Magnetic Strength Sensor
JonnyMac
Posts: 9,102
I took my friend, Rick (Paintball Mini-gun) Galinson, to dinner for his birthday the other evening. He asked me if I new of a sensor with an analog type output that corresponds to the strength of a magnetic field.
I don't know of such a device.
I'm hoping some of you might and willing to share your thoughts.
I don't know of such a device.
I'm hoping some of you might and willing to share your thoughts.
Comments
Google also finds Analog/PWM/SENT output ones, like SiLabs Si721x series, that look easy to talk to.
-Phil
There is a great range of choice, when it comes to linear hall-effect sensors, from AllegroMicro,TI and other companies.
A bit of experiment will be needed, in selecting the proper (neodimium?) magnet/sensor pair that best matches the sensitivity range of mechanical measurement your friend wants.
In the same line of thinking, but not fully OT; since actresses and actors often use ear-phones, have ever you heard/thinked about using something like this:
iplab.cs.tsukuba.ac.jp/paper/international/ando_uist2017.pdf
They are talking about tiny barometers (Bosch BMP280) and commercialy available canal-type ear-phones (Panasonic RP-HJE260).
At least they seem to be easier to wear, different from having to glue something to the actor's face, near the muscles or teeth, like magnets or flexible piezoelectric sensors.
The main problem I can foresee with air pressure-based sensing, is that they will also catch the swallowing movements that happen, for example, when we compensate for changes in atmospheris pressure, so as to avoid feeling pain in the ears, though the authors of the study seems to didn't tested that possibility.
Henrique
AS5145
Not exactly what you are looking for but could be used to determine what angle the jaw is at.
Mike
This is the type of sensor that Diver Bob uses to sense the position of the legs on his hexipod bot. He and Duane Deign have developed Prop drivers for this type of chip that uses a magnet with a magnetic field orentation across the magnet rather than lengthwise to the magnet. Angular position results can be quite accurate.
Jim
I appreciate everyone's input. Keep in coming!
Maybe Beau will chime in.
TI makes an inductance to digital converter chip LDC1000, which would be any easy path for this but probably overkill.
That sounds useful, like a LVDT approach where 2 or 3 coils are coupled.
Some use A and !A sine drive with a null at centre balance, and others use COS and SIN, and give 45' phase shift at balance.
That would be contactless, and could be quite light, and should have good noise immunity and be easy to set up, with a range related to coil size.
I wonder if a hinged PCB with Printed coils could be made good enough here ?
or, maybe a small stepper motor can be connected as a sensor/generator, and give useful enough velocity related feedback to sync mouth movement ?
There are arrangements of coils that bring them into good null where the fields cancel out in the receiving coil so that small disturbances can be easily detected. Similarly for a single excitation coil and a passive second element.
Here is a nice article from Digikey on the differences and applications of Hall effect vs magnetoresistive sensors.
-Phil
Perhaps, but this sort of application is less price sensitive. Something that is reliable is worth a lot.
There is also this device LDC0851 - somewhat lower cost.
-- that has a compare out, but seems to run 2 coils, alternating for ~ 4318 (4096?) counts each. A comparator on each coil could feed to a Prop Freq Ctr, to use this for analog compare use.
the simple compare out could drive a LED to confirm operation.
addit: another approach, could be to use the nifty small SOT353 74AHC1G42xx series
- use that to make a LC Oscillator, in the MHz region, and feed the Osc/2^N into a prop pin, to measure frequency (eg 15M/2^14 ~ 1kHz divided) - pretty much the same idea as the TI parts, but much cheaper.
Two could make a differential design. An 80MHz Prop would resolve to > 16 bits on that ~ 1KHz/1ms update rate. Measure over 16 cycles/16ms, and it's ~ 20 bits.
EXAMPLE:
Magnet 10mm × 6mm ferrite cylinder
Distance from magnet to sensor From 20 mm to 3 mm linear.
...that is one interesting device.
Thanks.
Nice looking part, but does need a bulky magnet. I'd guess any magnet will 'work', but their linearity would vary - for this, that may not matter too much.
Neodymium is 8x stronger at same volume (though FE is 40% lighter in weight):
That this tiny at 40cent each should work, it got a step-in to better secure it to a holder:
https://www.kjmagnetics.com/proddetail.asp?prod=GD05H1&cat=185
There is a calculator on the right side http://www.ti.com/product/drv5013,
and using the above magnet 0.15" & 0.1" grade 42:
at 20mm = 0.62 mT
at 5.3mm = 19.93 mT (the max for A1 version)
at 3.9mm = 39.25 mT (the max for A2 version)
at 2.7mm = 79.77 mT (the max for A3 version)
at 1.7mm = 160.12 mT (the max for A4 version)
Ferrite or neodymium magnet pro/cons:
https://www.supermagnete.de/eng/faq/Should-I-buy-a-ferrite-or-neodymium-magnet
Though I haven't toyed with one for years, an analog Hall effect sensor indeed falls into this category. The threshold digital output typical of Hall devices is added to make them useful in more applications; internally they are all analog.
I'd worry some about where to put the magnet(s). I imagine Rick has talked to the stunt coordinator for his/her input on possible use of magnets placed inside the actor's mouth. Maybe sensors for use with a much lower Gauss magnetic strip (therefore not swallowable) could be used. Anyway, an interesting project.
https://www.magcraft.com/
He uses them in a specialty scale designed for shooting enthusiasts who reload ammo. Funny thing is that the scale is controlled by a BASIC Stamp 1 (it's still useful).
https://www.webmd.com/parenting/baby/news/20041026/swallowed-magnets-are-dangerous
-Phil
Unless the magnet was firmly embedded in a dental appliance, I would not recommend that route.