Hall Effect Sensors
 

Where could I find FRC legal hall effect sensors that would work with a PWM cable? I've found this and this. Any recommendations for use, mounting, wiring, sourcing and buying? Also, how could you code one in Java or C++?

Re: Hall Effect Sensors
 

Custom Circuits are legal. Make sure all wiring is within the rules and the power is provided as legally required.

R39, R47, R54, R58, R69, R72 are a few.

We have used a hall effect in the past. I will direct some additional help to this thread.

You can code in anything. If you are running your robot using LabVIEW, I don't see why you couldn't do it in there too.

Here's an email I got from another mentor:

Re: Hall Effect Sensors
 

Team 1726 has used both kinds of magnetic sensors with good results.
The gear tooth sensor will detect the presence of ferromagnetic material (such as a steel sprocket) passing by whereas the magnetic switch will require a magnet (North turns it on - South turns it off).
The magnetic switch will require some additional components but the gear tooth sensor is ready to use with a Digital IO.
The magnetic switch is a lot cheaper to purchase and is also available at Sparkfun Electronics.
Also, we found the output of the magnetic switch to be somewhat noisy electrically but using the Low Pass filter from the PID library can reduce the noise.

Re: Hall Effect Sensors
 

We used the hall effect sensor in your second link last year, combined with a 22 tooth steel sprocket on our shooter, with no issues.

Included below are some photos from our Facebook page showing the mounting.

https://fbcdn-sphotos-f-a.akamaihd.n...92706845_n.jpg

https://fbcdn-sphotos-e-a.akamaihd.n...43415980_n.jpg

Re: Hall Effect Sensors
 

A photo is worth at least 836 words...

Re: Hall Effect Sensors
 

We tried to use Hall Effect sensors to detect the bump last year, and it did not work at all for us. They were so finicky that if they were 1/64 higher or lower than the 1/8" mounting window, they wouldn't work.

Re: Hall Effect Sensors
 

Hey! Finally somebody who knows where the "macro" button is on their camera :)

Re: Hall Effect Sensors
 

Oh no! I forgot to put the Gaussian blur effect on! :D


I feel your pain with the atrocious camera phone shots trying to clarify something.

Re: Hall Effect Sensors
 

We (3132) are using hall effect sensors with a buffering circuit this year. We developed them in the off-season for our 2012 shooter wheels.

We use Hall Effect sensors from RS (http://australia.rs-online.com/web/p...-ics/7384743/).

We are mounting the board flat underneath our shooter wheel, and 'hanging' the magnets down off the wheel. The magnets are epoxied into a piece of aluminium hex stock that was turned to a taper and had a hole drilled in it for the magnet. A thread was then tapped into the other end of the piece, to mount it on the end of the bolt holding the wheel on.

When mounting them, make sure that the sensor itself can't move, so that it can't be sheared off by whatever it's measuring or drift away from the magnet.

I'm attaching a picture of the board, and a picture of our magnet mounts (before the pcb is attached), as well as the schematic for the buffering circuit. Let me know if you have any questions.

Re: Hall Effect Sensors
 

A useful gear tooth sensor that wires directly into a digital input is the Allegro Microsystems ATS667LSG. We like to use them when we need speed information but not direction information and we don't need the highest resolution. We also like that they're $6.

In the photo below an ATS667LSG is mounted to a carrier board and installed in the side of a Cim-u-lator gearbox, with its face about 0.03" from the output gear. It gives us a nice, clean 27 pulses per output shaft revolution. The sensor on top of the right motor is just posing for the photo.

Re: Hall Effect Sensors
 

How are you decoding the signal?

Re: Hall Effect Sensors
 

Nice find! A few questions.
1. Where did you purchase them?
2. Did you wire them with the bypass and lowpass capacitors?
3. Do you have any data on how it performs on chain sprocket teeth?

Re: Hall Effect Sensors
 

.....steel? aluminum?

Re: Hall Effect Sensors
 

Steel. Gear Tooth Sensors have an embedded rare-earth magnet along with a hall effect sensor. They detect a change in the magnetic field that you're not going to see with a non-ferrous target.
EDIT: Also, Digikey has 22,690 in stock. Better order quick before they run out.

Re: Hall Effect Sensors
 

I think Jim was yanking my chain (also non-ferrous) for not being more specific.
Thanks for the source info though. We'll get our order in ASAP!

Re: Hall Effect Sensors
 

1. Digi-Key (hurry... only 22,000 left!)
2. The capacitor hiding in the epoxy is a 0.1uF 50V ceramic across power and ground.
3. We haven't tried reading sprocket teeth, but I would expect them to work well with steel sprockets and a small air gap.

Re: Hall Effect Sensors
 

That's a good question. I told the student writing the code what to expect for a signal, and he said "Yeah, I got this".

Re: Hall Effect Sensors
 

The decoding method makes a big difference in the quality of the signal, especially at high speeds (depending in the method used).

Could you ask him to join the discussion here?

Re: Hall Effect Sensors
 

It was a serious question, Dave, because the sprocket is aluminum and I thought they only worked on ferrous teeth.

Re: Hall Effect Sensors
 

Hi Katherine,

We (FRC #4774) are going to use the same sensor boards! Thanks for making them open for others :D

We (FRC #3132) *1 forgot to include the value of T1 on the schematic. It is a 2N2222 NPN transistor, a TO92 package. Part of me is wondering if we can make all components sit flat so the board could be laminated in a future revision?

BR,

Adam

*1 (Yes, I am a mentor for two teams) :)

Re: Hall Effect Sensors
 

Hi Adam, we've just ordered magnets from a company in Sydney: http://www.magnet.com.au/neodymium_r...ts#discs_small

If I'd known that you were going to use the same sensors I'd have ordered enough for 4774 as well. We may have extras, so let us know if you need some.

Of course, as you know, DealExtreme also ship neo magnets to Australia.

Re: Hall Effect Sensors
 

Team 2729 also is selling some boards they designed and made that are quite nice and that wire right up to the sidecar with a PWM cable; proceeds fund their team. See http://www.chiefdelphi.com/forums/sh...2&postcount=14.

We glue a small diametrically magnetized ring magnet (K&J Magnetics R424DIA) on the back shaft of a BaneBots motor to drive it, 'tis robust. See http://www.chiefdelphi.com/forums/sh...d.php?t=112294

Re: Hall Effect Sensors
 

Electrotoken, am I right in thinking that the magnets in the hall effect sensor in the ATS667LSG detects the disturbances in the fields from the magnets mounted in the sensor package as the steel gears in the gearbox rotates through the field? Did you just connect it into one of the digital inputs on the Digital Sidecar? The datasheet does not seem to show any sort of calibration. Did you just stick it on, connect the wires and run?

Re: Hall Effect Sensors
 

Your thinking is correct in that the magnet is buried in the sensor. I don't know if the 0.1uF cap I have between power and ground at the sensor end is strictly required, but it makes me feel better.

It really is as simple as wiring into the digital sidecar and counting pulses. We used two of these last year and will be using three this year.

Re: Hall Effect Sensors
 

Do you know if you were able to sense direction with this sensor?