RPM meter for brushless motor

[coolchip]

motor rpm meter

I am using hall sensor on a brushless motor to measure its rpm using pic.
Need your help/useful links.

Thanks

 

[VVV]

brushless motor rpm

All you need to do is count the number of pulses from the sensor, that you get in a fixed amount of time, say 100msec. Multiplied by 600 that will be the motor's rpm.

One way to do this is to connect the sensor output to a counter input on the PIC. Then, you read the counter at the begining of the timing period and then 100msec later. Subtract the two readings and you get the number of pulses in 100msec.

 

[IanP]

rpm meter which works on pulses

Here you have links to examples of PIC-based rpm meters ..
PIC16F873
http://www.piclist.com/techref/microchip/tacho.htm
PIC18F252
**broken link removed**
PIC16F872
**broken link removed**

 

[coolchip]

how to measure brushless motor rpm

Thanks vvv and IanP.
What signal conditioning/comparator ( r they same?) should I use to get clean logic signal from hall sensor?
It should be compact like a single ic chip.

 

[IanP]

brushless motor care

Some hall sensors have built-in Schmitt-gates, but if you are not sure about your sensor use 4093 Schmitt-NAND gate(s) or 74HC14 inverters between the sensor and the PIC..

IanP

 

[coolchip]

bl motor pic

Are these comparators? Please shed some light on how they work.

Thanks a lot !

 

[IanP]

rpm meter brushless

CD4093 and 74HC14 are not comparators; they are Schmitt treigger NAND gates/inverters.
https://www.fairchildsemi.com/ds/CD/CD4093BC.pdf
https://www.fairchildsemi.com/ds/MM/MM74HC14.pdf
They can shape the incoming signal to a good looking square wave (within certain voltage ranges).

 

[coolchip]

brushless motor rpm measure

All you need to do is count the number of pulses from the sensor, that you get in a fixed amount of time, say 100msec. Multiplied by 600 that will be the motor's rpm.

One way to do this is to connect the sensor output to a counter input on the PIC. Then, you read the counter at the begining of the timing period and then 100msec later. Subtract the two readings and you get the number of pulses in 100msec.

Should I use interrupts to count pulses or is there a better way?
Thanks for help.

 

[Badaruddin]

how brushless motor works pdf

You are right, you need an interrupt, that is time interrupt. This interrupt is generated 100 ms after counting the pulses input.

 

[coolchip]

brushless motor rpm measurement

You are right, you need an interrupt, that is time interrupt. This interrupt is generated 100 ms after counting the pulses input.

Can I use the counter and timer both at the same time for this?
The timer0 acts as counter so how will it measure time simultaneously?
I know the asm language but having problem conceiving the flowchart.
Btw how do you start a project?First make a flowchart or something or simply take a shot at code.

Do I need to take some care for measuring high speed of my brushless motor.It can easily go upto thousands of rpm...~18,000