Hall Effect Sensors

[BitTwiddler]

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.

[Gregor]

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

[protoserge]

A photo is worth at least 836 words...

[Brandon Zalinsky]

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.

[Ether]

Originally Posted by stinglikeabee

A photo is worth at least 836 words...

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

[protoserge]

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


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

[Katna.Grace]

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.

[electroken]

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.

[Ether]

Originally Posted by electroken

It gives us a nice, clean 27 pulses per output shaft revolution

How are you decoding the signal?

[electroken]

Originally Posted by Ether

How are you decoding the signal?

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".

[Ether]

Originally Posted by electroken

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".

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?

[BitTwiddler]

Originally Posted by electroken

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.

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?

[MrForbes]

Originally Posted by BitTwiddler

3. Do you have any data on how it performs on chain sprocket teeth?

.....steel? aluminum?

[Kevin Sevcik]

Originally Posted by MrForbes

.....steel? aluminum?

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.

[BitTwiddler]

Originally Posted by Kevin Sevcik

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.

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!