how to display rpm using proximity sensor?

[Naveen Naveencs]

I want to count the proximity sensor output and convert it into rpm.can any one explain

 

[betwixt]

1. find out how many pulses your proximity sensor produces per revolution. (pulses per revolution)
2. count the number of pulses in one minute. (pulses per minute)
3. RPM = (Pulses per minute) / (pulses per revolution)

Brian.

 

[Naveen Naveencs]

Thank you u for ur post i will try it and say the result...

 

[Naveen Naveencs]

1. find out how many pulses your proximity sensor produces per revolution. (pulses per revolution)
2. count the number of pulses in one minute. (pulses per minute)
3. RPM = (Pulses per minute) / (pulses per revolution)

Brian.

1.i am using 16f877a for controlling speed of a dc motor in both direction (5-500 rpm).
2.i am getting 1 pulse in proximity sensor per revolution.
3.so for counting the pulse i created 250ms in timer interrupt .that timer counts the external interrupt and save in a variable.
then i convert the count for 1 min .
Example:
for 250ms the count is 1;
then for 1sec it will be (count =count*4).then for 1min (count=count*60)
please tell my calculation is correct or not

 

[betwixt]

That is correct. Be careful with the formulas though because it is possible at low speeds that you will get no interrupts at all within 250mS so you could get strange results.
There is a 'trade off' between accuracy and how fast you need to see the results. Obviously to get the most accurate RPM you have to count over the whole minute. If you measure over shorter periods the answer will update more frequently but you lose accuracy, for example, if you use (count = count * 4) the result can only be in steps of 4. Personally, I would set the timer period so you are sure to capture at least one pulse at the slowest RPM, for example 5 RPM = 1 pulse every 12 seconds so use at least a 12 second interrupt period to count in.

Brian.

 

[Naveen Naveencs]

Thank u for ur idea.I also thinking about the same .i will forward my result to u

 

[Naveen Naveencs]

i nearly getting nice speed control and display,by calculting the time period between two external interrupts.