ABSTRACT
The aim of our project is to develop prototype of a
product “Digital Speedometer cum odometer”. It can replace ordinary
analog speedometer which has low range and resolution. It's rather inexpensive
and can be used in almost all vehicles. The circuit uses a microcontroller, an
LCD display, speed sensor, Optocoupler and
EPROM for storing the results.
Speed sensor was constructed using a read switch and
magnet. The
read switch closes when the magnet passes across it. When the magnet moves away
from the reed switch, that the reed switch is open .The rotation of the wheel
is sensed by the combined action of a reed switch and magnet fixed on the
wheel. The sensor sends a pulse to the microcontroller each time a revolution
is made. An optocoupler is used to counter the effects of bouncing when the
contact of reed switch is closed. The microcontroller takes care of the tasks of
revolutions counting, speed results.
Two
internal timers of the microcontroller are configured as 8-bit counters to
count the number of pulses generated by the speed sensor. One timer is used to
measure the distance and the other for speed calculation.
The speed
count value is obtained from the counter registers. To speed up the process, a
look-up data table is stored in the ROM that helps the microcontroller to
convert the number of pulses into the corresponding speed values .The ‘distance’
counter is incremented and updated every 100 meters. The timer
overflows and generates an interrupt to notify the microcontroller that 100
meters are covered. The microcontroller saves these readings when the vehicle
is at halt. In other words, when the vehicle is stopped at traffic signals or
before the ignition key is turned off, the last reading is saved to the EEPROM.
The same reading is again retrieved from the EEPROM when the bike is turned on
next time and the readings are updated for each trip. The distance meter
was self
reset to zero after completion of 99,999.9 km. This speedometer cum odometer
was reliability due to use of the microcontroller.
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