question for hunch or burlbark

[Monkeyleg]

I've been trying to find out what brand and model of hall sensor is used in the gimbal windings section of the P2V+. Another member on here said they were Allegro 1326 linear hall effect sensors. However, the sensors are stamped "1425" on the top, and Allegro says that wouldn't be one of theirs.

Do you know what brand or model the sensors are? If not, do you have any idea where to start looking? I sent an email to DJI, but I don't expect to hear anything back.

Thanks for any reply.

 

[timmer]

It looks like the A1425 is discontinued, but there is a replacement for it.

See here and go to the bottom of the page: http://parts.arrow.com/item/detail/allegro-microsystems/a1425lk#RyeE.

 

[Monkeyleg]

The sensors in the P2V gimbal aren't 1425's. 1425's have 4 pins. The P2V sensors have 3. If they were Allegro the number would be preceded by an A.

I've looked at a ton of sites but haven't been able to find these.

 

[yorlik]

if it is 3 pins only, it is simple hall transistor; prob any model will do. like a 2n3904 transistor. any replacement will work.

 

[Monkeyleg]

A transistor is not the same as a hall sensor.

 

[yorlik]

Actually though, they are transistors. Some are sensors with more than 1 transistor inside - usually also have more legs to power the built in amps and hysterisis circuits though. With such a huge magnetic field so close, typically what is used in motor commutation sensing is dumb simple 10 cent hall transistors.

https://scholar.google.com/scholar?...ved=0CBsQgQMwAGoVChMI14HEyLyAxwIVBtOACh2Skwf3

https://www.google.com/search?q=hal...X&ved=0CDQQsARqFQoTCNeBxMi8gMcCFQbTgAodkpMH9w

Their gain is same as gain in other transistors; in hall transistor, it is how much magnetic field is required to cause conduction between emiter and collector, in regular transistor it is how much drive is required on the base to do the same. difference in part numbers for all the gidgets is gain, voltage ratings, current, etc.... since we run low voltage and current, just about any device should work, just an issue of gain. since it is sensing hi power magnets, just about any gain will likely turn it on. All magnetic fields are the same, so no difference there either. Now if we were detecting a real weak magnetic field, then a lower gain transistor may not work well enough. I had to build hall sensors to see magnets go past on a moving floor once for a Navy ship project and it had to see them almost an inch away reliably. Needed high gain puppies for that.

 

[Monkeyleg]

I realize that hall sensors are very similar to transistors, and have similar functions. I think in this application, with everything else in the P2V+ being computer controlled and very precise, it's important to get the right component.

Here's just a partial selection of board mount hall sensors: http://www.mouser.com/Search/Refine.aspx?N=10834224 If it were just a matter of slapping in a transistor that sort of worked like a hall sensor, they wouldn't need 1,027 different models.

 

[hunch]

looks like you are getting some good advice and i have to be honest, this subject is slightly over my head. burlbark may have some input about it but haven't heard from him in weeks.

 

[Monkeyleg]

Shoot. I figured if anyone would know, you or burlbark would.

What I may wind up doing is taking one I know is good from a P2V+, and measuring the voltage and current going in and coming out while in the motor while turning the magnet. Then I could remove it, wire it up, and move a small magnet toward it up to a certain distance. A refrigerator magnet is about 50 Gauss. I could then buy a some other brands that seem like they would be close and see if I can get one that's dead on. That would give me the same size, pin configuration, input and output voltage and current, and sensitivity. I wouldn't have temperature or a couple of other factors I don't believe would be issues.

 

[yorlik]

Monkeyleg, by all means get the real McCoy if you feel uncomfortable getting another hall transistor with a different part number. I can totally see where you are coming from with that idea.

I was just telling you that there is about a 95% probability that THIS application will work with ANY hall.

Of course I am not proposing you stick in a T-092 plain old transistor with a base connection! But any T-092 (I assume that is the shape you have - I did not look at your pix) HALL TRANSISTOR likely will work.

Yes, the phantom is very complex, highly computerized, but at the end of the day, the 3 hall transistors are ON or OFF - nothing inbetween. They either turn on and conduct 100% seeing a magnetic field, or they are turned off. Being so simple, anything that sees the magnetic field will likely work. That was my point.

As a side note, it is interesting to know why there are 10's of thousands of transistor part numbers.... Did you know that once a basic shape and size is designed, it comes off the same assembly line and then is GRADED in automatic equipment. Based on the alpha and beta gains, response BW, etc., a part number is assigned to it. So although one part is made over and over again, it is tested and then that same part is assigned one of 1000's of part numbers! For critical or some analog circuits, this testing saves designers lots of time by letting them now the part number they picked will work within a small range of gains and such. Most designers of analog circuits will use emitter resistors and bypass caps to allow a wide range of transistors to work anyway too. When I repair an audio radio or amp, it is often a matter of picking the right physical size device and double checking its voltage ratings and it just works.

 

[yorlik]

Another member on here said they were Allegro 1326 linear hall effect sensors. However, the sensors are stamped "1425" on the top, and Allegro says that wouldn't be one of theirs.

I'll try to help find something you can try. Did you post a picture of the hall device? if so, can you post a link to it again here?

The 1326 is really a 3 pin device - looking at the datasheet, battery power goes to pin 1 (+), pin 4 is - supply or ground, and pin 2 is the output. pin 3 is a test pin and not used for sensing use - they show it tied to ground pin. so if you can find one of these and it is same size as your's, then it prob will work fine.

I will search for something that may fit the 1425 number....

 

[Monkeyleg]

Thanks, yorlik. Hunch had posted a photo in another thread. I'll repost it below.

I've had a bit of a crash course in hall sensors the last few days. It's not just an on/off deal. Different sensors will have different release points for different amounts of magnetic force. One sensor may have a release point at 50 milli-Tesla's and another may be at 100 mT. Input voltages differ in their minimum and maximum ranges. The amount of output voltage and current can vary even with the same amount of magnetic force applied.

I emailed DJI to ask if they could just ask their engineering department or even purchasing what they buy, and then let me know the brand of sensor they use. I don't expect a reply.

 

[Monkeyleg]

Ooops. Forgot the photo.

 

[yorlik]

your a1425 in 4 pin version (again, 1 is just grounded) is available in stock for $ 4.50 from:

http://www.digikey.com/product-sear...ch-linear-compass-ics/1967232?k=a1425&stock=1

datasheet:
http://download.siliconexpert.com/p.../290/alg_/manual/2a1324-5-6-datasheet.pdf.pdf

your a1326 in 3 pin is $ 2.20 in stock here:
http://www.digikey.com/product-detail/en/A1326LUA-T/620-1433-ND/2728148

datasheet available there too.

You do NOT want the a1326 - it is an ANALOG output device, NOT an on/off device like your a1425. Analog outputs are used when one needs to make an output proportional to magnetic field - both positive and negative. NOT want motor controllers use.

I see no problem at all with the a1425. Yes, it is set for 10 gauss from the look of it and that may or may not be exactly same as your device. What happens if it turns on or off slightly ahead or behind perfect point? Not much: motor commutation tolerance is about +/-15 electrical degrees; since you have 2 pole motor, that is +/-15 mechanical degrees. Turn on and off between those points and it probably will not make any measureable difference to performance. Remember, the other 2 are also turning on/off at 120 degree increments. So a small offset from perfect won't make much effect - it certainly will not cause a cross fire with all that free space between. If I did not here back from dji soon, I would get one if it were me.

BTW, I have had halls fail from being hit and destroyed but can't say I ever had one go 'bad' in the years they have been used in servo motors that we apply and sell and service (since maybe 1985?) We have probably worked-with/repaired about 500 hall feedback motors in that time. Is yours crunched mechanically? If not, are you SURE it is bad? Usually it is a wire loose issue.

 

[yorlik]

back to the drawing board; the pix shows a SOT23 case, not a t092 or 4sip case... u need a sot23 SMD type....

 

[yorlik]

ok, now that we are passed generic description of hall transistor vs IC package with lots of stuff inside, it appears you were prob right all along: too many variables to pick one without more data.

As I tried to do so, I saw there are many variables to fill in like direction of the mag field vs transistor case and is output plain TTL 0 or 5v for on/off so has 5v Vcc supply, or is it on 6-12v and thus open collector (FET) output? Pull hi or low on + field.

I think without a starting good part number, and minus measurements on your goods ones to verify Vcc and output swing, you probably won't have perfect luck picking a replacement. Any chance you can get voltage data on the 3 pins?

Maybe even better would be to ohm them out and find the + and grnd pins - they will be common to all 3 devices. that leaves the output pin. you could then ohm to cable to find these to a) verify they are all there, and b) see what the swing is as it rotates. Then you have data to go on to pick one.

I still think you will find a mechanical issue with a solder joint or broken pcb trace they are mounted on, or ribbon connectiont issue since these things really don't have good reason to go bad.

 

[hunch]

guys i have a ton of these and what i'll do is snap pictures of multiple PCBs where these are soldered, maybe there will be a different marking on some of them and will help shed a light on this matter.

 

[hunch]

you are absolutely correct, i was able to fix about dozen of them because the trace broke or simply the solder joint broke off at the hard landing or
when gimbal was crashed. sometimes i used a thread of wire to solder from one point to another until i found a conducting pen
which made everything really easy because i just drew a line with it from point A to point B on the motors PCB and voila. all that i attempted
to fix i successfully fixed.

 

[yorlik]

http://www.allegromicro.com/Product.../~/media/Files/Datasheets/A1250-Datasheet.pdf

As I looked more, I see this is design you probably want. It takes the inaccuracy of on/off field strength out of the picture; it sees the magnet edges between n & s and latches. Now that I see this, it is same type we use on our linear motors - latching.

You also want unipolar not omnipolar; you h ave to sense just a N or S magnet and ignore the other one.

only question then is yours sensing S mag like this part or N mag like another part no....

also, you really need to at least measure the supply voltage to these; then you know if you need the one with built in Vregulator or not....

tnx hunch.

 

[Monkeyleg]

Thanks, hunch. Every one I've looked at has been marked 1425, but they are not Allegro A1425's. Those have 4 pins, where these have 3.

I measured input voltage as best I could with the sensor in place and the Phantom motors running. It varied from 3.3 to 5.5 volts DC. I can't fathom a reason for input voltage to vary, so I'm going to assume the variation as due to the firmness of my connection.

Interesting that you found broken connections in the traces. I don't have the knowledge to work on PCB's. One thing I have noticed is that I might have a good pitch PCB, but the pitch still doesn't work with that board. Swap out the motors with a good one and it works. If the windings test fine, there's nothing left except for the connections in the hall sensor circuit, or the sensors themselves. From what I've read they're fragile.

A refrigerator magnet is 50 gauss, and the magnets in the rotors are about the same strength. I'll start using that, and an input range of 3-6 volts and see what I come up with for the first test sensor. I'll also look at some of the connections in a bad motor to see what I can find.