[sdiy] Hall Effect transistor question

[Ian Fritz]

Hi Michael --

These are *not* transistors.  They are bridge-detector / amplifier 
integrated circuits.  The terminals are ps (+ and gnd) and amplifier 
output.  I used these in the jaw and bender circuits of one of my wind 
controllers:
http://home.earthlink.net/~ijfritz/sos_circ.htm

No, you cannot test it without power.  The Hall effect is a potential 
difference produced by the bending of current trajectories in a magnetic 
field, so you have to supply power to get the current to produce the output 
voltage.  You can look at app notes from Allegro or other companies (they 
change around all the time, so I don't know who is current) for more details.

They *are* fun to play with.

   Ian


At 08:31 PM 4/11/06, Michael Bacich wrote:
>Hello guys,
>
>I'm working on repairing an electric scooter that uses a linear Hall
>effect device as a motor speed controller  It's built into a little
>thumb-operated accelerator control on the handlebar.  Just to
>clarify, the Hall device doesn't connect directly to the motors, but
>is used to open some big pass transistors that are located inside a
>remote motor controller/heat sink box.  The unit runs on a
>rechargeable 36 Volt battery, and the two motors are rated at 150
>Watts each.
>
>I'm trying figure out why the motors are not working, and it looks
>like there may be a problem in the little thumb speed control unit.
>I don't have schematics for any part of the scooter, but I'm going to
>reverse-engineer the thumb controller and draw my own tonight -- it's
>not too complicated.
>
>Unfortunately, without schematics for the thumb controller or any of
>the larger system, I don't really know what kind of signals I should
>expect to be seeing inside the controller.  I don't have any
>experience with Hall effect devices, so can anyone fill me in on
>their basic function, and how they are typically wired?  Are the
>terminals analogous to Collector, Base, and Emitter in a bipolar
>transistor?  This device, BTW, has three leads.  I can't read the
>numbers on the device right now, since it's mounted in an
>inconvenient location -- I'm now working on removing it from the
>housing, hopefully without damaging it or  the cheap plastic housing.
>
>Is it possible for me to do any testing on the Hall device without
>any biasing power connected to it?  That is, will my Ohmmeter show
>any change in reading if I read the device while moving the magnet in
>and out?  (without the power being applied)
>
>BTW, I am only assuming that this is specifically a Hall effect
>device, since it is activated by small magnets that are moved by the
>thumb actuator.  I'm also assuming it's a linear device, and not a
>simple on/off device, since it's possible to smoothly and gradually
>change the motor speed from slow to fast.  Are there any other device
>types that might be used in something like this application that
>perhaps I am not yet aware of?
>
>Also, there are actually two magnets in the thumb wheel:  one that
>rests next to one side of the device when the scooter is at rest, and
>which is pulled away from the device when you accelerate, and another
>which faces the opposite side of the device, and which is moved
>closer to it as you accelerate.  Thus, the two magnets would seem to
>have opposite effects -- possibly one magnet "pushing" the transistor
>open, and the other one "pulling" it closed?
>
>And yes, this indeed Synth DIY -- the scooter is being used as a
>mobile platform for an electronic music performance setup.  It's
>going to be a lot of fun, once we get the motor problem sorted out.
>
>Michael Bacich
>
>