1. Embedded Systems (A2425) Design Example: Model Train Controller
T. Ramakrishnaiah
Associate Professor
Department of Electronics and Communication Engineering
VARDHAMAN COLLEGE OF ENGINEERING
Shamshabad, Hyderabad – , India.

2. MODEL TRAIN CONTROLLER
The model train controller, which is shown in the below figure.
The user sends messages to the train with the control box attached to the tracks.
The control box may have familiar controls such as throttle, emergency stop button and so on.
Since train receives its electrical power from the track, the control box can send a signal to the train over the track by modulating the power supply voltage.
T. Ramakrishnaiah
19 March 2020

3. T. Ramakrishnaiah
19 March 2020

4. Requirements Here is a basic set of requirements for the system:
The console shall be able to control up to eight trains on a single track.
The speed of each train shall be controllable by a throttle to at least 63 different levels in each direction (forward and reverse).
There shall be an inertia control that shall allow the user to adjust the responsiveness of the train to commanded changes in speed. Higher inertia means that the train responds more slowly to a change in the throttle, simulating the inertia of a large train. The inertia control will provide at least eight different levels.
There shall be an emergency stop button.
An error detection scheme will be used to transmit messages
T. Ramakrishnaiah
19 March 2020

5. Requirements form Name Model train controller Purpose
Control speed of up to eight model trains
Inputs
Throttle, inertia setting, emergency stop, train number
Outputs
Train control signal
Functions
Set engine speed based upon inertia settings,
Respond to emergency stop
Performance
Can update train speed at least 10 times per second
Manufacturing cost
$50
Power
10W (plugs into walls)
Physical size and weight
Console should be comfortable for two hands, approximate size of standard keyboard. Weight less than 2 pounds
T. Ramakrishnaiah
19 March 2020

6. CONCEPTUAL SPECIFICATION OF MODEL TRAIN CONTROLLER
Objects: Console , Train
Commands: set speed, set inertia, Estop.
Console: panel, formatter, transmitter
Train: receiver, controller, motor interface
A UML sequence diagram for a typical sequence of train control commands
T. Ramakrishnaiah
19 March 2020

7. Class Diagram Subsystem Collaboration Diagram
Shows relationship between console and receiver (ignores role of track):
One console can control up to 8 receivers
T. Ramakrishnaiah
19 March 2020

8. Major Subsystem Roles Console: read state of front panel
format messages
transmit messages
Train:
receive message
interpret message
control the train
T. Ramakrishnaiah
19 March 2020

9. Console System Class Diagram
Panel: Describes analog knobs and interface hardware
Formatter: Turns knob settings into bit streams
Transmitter: Sends data on track
T. Ramakrishnaiah
19 March 2020

10. Train System Class Diagram
Receiver: Digitizes signal from track
Controller: Interprets received commands and makes control decisions
Motor interface: Generates signals required by motor
T. Ramakrishnaiah
19 March 2020

11. Detailed Specification
We can now fill in the details of the conceptual specification:
More classes
Behaviors
Sketching out the spec first helps us understand the basic relationships in the system
T. Ramakrishnaiah
19 March 2020

12. Console Physical Object Classes
T. Ramakrishnaiah
19 March 2020

13. Panel and Motor Interface Classes
panel class defines the controls
new-settings() behavior reads the controls
motor-interface class defines the motor speed held as state
T. Ramakrishnaiah
19 March 2020

14. Transmitter and Receiver Classes
Transmitter class has one behavior for each type of message sent
Receiver function provides methods to:
detect a new message
determine its type
read its parameters (estop has no parameters)
T. Ramakrishnaiah
19 March 2020

15. Formatter Class Formatter class holds state for each train,
setting for current train
The operate() operation performs the
basic formatting task
T. Ramakrishnaiah
19 March 2020

16. Control Input Cases
Use a soft panel to show current panel settings for each train
Changing train number:
must change soft panel settings to reflect current train’s speed, etc.
Controlling throttle/inertia/estop:
read panel, check for changes, perform command
T. Ramakrishnaiah
19 March 2020

17. Control Input Sequence Diagram
T. Ramakrishnaiah
19 March 2020

18. Formatter Operate Behavior
T. Ramakrishnaiah
19 March 2020

19. Panel-active behavior
T. Ramakrishnaiah
19 March 2020

20. Controller Class
T. Ramakrishnaiah
19 March 2020

21. Set-Speed Sequence Diagram
T. Ramakrishnaiah
19 March 2020