Re: Sol'n to Speed Feedback?

[Joyce Poon <poonj@ecf.utoronto.ca>]

On Tue, 28 Dec 1999, Tim Vanderhoek wrote: 

> Can you find some more pointers to info about Hall sensors, or explain
> some more of your own knowledge about them? 

It took a long time, but I managed to find the homepage of the Engineering
Design course at Rice University (they build robots in 2nd year too).
Their entire course textbook is online.  I will digest all the information
soon (I printed off a bunch of stuff tonight), and I will go back and read
some more tomorrow.  Hall sensors are indeed mentioned there.  There is A LOT 
of GOOD information at the website in addition to sensors (on electromech
stuff like power system, motor circuits as well as comp stuff like comp
boards and such & programming).  Please have a look at this website: 

	http://www-brazos.rice.edu/elec201/book.html

What exactly do you mean 
> when you say "Hall sensors cost less than $3 each"? 

Well, Hall sensors are listed in my electronics catalog for about $1 to $3
each. 

What exactly does 
> this buy and what type of output would it produce and what type of 
> connection does it need to the motors? 

It is not connected directly to the motors.  I think one attaches an
interrupter blade (like a fan blade) on the shaft.  And every time the
blade passes through the magnetic switch (Hall switch/Hall sensor <I
believe>), the magnetic field changes at the switch.  The Hall sensor
detects the change in magnetic field.  We can keep track of how many times
the signal from the Hall sensor changes within a given period of time and
thus calulate the speed of motor rotation (knowing the circumference for
the rotation).  The output is digital (ie a high equal to the input
voltage (I believe) when there is a change in the field and a low of 0V
when there is no change). 

> [Normally I would look this kind of stuff up myself, but at the moment
>  I'm a little busy reading Malone's jun^H^H^Hwriting and with a couple
>  FreeBSD bugreports I should have dealt with months ago].  

Y2K no doubt... ;) 

Joyce :)