Re: Measuring motor RPM with micro.
- From: John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 14 Jun 2006 15:27:52 -0500
On 14 Jun 2006 05:46:31 -0700, seegoon99@xxxxxxxxx wrote:
Hi all.
I am trying to measure the RPM of a motor and have a few questions.
The motor is turning slowly(about 132RPM after gearing). There is an
"optical encoder"
on the shaft that gives me 8 pulses / rev.This gives me a pulse every
56ms or so.
How can I calculate the RPM of the motor WITHOUT using floating point
routines and in
a fairly fast time.
I could wait 1 second , count the number of pulses / 8 * 60 to get RPM
, but this takes far to long(1s) :0( I can measure fewer pulses , but
the time is still to long.
I could measure the period of 1 pulse , invert / 8 * 60 to give RPM.
This is much quicker , but involves floating point routines. I can gate
a timer in the micro with the pulses from the encoder to give me a
count in the micro , but this will also involve floating point routines
to get back to rpm.
Is there a simple solution to this problem(probably) and I've missed
the boat completely or am I stuck with the options I have described:0(
---
Build a little integrator?
use the one-shot to make all the pulses one width and then use them
to charge a cap:
+----------+
PULSES IN>----| ONE SHOT |--+--[DIODE>]--+-->OUT TO µC ADC
+----------+ | |
+----[R]-----+
|
[C]
|
GND
--
John Fields
Professional Circuit Designer
.
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