Contact-less Tachometer

Project code:- E39 Project Cost:- INR:- Rs. 3000/- USD:- 75$

The techometer also called revolution counter is an instrument that measure the speed of a rotating machionery. Generally these measurements are rated in round per minute (R.P.M)
Rotating machine could be any prime mover like an electic motor, diesel engine,petro or gas driven engine ,gasturbine,water turbine,steam turbine,and numerous industrial equipments which are driven by any of the above engines

Contact-less Tachometer Block Diagram 

It is desireous to know and control the speed of the engine to a safer limit in order to avoid the damage to the engine.The present article is on how to make a contactless techometer using world’s most powerful micro-controller intel-8051. We have used its derivative atmel-89c2051.As the name, we accurately measure the speed of the rotating shaft without touching the shaft.

In order to know the speed of the machine we need to pick up pulse every round of the engine There are many ways to pickup the pulse from the engine shaft.You can use magnetic sensor and hall effect device.,proximity type of sensors, we can also pickup the pulses from the ignition coil from the petro engines.
In this project I have decided to make our own sensor using a led as light source and a photo transister to picup the pulse. A arrangement has to be made to make a small hole about 5mm near to the outer surface of the wheel .Led or any light source is fixed to the one side of the rotating wheel and photo transister to the other side of the wheel. Light will fall on the photo

transister when the hole on the rotating wheel comes in line with the photo transister and light source or led .This way a pulse is picked up every rovolution .

These pulses are applied to the microcontroller.The general principal involved in this project
Is to count the pulse for two seconds and. And calculate the rpm. Display is refreshed every two seconds.
Two line 16 character lcd has been used here for display purpose.

We have tested the project with a small motor which can be rotated by 1.v to 6volts dc
We found that when we applied 1.5v dc to the motor we checked the pulses on the oscillioscope,we found 25ms pulse.with this it comes to 40 revolutions per second and and these could be multiplied by 60 in-order to calculate rovolution per minute, it worked out to be 2600 R.P.M..And this was very near to the satisfactory value.

Circuit description:
Incoming count pulses from the photo transister are connected to p3.4 pin of the ic2 micro-controller,
Two line by 16 character on each line (2×16) is used in nibble mode .

Circuit is driven by 9v 500m.a. transformer connected to PCON1
Diode D1-D4 forms bridge circuit C1,c2 and c3 are filter capacitors and are part of power supply section..
Ic1 7805 is 5v regulator ic to give stablised supply to microcontroller.

Ld1 is a power indication led. R1 controls the current flowing thrugh led LD1 Crystal X1 along with C5 and C6 gives the necessary clock to microcontroller.

Capacitor C4 and R2 gives the required reset pulse to microcontroller.
Resistor r3 is a pullup resistor to the collector of the photo transister. R4 is a current limiting resistor connected to led. Normal led working voltage is between 2v to 4 v and our power supply is 5v so we need to connect a resistance in series with the led in order to limit the current through led.
Low going pulses are available at the collector of the photo transister and can be checked by the oscillioscope.

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