Posts Tagged ‘schmitt trigger based control’

Motor control using simple Schmitt trigger.

September 27th, 2011 Remo No comments


Hello here we will see how we can control the speed of a DC motor by using a Schmitt trigger IC.Note the speed of the motor can be controlled by various ways ,may be by reducing the DC voltage across the motor etc .

But here we will follow the most conventional way of reducing/increasing the speed of the motor.The basic principle is if say the motor operates at speed 5 V DC then if this is done by sending a pulse of period say x with x/2 ti,e it has 5V and x/2 time it has 0 V. That means we are sending a square wave with 50% duty cycle.Because 50% of the time period we have HIGH voltage across the Motor(5V) and 50% of the time period we have 0 V across the motor.So what will be the result?

The answer is motor will rotate no doubt.But if we increase duty cycle more ? then ? then the speed of the motor will increase because the motor will now have the DC voltage across it more time,because we increased the duty cycle.How we increased te duty cycle ?simple just now we made a square wave such that 75% of time now there is HGH voltage across the motor and 25% of time there is 0V across the motor.So on the average the motor is getting more voltage in the sense that within one time period of the pulse that is being applied then motor is getting more average voltage when the dutry cycle is HIGH.

Actually what we do is that we configure an astable mutivibrartor such a way that its duty cycle can be varied using a potentiometer. So as the duty cycle can be varied then how this is used with the motor? The answer is the motor is connected with a transistor and the astable output is given at the base of transistor. So the transistor will be made on/off based on the duty cycle that way the Motor will be connected or unconnected with the supply at the same rate as the transistor will be ON/OFF. So this way the speed of the motor can be increased and decreased.

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