04-07-2012, 04:08 PM
dynamic speed governor
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INTRODUCTION
The objective of the paper is to present a conceptual model of a microcontroller based variable electronic speed governor that can be implemented to control the speed of any vehicle depending on the local speed limit. The circuit is cost effective, efficient and easy to implement on already existing vehicles. Every city, town or a village, can be marked and divided into individual zones. The division depends upon the area under which the business, residential, and industrial regions come under. The central business district being a very busy traffic zone demands the least speed limit, with the residential and industrial zones having lesser traffic densities, the speed limits will vary accordingly.
Consider a city or town can be divided into physical zones which are classified according to different speed ranges. A transmitter is placed at all exit and entry points of the interface of any two zones that transmits a message signal at carrier frequency, indicating the upper limit value of the zones’ speed range into which the vehicle is entering at that moment, to the receiver which gives the message as an input to a preprogrammed microcontroller embedded within the automobile which compares the speed of the vehicle measured by a sensor at the maximum allowable speed and automatically regulates the speed of the vehicle. The speed of the vehicle can be varied by varying the “duty cycle” of the pulse input. The entire system is a low cost variable electronic speed governor, small in size and easy to assemble onto an existing vehicle without disturbing its present arrangement.
WORKING OF THE SYSTEM
The dynamic speed governor consist of mainly two parts:- the transmitter and receiver. The system is mainly based on micro controller technology for collecting data related to speed and transmits the data to the micro controller using RF communication. The micro controller analyses the transmitted data and takes appropriate decisions related to speed limit and control requirements.
The dynamic speed governor will be needed in populated areas such as hospitals, malls and schools for regulating traffic. The RF transmitter of the system is mounted on the signal board and the micro controller of the transmitter part always sense the speed limit of the area for that the speed limit will be stored in the micro controller. The speed limit of the vehicle will be transmitted using RF transmitter to the approaching vehicles.
An RF receiver is kept inside the vehicle and the receiver accepts the incoming signals and then feeds the limit of speed as an input to a comparator. An RPM meter is used to transform the mechanical rotational movement of the vehicle into an electrical signal and using this method the speed of the approaching vehicle can be detected. This calculated speed from the RPM meter is given to the next input pin of the comparator.
At the comparator both speed given to the both input pin is compared and if the speed of the vehicle is greater than the speed limit the controller will reduce the speed of the vehicle to the limit by using PWM characteristic of the micro controller.
Power Supply
These form an important equipment of any Electronics laboratory. Power supplies are essential for the testing and implementation of any useful electronic circuit. If power supplies are not available then the only way to provide power to a circuit is the battery. For long-term use and frequent manipulation these are not feasible. More over these are not as flexible as modern day power supplies. They do not provide for overload protection and thermal protection.
The following units form the backbone of any modern day power supply
1. Full wave bridge rectifier
2. Filter circuit
3. Voltage regulator
In the case if modern power supplies, the required power is derived from the AC mains. For this at first the 230V/50 Hz is step down using a step down transformer. Then The AC voltage is converted to DC using a rectifier circuit. The bridge rectifier is considered the apt choice since it avoids the center-tapped transformer. The ripples from the rectifier output are removed by filtering.
The filter can be any of the following:
1. L filter
2. C filter
3. LC filter
4. CRC filter
And we use capacitive filtering.
The function of the voltage regulator is to provide a stable DC voltage for powering other electronic circuits. The voltage regulator must be capable of providing substantial output current. They must provide a constant voltage regardless of changes in load current, temperature, and AC line voltage. Although voltage regulators can be designed using op amps, it is quicker and easier to use IC Voltage regulators. Furthermore, IC voltage regulators are versatile and relatively inexpensive and are available with features such as programmable output, current / voltage boosting, internal short –circuit current limiting, thermal shut down, and floating operation for high voltage applications.
Voltage regulator may be classified as:
1. Series regulator
2. Switching regulator
Series regulators use a power transistor connected in series between the unregulated DC input and the load. The output voltage is controlled by the continuous voltage drop-taking place across the series pass transistor. Since the transistor conducts in the active or the linear region, these regulators are also called linear regulators. Linear regulators may have fixed or variable output voltages and could be positive or negative. Voltage regulators such as the 78XX series and the IC 723 are commonly used.
Switching regulators operate the power transistor as a HF on/off switch, so that the power transistor does not conduct current continuously. This gives an improve efficiency over the series regulator. The IC 723 can be used as a switching regulator too.