Hall Sensor Identification

[MEB]

Hello, I found this DC motor/gearbox in the trash and decided to play with it. Inside is an encoder device which evidently uses Hall Effect Sensors for motor shaft positioning. This is way out of my league, but I get signals on the scope from one of the sensors with the motor spinning, but none from the other, so I wish to find a replacement sensor. I started reading, but like I said, I don't know enough to spec out a replacement device. So I tried to find a duplicate from the usual methods, but can't. I have enclosed a sketch. The device body is about .090" X .106". It has 4 legs. The drawing is to scale but dramatically enlarged. The leads are flat and preformed as no human bent them to that degree of accuracy. The blue is paint on the front applied I think with a brush (with no precision) and the Identification numbers and letters are on the back and unmistakably visible. Anyway, I would appreciate any ideas. The motor is a Faulhaber but the sticker was unreadable and body not engraved. The motor and gearbox appear to work fine, so the encoder probably caused it to be trash bound. I don't have a need for the motor, with or without the encoder, but I am mental and take it to heart if I can't figure something out! Thanks for the look.

[eccerr0r]

Re: Hall Sensor Identification

Is this from one of those 90mm, etc. fans?
IIRC it has two pins for power/GND and the other two actually are used to control the two motor windings. Not sure if this is the case here though, but something like this is used https://cdn.badcaps-static.com/pdfs/...747e666ef3.pdf

[MEB]

Re: Hall Sensor Identification

Thanks, this is my first endeavor with magnetic sensors so I really know very little and this is going to demand some self education with some help from my friends here. The sensor I am looking for comes attached to a small circuit board about .6" diameter inside a dc motor housing. The shaft has a round disc attached to the shaft which spins with it. There must be one or more magnets in that disk (I don't have a clue) which spin with the shaft triggering these 2 opposing sensors affixed to the board. They are not exactly oriented 180 degrees apart, but fairly close to that. The circuit board has a LM2901DG chip, a handful of 0402 resistors, 3 capacitors and the 2 sensors. I read about using a scope to see square waves and poked around with the motor spinning. I haven't figured out the exact function of the 4 pins have yet, but I can see signals from one sensor and not the other. I checked all the caps and resistors and I ordered another 41 cent chip which I replaced, and get the same results. I am not sure, because I don't have experience with these things, but I am betting on the sensor. But there are many styles, shapes and sizes and I don't have the theory necessary yet to figure out a replacement. But, from your data sheet, I can see that your device is physically too large to fit without motor housing modification, even if it were a suitable replacement. But maybe I can use the pin-out information from your data sheet to narrow down my confusion. Thanks for the reply.

[redwire]

Re: Hall Sensor Identification

With 4 pins it could be a single linear, or dual hall-effect sensor, for speed and direction. Post pics if you want more info.
My guess the "A" is for Allegro, they make hall-effect sensors. The "5" doesn't match any I can see.

[MEB]

Re: Hall Sensor Identification

Thanks redwire. Seems like we are getting closer. I am separated from the device today, but will try to get some pictures tomorrow. I might send my little sketch to Allegro. Maybe it is an old version of something. Thanks for your help.