Microcontroller Based Speedometer Cum Distancemeter

Normally, digital speedometers are found only in luxury cars and high-end motorbikes.Even if your motorbike has a mechani- cal speedometer, what will you do when it gets damaged? First, you need to replace the mechanical worm gear and then the cable.

Anyway, we describe here how to build a digital speedometer-cum- odometer for your motorbike. The circuit uses a microcontroller, an LCD display and some commonly available components. It is a better alternative to the mechanical speedometer and even a beginner with minimal skill level can assemble it.

The features of the digital speedo-meter-cum-odometer are:

1. Digital readout

2. Speed displayed in km/hour

3. Distance traveled displayed in kilometres

4. Readings saved in non-volatile memory (EEPROM)

5. Reliability due to use of the mi-crocontroller

6. No mechanical wear and tear

7. Home-brewed speed transducer/sensor

8. Self reset to zero after completion of 99,999.9 km

9. Easy to build and fix onto the bike

Calculations:

You first need to know the radius of the bike’s front wheel. The calculations here are based on Hero Honda’s Splen- dor model. The radius of the front wheel is 30 cm. (This can vary with the brand or model.)

Circumference of the wheel= 2pr (where ‘r’ is in cm)

= 2×3.14×30

= 188.4 cm or 1.884 metres

Speed. Let’s assume that in 1 second the wheel completes one revolution. In other words, in one second, the bike has covered 1.88 metres.

Therefore the speed in km/hour:

N×1.88×3600/1000

= N×6.784 or N×6.8

where ‘N’ is the number of revolutions per second. ‘6.8’ is a constant and only

‘N’ varies; for example, if ‘N’ is 5, the speed equals 5x6.8= 34 km/hour.

Distance. The odometer is updated every 100 metres. To cover 100 metres, the wheel is required to make ap- proximately

53 revolutions (100/1.88). The microcontroller takes care of the tasks of revolutions counting, speed calculation, conversion and display of results.

Circuit description:

The circuit of the microcontroller-based digital speedometer-cum-odometer is shown in Fig. 1. The functions of vari- ous components used in the circuit are described below.Microcontroller A 40-pin AT89C2051 microcontroller from At- mel is used here because of its low pin count, affordability and compatibility with CISC-based 8051 famil available pins of the microcontrol- ler are utilised in the project.

This m i c r o c o n t r o l l e r features 2 kB of Flash, 128 bytes of RAM, 15 in- put/output (I/O) lines, two 16-bit timers/counters, a five-vector two- l e v e l i n t e r r u p t a r c h i t e c t u r e , a full-duplex serial port, a precision analogue compa- rator, on-chip os- cillator and clock circuitry.

LCD module.

T o d i s p l a y t h e s p e e d a n d d i s - tance traveled, we have used a 16x2 a l p h a n u m e r i c L C D b a s e d o n HD44780 control- ler. The backlight f e a t u r e o f t h e LCD allows data to be visible even at night.

Serial EEPROM.

T h e r e a d - ings of the d i s t a n c e traveled are s a v e d i n an external serial EEP- ROM. Here, a 2 4 C 0 2 serial EEP- ROM based o n P h i l i p s I2C protocol

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