UML (Unified Modeling Language) high-level schematic of a remote controller toy car system.

Abstract:  Control functionality of modern vehicles is getting more and more complex. Programming complex embedded systems involves reasoning through intricate system interactions along paths between sensors, actuators and control processors. This is a time-consuming and error-prone process. Furthermore, the resulting code generally lacks modularity and robustness. Model-based programming addresses these limitations, allowing engineers to program by specifying high-level control strategies and by assembling common-sense models of the system hardware and software.

Introduction:

Today’s software development has big challenges to master like shortened development times for the cars in total versus longer development times for the software, high safety requirements and especially the growing complexity because of the rising number of functions and the increasing interaction between the functions. To master these challenges car producers and suppliers conduct a paradigm change in the software development from hand-coded to model-based development. 2 A model-based development process is specifically attractive in embedded domains like Automotive Software due to the fact that development in these domains is driven by two strong forces:

• On the one side the evolutionary development of automotive systems, dealing with the iterated integration of new functions into a substantial amount of existing functionality from pervious system versions;
• On the other side platform-independent development, substantially reducing the amount of reengineering/ maintenance caused by fast changing hardware generations. As a result, a model-based approach is pursued to enable a shift of focus of the development process on the early phases, supporting a function based rather than a code-based engineering of automotive systems.

Earlier, many embedded applications were developed using assembly level programming. However, they did not provide portability. This disadvantage was overcome by the advent of various high-level languages like C, Pascal, and COBOL. However, it was the C language that got extensive acceptance for embedded systems, and it continues to do so. The C code written is more reliable, scalable, and portable; and in fact, much easier to understand. Embedded C Programming is the soul of the processor functioning inside each and every embedded system we come across in our daily life, such as mobile phones, washing machines, and digital cameras. Each processor is associated with embedded software. The first and foremost thing is the embedded software that decides to function of the embedded system. Embedded C language is most frequently used to program the microcontroller

What is C Language?

C language was developed by Dennis Ritchie in 1969. It is a collection of one or more functions, and every function is a collection of statements performing a specific task.
C language is a middle-level language as it supports high-level applications and low-level applications. Before going into the details of embedded C programming, we should know about RAM memory organization.

The main features of the C language include the following.

• C language is software designed with different keywords, data types, variables, constants, etc.
• Embedded C is a generic term given to a programming language written in C, which is associated with a particular hardware architecture.
• Embedded C is an extension to the C language with some additional header files. These header files may change from controller to controller.

What is an Embedded C Programming ?

In every embedded system based projects, Embedded C programming plays a key role to make the microcontroller run & perform the preferred actions. At present, we normally utilize several electronic devices like mobile phones, washing machines, security systems, refrigerators, digital cameras, etc. The controlling of these embedded devices can be done with the help of an embedded C program. For example in a digital camera, if we press a camera button to capture a photo then the microcontroller will execute the required function to click the image as well as to store it. Embedded C programming builds with a set of functions where every function is a set of statements that are utilized to execute some particular tasks. Both the embedded C and C languages are the same and implemented through some fundamental elements like a variable, character set, keywords, data types, declaration of variables, expressions, statements. All these elements play a key role while writing an embedded C program.

The embedded system designers must know about the hardware architecture to write programs. These programs play a prominent role in monitoring and controlling external devices. They also directly operate and use the internal architecture of the microcontroller, such as interrupt handling, timers, serial communication, and other available features.

1.  Differentiate between the embedded C programming and model based system approaches. 

2. a.) Draw a high-level schematic of a remote controller toy car system. Explain the working principle of the toy car system?

                                                                   The first remote controllers were developed in the early 1990s, and the first remotes were connected with wires to devices. Nowadays remotes use infrared control and thus are capable of controlling several things at a time. The remotes are not only used for entertainment, but also for industries, military requirements, and recreation. Infrared remote controls were developed in the late 1970s. These remote controls are based on the principle of using infrared light as the medium of communication. And use photo receptors and different light frequencies for different functions. These remotes also use invisible light beams to send signals to electronic devices. Radio-controlled or remote-controlled toys, popularly called RC toys, are self-powered and can be controlled from a distance using a remote that works with radio waves.

1. When we push the control, the transmitter sends a specific number of electrical pulses corresponding to that action through the air. The transmitter has its own power source, usually in the form of a 9-volt battery. Without the battery, the transmitter will not be able to send the radiowaves to the receiver.
2. Once the RC toy receives the radio waves, the motors kick into life to cause a specific action to occur. The power source sends power to all working parts, including the motor. The transmitter enables control through radio waves and the receiver activates the motors. When we press a button on the transmitter to make the RC toy go forward or backward, a pair of electrical contacts touch. Receiver identifies signals, sends it to circuit.
    Circuit board translates the number of electrical pulses (signals) into action. Full-function controllers have six controls and these works through following the pulse sequences:
3. 1. Forward: 16 pulses
   2. Reverse: 40 pulses
   3. Forward left: 28 pulses
   4. Forward right: 34 pulses
   5. Reverse left: 52 pulses
   6. Reverse right: 46 pulses

BLOCK DIAGRAM:

To build a RC car we need to make sure that these blocks are available. The above blocks are divided into two sections Remote and Car for the purpose of understanding. Starting from Keypad which controls the movement of the Car whereas Encoder and decoders are meant to encode and decode the movement signals for secured transmission. Also transmitter sends the movement signals through wireless medium and receiver fetches the signals for the destination.

CIRCUIT DIAGRAM OF REMOTE CONTROL: (Transmitter)

The above Remote control Circuit consists of three important components Keypad, Encoder IC HT12E and a RF Transmitter RF433 module.

KEYPAD: The Keypad for our remote is made up of four individual buttons which is wired to the data pins of the data pins AD0 to AD3 of the encoder IC. When these buttons are pressed it passes the movement signals to the encoder,

ENCODER HT12E: This encoder serves the purpose of encoding the movement signals fed by the individual buttons. The Data pins AD0 to AD3 is active low hence pressing the button closes the circuit and a logic 1 or high signal is fed to these pins. It also contains Address Pins A0 to A7 which allow us to try out different address combinations for secured transmission of data but make sure you use the same address combination in the receiving end (decoder). In the above circuit we did’t try out any address combinations hence all the pins are grounded. The Dout Pin gives the encoded output data.

RF433 TX: This is a simple RF433 TX module which operates at frequency at 433MHz. The encoded data from the Encoder is fed into DIN pin of the TX and a simple antenna is attached to its 4th pin.

OSCILLATOR FREQUENCY: The Oscillator frequency of HT12E is 3.25Khz (refer the oscillation frequency vs supply voltage graph in the datasheet). This frequency is fixed using the resistor R1 ( 1.1M ) . Modifying this resistor value will alter the output frequency.

CIRCUIT DIAGRAM OF REMOTE CONTROL: (Receiver side)

RF433 RX: This simple RF433 RX module which operates at 433MHz. The received encoded data signals are received through the antenna and the signal is obtained from DATA pin to feed the decoder.

HT12D DECODER: The encoded signals from the RX module is fed into the DIN pin of the decoder. The signal is then decoded by the decoder; remember to use the same address combination used in the encoder if any otherwise the movement signals will be interpreted incorrectly. The decoder also consists of VT pin which serves as a identification if any RF link is established, LED was connected to this pin for identification.

OSCILLATION FREQUENCY: For successful reception of incoming signal and decode them, the HT12D oscillation frequency should be 50 times the encoder oscillation frequency. In our case HT12E oscillation frequency is 3.25 KHz, hence our decoder oscillation frequency should be 162.5 KHz. Fixing the value of R1 as 62K does this job (refer the oscillation frequency vs supply voltage graph in the datasheet).

L293D: This IC serves as a Bidirectional motor driver. It is highly impossible to drive heavy loads such as motors using decoder IC hence we have used a dedicated L293D IC for this purpose.

MOTORS: Two simple DC motors are used for the movement of RC Car. A motor for moving the Car forward and backwards whereas the other one is used to steer the car left and right.

  b.) What are the differences between a remote control toy car and an actual electric vehicle?

 2. c. State its limitations

Limitation of EV:

• Electric cars have a shorter range than gas-powered cars.
• Recharging the battery takes time.
• They are usually more expensive than gas-powered cars.
• It can sometimes be difficult to find a charging station.
• There aren't as many model options.
• Over heating ECU's can cause fire.

 Limitation of RC Toy CAR:

 The batteries are often at the root of many RC problems. Not running at all, running very slowly, or even stopping suddenly can be battery-related.

• Missing batteries. Check the RC and transmitter.
• Installed wrong. Make sure the batteries are in the right slots, facing the right direction, and completely seated in their little slots.
• Old batteries. Try some fresh batteries. Or if you're using a cheap brand of batteries, try a different brand. If using a battery pack, make sure it is fully and properly charged.
• Corrosion. If the vehicle has been sitting for a long time or the battery compartment has been exposed to moisture and air there could be some corrosion. In addition to replacing the batteries, clean the battery contacts.