Body Computer: Summary

Body Computer
A computer is an electronic device that stores and processes data and is capable of operating other devices. The operation of the computer is divided into four basic functions: input, processing, storage, and output. Binary numbers are represented by the numbers 1 and 0. A transistor that operates as a relay is the basis of the digital computer. As the input signal switches from off to on, the transistor output switches from cutoff to saturation. The on and off output signals represent the binary digits 1 and 0. Logic gates are the thousands of field effect transistors that are incorporated into the computer circuitry. The FETs use the incoming voltage patterns to determine the pattern of pulses that leave the gate. The most common logic gates are NOT, AND, OR, NAND, NOR, and XOR gates. There are several types of memory chips used in the body computer; ROM, RAM, and PROM are the most common types. ROM (read only memory) contains a fixed pattern of Is and O's representing permanent stored information used to instruct the computer on what to do in response to input data. RAM (random access memory) will store temporary information that can be read from or written to by the pP. PROM (programmable read only memory) contains specific data that pertains to the exact vehicle in which the computer is installed. EPROM (Erasable PROM) is similar to PROM except its contents can be erased to allow new data to be installed. EEPROM (Electrically Erasable PROM) allows changing the information electrically one bit at a time. NVRAM (Nonvolatile RAM) is a combination of RAM and EEPROM into the same chip. Actuators are devices that perform the actual work commanded by the computer. They can be in the form of a motor, relay, switch, or solenoid. A servomotor produces rotation of less than a full turn. A feedback mechanism is used to position itself to the exact degree of rotation required. A stepper motor contains a permanent magnet armature with two, four, or more field coils. It is used to move the controlled device to whatever location is desired by applying voltage pulses to selected coils of the motor.

Read

Outputs

Duty cycle is the percentage of on time per cycle. Duty cycle can be changed; however total cycle times remains constant
Once the computer's programming instructs that a correction or adjustment must be made in the controlled system, an output signal is sent to an actuator. This involves translating the electronic signals into mechanical motion. An output driver is used within the computer to control the actuators. The circuit driver usually applies the ground circuit of the actuator. The ground can be applied steadily if the actuator must be activated for a selected amount of time. For example, if the BCM inputs indicate that the automatic door locks are to be activated, the actuator is energized steadily until the locks are latched. Then the ground is removed. Other systems require the actuator to be turned either on and off very rapidly or for a set amount of cycles per second. It is duty cycled if it is turned on and off a set amount of cycles per second. Most duty cycled actuators cycle ten times per second. To complete a cycle it must go from off to on to off again. If the cycle rate is ten times per second, one actuator cycle is completed in one tenth of a second. If the actuator is turned on for 30% of each tenth of a second and off for 70%, it is referred to as a 30% duty cycle. FIGURE. Duty cycle is the percentage of on time per cycle. Duty cycle can be changed; however total cycle times remains constant. If the actuator is cycled on and off very rapidly, the pulse width can be varied to provide the programmed results. For example, the computer program will select an illumination level of the digital instrument panel based on the intensity of the ambient light in the vehicle. The illumination level is achieved through pulse width modulation of the lights. If the lights need to be bright, the pulse width is increased, which increases the length of on-time. As the light intensity needs to be reduced, the pulse width is decreased. FIGURE. Pulse width is the duration of on time. (A) Pulse width modulation to achieve dimmer dash lights. (B) Pulse width modulation to achieve brighter dash illumination. Actuators Most computer-controlled actuators are electromechanical devices that convert the output commands from the computer into mechanical action. These actuators are used to open and close switches, control vacuum flow to other components, and operate doors or valves, depending on the requirements of the system. Although they do not fall into the...

Read

Information Processing

The microprocessor addresses the lookup tables in the ROM, retrieves air density information, and issues commands to the output devices
The air charge temperature (ACT) sensor input will be used as an example of how the computer processes information. If the air temperature is low, the air is denser and contains more oxygen per cubic foot. Warmer air is less dense and therefore contains less oxygen per cubic foot. The cold, dense air requires more fuel compared to the warmer air that is less dense. The microprocessor must supply the correct amount of fuel in relation to air temperature and density. An ACT sensor is positioned in the intake manifold where it senses air temperature. This sensor contains a resistive element that has an increased resistance when the sensor is cold. Conversely, the ACT sensor resistance decreases as the sensor temperature increases. When the ACT sensor is cold, it sends a high-analog voltage signal to the computer, and the A/D converter changes this signal to a digital signal. When the microprocessor receives this ACT signal, it addresses the tables in the ROM. The look-up tables list air density for every air temperature. When the ACT sensor voltage signal is very high, the look-up table indicates very dense air. This dense air information is relayed to the microprocessor, and the microprocessor operates the output drivers and injectors to supply the exact amount of fuel the engine requires. FIGURE. The microprocessor addresses the lookup tables in the ROM, retrieves air density information, and issues commands to the output devices. Logic Gates FIGURE. The NOT gate symbol and truth table. The NOT gate inverts the input signal. FIGURE. The AND gate symbol and truth table. The AND gate operates similar to switches in series. FIGURE. The AND gate circuit. FIGURE. OR gate symbol and truth table. The OR gate is similar to parallel switches. FIGURE. Symbols and truth tables for NAND and NOR gates. The small circle represents an inverted output on any logic gate symbol. FIGURE. XOR gate symbol and truth table. A XOR gate is a combination of NAND and NOR gates. Logic gates are the thousands of field effect transistors (FETs) incorporated into the computer circuitry. These circuits are called logic gates because they act as gates to output voltage signals dependingon different combinationsof input signals. The FETs use the incomingvoltage patterns to determine the pattern of pulses leaving the gate. The following are some of the most common logic gates and their operations. The symbols represent functions and not electronic construction: NOT gate: A NOT gate simply reverses binary l's to...

Read

Computer Memory

EPROM memory is erased when the ultra-violet ray contact the microcircuitry
The computer requires a means of storing both permanent and temporary memory. The memories contain many different locations. These locations can be compared to file folders in a filing cabinet, with each location containing one piece of information. An address is assigned to each memory location. This address may be compared to the lettering or numbering arrangement on file folders. Each address is written in a binary code, and these codes are numbered sequentially beginning with 0. While the engine is running, the engine computer receives a large quantity of information from a number of sensors. The computer may not be able to process all this information immediately. In some instances, the computer may receive sensor inputs that the computer requires to make a number of decisions. In these cases, the microprocessor writes information into memory by specifying a memory address and sending information to this address. When stored information is required, the microprocessor specifies the stored information address and requests the information. When stored information is requested from a specific address, the memory sends a copy of this information to the microprocessor. However, the original stored information is still retained in the memory address. The memories store information regarding the ideal air-fuel ratios for various operating conditions. The sensors inform the computer about the engine and vehicle operating conditions. The microprocessor reads the ideal air-fuel ratio information from memory and compares this information with the sensor inputs. After this comparison, the microprocessor makes the necessary decision and operates the injectors to provide the exact air-fuel ratio the engine requires. FIGURE. EPROM memory is erased when the ultra-violet ray contact the microcircuitry. Several types of memory chips may be used in the computer: Read only memory (ROM) contains a fixed pattern of l's and O's that represent permanent stored information. This information is used to instruct the microprocessor on what to do in response to input data. The microprocessor reads the information contained in ROM but it cannot write to it or change it. ROM is permanent memory that is programmed in. This memory is not lost when power to the computer is lost. ROM contains formulas, calibrations, and so on. Random access memory (RAM) is constructed from flip-flop circuits formed into the chip. The RAM will store temporary information that can be read from or written to by the pR RAM stores information that is waiting to be acted upon and it stores...

Read

Microprocessor

Main components of the computer and the Microprocessor
FIGURE. Main components of the computer and the Microprocessor. The microprocessor is the brain of the computer. The microprocessor is constructed of thousands of transistors that are placed on a small chip. The microprocessor brings information into and out of the computer's memory. Hie input information is processed in the microprocessor and checked against the program in memory. The microprocessor also checks memory for any other information regarding programmed parameters. The information obtained by the microprocessor can be altered according to the program instructions. The program may have the microprocessor amicroprocessorly logic decisions to the information. Once all calculations are made, the microprocessor will deliver commands to make the required corrections or adjustments to the operation of the controlled system. The program guides the microprocessor in decision making. For example, the program may inform the microprocessor when sensor information should be retrieved and then tell the microprocessor how to interpret this information. Finally, the program guides the microprocessor regarding the activation of output control devices such as relays and solenoids. Hie various memories contain the programs and other vehicle data that the microprocessor refers to as it performs calculations. As the microprocessor performs calculations and makes decisions, it works with the memories by either reading or writing information to them. The microprocessor has several main components. The registers used include the accumulator, the data counter, the program counter, and the instruction register. The control unit implements the instructions located in the instruction register. The arithmetic logic unit (ALU) performs the arithmetic and logic functions.

Read

Analog and Digital Principles

Analog voltage signals are constantly variable. Digital voltage patterns are either on or off. Digital signals are referred to as a square sine wave
Remembering the basics of electricity, voltage does not flow through a conductor; current flows and voltage is the pressure that "pushes" the current. However, voltage can be used as a signal; for example, difference in voltage levels, frequency of change, or switching from positive to negative values can be used as a signal. The computer is capable of reading only voltage signals. A program is a set of instructions the computer must follow to achieve desired results. The program used by the computer is "burned" into integrated circuit (1С) chips using a series of numbers. These numbers represent various combinations of voltages that the computer can understand. The voltage signals to the computer can be either analog or digital. Many of the inputs from the sensors are analog variables. For example, ambient temperature sensors do not change abruptly. The temperature varies in infinite steps from low to high. The same is true for several other inputs such as engine speed, vehicle speed, fuel flow, and so on. FIGURE. Analog voltage signals are constantly variable. Digital voltage patterns are either on or off. Digital signals are referred to as a square sine wave. FIGURE. Simplified voltage sensing circuit that indicates if the switch is opened or closed. Compared to an analog voltage representation, digital voltage patterns are squareshaped because the transition from one voltage level to another is very abrupt. A digital signal is produced by an on/off or high/low voltage. The simplest generator of a digital signal is a switch. If 5 volts are applied to the circuit, the voltage sensor will read 5 volts (a high-voltage value) when the switch is open. Closing the switch will result in the voltage sensor reading close to 0 volts. This measuring of voltage drops sends a digital signal to the computer. The voltage values are represented by a series of digits, which create a binary code. Binary code is represented by the numbers 1 and 0. Any number and word can be translated into a combination of binary l's and 0's. Binary Numbers A transistor that operates as a relay is the basis of the digital computer. As the input signal switches from off to on, the transistor output switches from cutoff to saturation. The on and off output signals represent the binary digits 1 and 0. The computer converts the digital signal into binary code by translating voltages above a given value to 1 and voltages below a...

Read

Computer Functions

A computer processes the physical conditions that represent information (data). Hie operation of the computer is divided into four basic functions: Input: A voltage signal sent from an input device. This device can be a sensor or a switch activated by the driver or technician. Processing: The computer uses the input information and compares it to programmed instructions. Hie logic circuits process the input signals into output demands. Storage: The program instructions are stored in an electronic memory. Some of the input signals are also stored for later processing. Output: After the computer has processed the sensor input and checked its programmed instructions, it will put out control commands to various output devices. These output devices may be the instrument panel display or a system actuator. The output of one computer can also be used as an input to another computer. Understanding these four functions will help today's technician organize the troubleshooting process. When a system is tested, the technician will be attempting to isolate the problem to one of these functions.

Read

12