Latching Hall effect sensor

way back in the 1950s they used to pulse toroid magnets that did something like this for switching , pulsing 2 in opposite direction I guess you could make it a latching circuit. But I dont think they do it that way any more. Never heard of  a latching hall effect sensor.  Let us know if you find anything.

Dale H

Include "bipolar" in your search at Mouser (or DigiKey) - dozens of hits including OC output and TO-92-like packaging.  Perhaps obvious but the latching is electronic (continuous power required) as opposed to a typical mechanical latching relay.

I did use bipolar latching and did come up with hits.  However looking at data sheets, it seems that the output latches on while magnet near then releases after magnet moves away (built in hysteresis).  So this gives a steady bounce free output to what ever it drives.

So what I am looking at would be a device that latches on with one polarity and releases with opposite, and remains in that state until acted upon by other polarity.

I don't see any that actually latch, that's a logic function that would likely be added external to the sensor.

Hmm.  So I searched DK for "bipolar hall sensor".  The first device in a TO-92-like package was this one and less than a buck. 

It trips when you apply +100 Gauss, it releases when you apply -100 Gauss.  From the data sheet:

When the magnetic flux density (B) is larger than operate

point (Bop), output is switched on (DO pin is pulled low). The

output state is held on until a magnetic flux density reversal

falls below Brp. When B is less than Brp, the output is

switched off.

Perhaps I don't understand what you guys mean by latching?

Actually, I think you do understand, not sure how I missed that one.

Allegro makes a device but it is in a surface mount package, but it does latch and remains on with one polarity and unlatches and remains off with other polarity.

Will do more looking tonight.

Why was part of my answer pulled inside the light gray box? I typed my replay out side it and then removed the unwanted lines from inside light gray box.  Oh well can't have everything.

Would latching reed switches be of any help? I use them to run battery circuits, lights, etc. in model trains, boats. Pass a magnet over it to stay on, pass it again, drops out. Very low current carrying so a relay might be needed or something else would work. I get my reed switches from a guy around Pittsburgh.

Frank

The hysteresis of this device straddles the zero axis, which means the device will latch AS LONG AS POWER IS APPLIED.  If power is removed, the device will drop out.

Nice to know about this option!!

These are NOT rare devices!  Both Mouser and DK have several parts in TO-92-like pkg with OC output and under $1.  Perhaps we can focus on the ATS177 device above and sort out why this doesn’t work for you?

So you approach the device with a “+” polarity magnet.  When you reach +100 Gauss at the sensor, it turns on.  It stays on even as you back the magnet away.  It stays on with no magnet present (or, as Dale M astutely points out, the hysteresis straddles zero).  It only turns off if you apply –100 Gauss.  It stays off even as you back the magnet away. It stays off with no magnet present.  Replace “+ / –“ with “North / South” pole of a magnet if that makes more sense. 

Or if you can share your application, we can talk in those terms.  For example, a few years back there was a guy who wanted to turn on passenger car lights as they left the yard. A fixed track-side magnet tripped a latching circuit in each car so the lights came on car by car as they leave the yard. The lights stayed on during mainline operation (that is, no magnet present).  When the cars returned to the yard, the lights turned off car by car as they passed a different track-side magnet. IIRC maybe a buck in parts per car.

I love this forum.  Regardless of how many years of experience you have or what union you belong to, you always learn something here.

Stan, Great idea on the conventional control of lighting.

I assume you could trigger it on the uncoupling track too.  G

So you don't have to alternate magnet polarity?  That's pretty neat.  I've only seen the type that set on one polarity and reset on the reverse polarity.  How much are they and do you have a data sheet?

Whats old is new again.  There was an article in an old, old Model Railroader magazine where it discussed latching Hall effect sensors. A neat application was to have two senors set up with one before and after a RR crossing, wired in parallel.  A loco with a magnet would trip the first sensor turn on the flashers.  It would also trip the sensor after the flashers.   The caboose had an opposite polarity magnet that would turn off the first but the second kept everything going.  When the caboose went over the second sensor, the flashers went off.

So I wanted to do the same to avoid the hassel of sawing track sections into insulated track and wiring.  Thus I started looking at Mouser and Digikey Hall effect sensors but the data sheets aren't real clear anf seems these sensors are geard toward speed sensors and brushless fan motors and not the N/S latch/unlatch function.  Plus I have probably forgotten my engineering Intro to Magnetism 101 course stuff by now.

Stan,

The latching reed costs around $.75 plus shipping I got a dozen at one time a while ago. I need to order more so I have to find the address and no I don't have any specks on them,yet. I'll try to report back. Here yo go, for $1 each

dave@davebodnar.com ) also, try Mouser, Digi- Key or Damer electronics. Just do a Google search for latching reed switch. Dave even has a page showing how to put it in the circuit.

Frank

Actually, the Diodes, Inc. ATS177 seems to be just what you'd be looking for in this application.

Yes,  Using two diodes, one from the uncoupler and the other reversed with unloader bottom could give you positive and negative half cycle respectively.  G

When you figure out how to do that with the multileaf pushbuttons, please post it here.  I don't think it is as easy as it sounds.

It would be easy to have it half rectified for one direction, but I agree you would need another with the coil leads swapped to get the other magnetic polarity.  If you were not worried about the operating blades, you could move the insulating stubber down one leaf, and wire the both leads of the coil back to the controller such that one button would energize the coil in one direction, and the other button the opposite, while powering the controller from a separate source.  G

Sam,

A Sprague UGN3035U is a Hall Effect Latch that exhibits what I believe to be the operation you want. You can do a Google search for that part number and download the Datasheet. I have used it and it works fine.

I still have a Sprague Hall Effect demo board that is over 25 years old and has three Hall Effect sensors: A linear function that senses polarity and is wired to turn the LED green or red according to polarity; a plain switch that switches on/off in the presence/absence of a magnet; and the latch, which alternates the two LED's according to the magnetic pole in proximity. The corresponing LED will turn on and remain on until the other magnetic pole turns it off and turns the other LED on.

I could not find the latch used on this board, the N275809, either online or in my 1984 Sprague Integrated Circuit Handbook.

I hope this is of some help.

Alex

I just got a schematic of a motor control device at the office this afternoon that uses a

Board Mount Hall Effect/Magnetic Sensors 20mA Latch 5V/9V/12V/15V/18V/24V 3Pin Mouser 785-SS466A

Haven't had time to look up the specs yet, but it's used with a magnet on a shaft as a tachometer for a motor that runs several thousand rpm.

Lad

That board is exactly one my engineering boss showed me several years ago demonstrating these sensors.  Then he lost the board so I could not find the device part number as a starting point for my experimenting now.  However thanks to forum members I will be ordering several Honeywell different types to see what does/not work.

One game changer since that board was made (presumably before Allegro took over Sprague’s sensor products decades ago) are low-cost Nd magnets. These ought to make your job much easier. 

For example, I measure about 100G at 1 cm from surface of this 38 cent 6 mm diameter x 3 mm thick ( 1/4” x 1/8" ) Nd disc.  

Out of curiousity what type/size magnet and distance-to-sensor does your magazine article show?

Thanks for tracking that down and the link.  I see he also sells them on eBay.  To his credit he is quite forthcoming about where he gets them which probably explains the lack of specs.  

Now that we know the application, the latches are track-side with continuous un-interrrupted power which somewhat demotes the value of the mechanical memory of a latching reed... in my opinion that is.

Wonderful! now I have a source for magnets!  I was thinking of Edmund Scientific for these.

Stan, the Model Railroader magazine did not state the distance, and it was applicable to HO trains where the sensor was middle of track and small magnets glued to bottom of loco and caboose.  However, I don't see why it could not be applied here, though the steel track may affect the magnet intensity or shield the senor so I may order two types with higher and lower gauss sensitivity.  They are relatively cheap, so if it doesn't work no harm, no foul (wouldn't be the first time a "brilliant" project derailed).