work on your own car, some of them actually make your car
easier to service.

Some of the reasons for this increase in the number of
microprocessors are:

* The need for sophisticated engine controls to meet
emissions and fuel-economy standards
* Advanced diagnostics
* Simplification of the manufacture and design of cars
* Reduction of the amount of wiring in cars
* New safety features
* New comfort and convenience features

In this article, we'll take a look at how each of these
factors has influenced the design of your car.

Sophisticated Engine Controls

Before emissions laws were enacted, it was possible to build a
car engine without microprocessors. With the enactment of
increasingly stricter emissions laws, sophistic­ated control
schemes were needed to regulate the air/fuel mixture so that
the catalytic converter could remove a lot of the pollution
from the exhaust.

Controlling the engine is the most processor-intensive job on
your car, and the engine control unit (ECU) is the most
powerful computer on most cars. The ECU uses closed-loop
control, a control scheme that monitors outputs of a system
to control the inputs to a system, managing the emissions and
fuel economy of the engine (as well as a host of other
parameters). Gathering data from dozens of different sensors,
the ECU knows everything from the coolant temperature to the
amount of oxygen in the exhaust. With this data, it performs
millions of calculations each second, including looking up
values in tables, calculating the results of long equations
to decide on the best spark timing and determining how long
the fuel injector is open. The ECU does all of this to ensure
the lowest emissions and best mileage. See How Fuel Injection
Systems Work for a lot more detail on what the ECU does.

A modern ECU might contain a 32-bit, 40-MHz processor. This
may not sound fast compared to the 500- to 1,000-MHz
processor you probably have in your PC, but remember that the
processor in your car is running much more efficient code
than the one in your PC. The code in an average ECU takes up
less than 1 megabyte (MB) of memory. By comparison, you
probably have at least 2 gigabytes (GB) of programs on your
computer -- that's 2,000 times the amount in an ECU.

The Future of Space Exploration

NASA wants the Orion CEV to be versatile for future space
exploration. They project that it will be able to transport
crews to the International Space Station by 2014, the moon by
2020. Mars will be the next goal.

The main objective of the CEV is a return to the moon. During
the design stage of the Apollo, there were two proposals to
put man on the moon:

* The Earth Orbit Rendezvous (EOR) - pieces of a large
moon rocket would be assembled in Earth orbit and launched to
the moon
* The Lunar Orbit Rendezvous (LOR) - two smaller
spacecraft (command/service module and lunar module) would
meet in lunar orbit

Scientists eventually agreed that the LOR approach would save
more weight and achieve President John F. Kennedy's goal of
landing a man on the moon within 10 years. The flight plan
for the CEV return to the moon incorporates elements of both
the EOR and the LOR.

The CEV lunar missions will establish a lunar base to explore
the moon and search for water at the moon's South Pole
(necessary for surviving on the moon and a potential source
of material to make rocket fuel). They will also allow
astronauts to test equipment and techniques for future
missions to Mars. Since the moon is only three days away, it
is safer and less expensive to launch missions to Mars from
there. A rescue mission would also be easier for a lunar
mission than a Mars mission. The CEV will serve as a model
for designing other deep space, manned spacecraft.

With the CEV, NASA hopes to return astronauts to the moon and
make real the dream of sending humans to explore Mars and the
rest of the solar system.