# help me in measuring the speed.

Discussion in 'The Projects Forum' started by onlyvinod56, Oct 15, 2008.

1. ### onlyvinod56 Thread Starter Active Member

Oct 14, 2008
362
1
Hi
I dont want to use any microcontroller. But i want measure the speed of a motor and to display through 7 segment displays. Can anybody give me a simple idea. Sombody suggested me to use phase locked loops. I dont know what it is. Is there any other way to implement this?

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
The easiest way is to put a kind of sensor on the shaft of the motor and sense when it completes one revolution. Also, use a 1KHz square wave oscillator to drive a counter which counts up. The counter will be reset when the sensor indicates a complete revolution. Also, at this instant the value of the counter will be stored in a data register. Then you will multiply this counter value by 1/1000 (the period of the square pulses) to find the time the motor did to rotate one revolution and then divide the circumference of the axis at the point the sensor is sensing a revolution by the time calculated. You can do these multiplications and divisions by using ALU's (arithmetic logic units). Then use appropriate chips to drive your display.

May 16, 2005
5,072
6

4. ### onlyvinod56 Thread Starter Active Member

Oct 14, 2008
362
1
Hi mik3,
My intention is not to use microcontroller.
you are using the terms like ALU and registers.
My actual theme is maintaining a constant speed for induction motor at a required speed.
My reference speed should be always compared with the speed of the machine and so that i can control the firing angle of the triac to maintain the speed constant.
I can implement this by using microcontroller.
But i don't want to use microcontroller.

I have an idea. just see the attachment plz.
A proximity switch is used to sense the speed which produce a pulse / revolution.
If the time gap is converted to voltage, then by using a comparator i can do the further operation.

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5. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
The schematic as drawn will not do what you want. If you wish to use a comparator, you must somehow create a voltage proportional to motor speed. Comparators will only compare voltages, not pules periods.

6. ### onlyvinod56 Thread Starter Active Member

Oct 14, 2008
362
1
Thats what i say.
A comparator will measure the voltages.
I need a circuit that produces a voltage in proportional to time period.
My idea is, A circuit must start producing a ramp voltage at the instant of first pulse and continues upto the next pulse. The magnitude of ramp voltage is our required time proportional voltage.
But i dont have any idea about the circuit that converts time proportional voltage

7. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Another option is to attach a small DC generator on the shaft of the motor and measure the voltage across its terminals which is proportional to speed.