2168 A3144 Hall effect sensor board

[Travis Schuh]

Originally Posted by craigboez

Can someone who has used the 971 board or something similar like this comment on how accurate and repeatable they are? What would you use them for and where would you avoid using them?

I'm happy to see a DIY version of what can be purchased from WCP.

We used the ones from WCP (http://www.wcproducts.net/sensors) all over our robot last year and never had an issue about accuracy or repeatability. I know the chip has a spec somewhere, I will add them if I end up finding them. I remember the spec being within a couple thou, we decided it was good enough for our zeroing needs. We used them for zeroing our arms, range limits on our arm, zeroing our shooter, and sensing state in our shooter (particularly of the pneumatics). We have used them to replace limit switches for sensing position and find them easier to integrate, more robust, and more reliable.

We have used bare sensors in the past (http://www.adafruit.com/products/158), but have found the status lights on the WCP boards to be immensely valuable (this is why we worked with WCP to bring these to market). We saved probably 10+ hours of debug time (often at the most critical times...) by having those lights on the board.

[craigboez]

Originally Posted by Travis Schuh

We used the ones from WCP (http://www.wcproducts.net/sensors) all over our robot last year and never had an issue about accuracy or repeatability. I know the chip has a spec somewhere, I will add them if I end up finding them. I remember the spec being within a couple thou, we decided it was good enough for our zeroing needs. We used them for zeroing our arms, range limits on our arm, zeroing our shooter, and sensing state in our shooter (particularly of the pneumatics). We have used them to replace limit switches for sensing position and find them easier to integrate, more robust, and more .

How did you guys mount these- just double stick tape, or did you 3d print a case, or something else?

[Travis Schuh]

Originally Posted by craigboez

How did you guys mount these- just double stick tape, or did you 3d print a case, or something else?

We bolt or pop-rivet them onto plate, with a hole cut out for the connector (or in our case, we remove the connectors and solder directly). Double stick tape like the 3M VHB could also work. We used to mount them this way before we had boards with mount holes in them. You can check out our 2014 robot CAD to see exactly what we did if you are interested in more details.

Poprivets are nice because they are quick, but we will probably move to 4-40s exclusively next year because we can replace the boards if needed. We had two minor failures last year due to one of the wires breaking off on the end of our shooter (in-proper strain relieving in a high robot-to-robot contact area) and one of the boards being mounted too close to the magnet and getting damaged due to contact with the moving part. We ended up replacing the pop rivets with 4-40s when servicing these, so it would be nice to start with 4-40s.

[Mr. Lim]

It's been a while since we've had a sensor application for stuff like this.

Quick question:

What are the pros/cons of using a reed switch for a similar FRC application?

Are they just too fragile? Even the molded-over ones?

[otherguy]

A reed switch is still a mechanical device.
My guess is that a magnetic field overcomes the force applied by some spring steel or something?

I'll walk through my rational, but state up front that I have very little experience with reed switches. I could be writing them off prematurely.

While the reed switch is non-contacting, it would still be susceptible to conditions that would cause the reed to move when the actual physical component it is mounted to has not (i'm thinking shock event).

The hall effect sensor on the other hand has no moving parts (it may be more accurate to say the MEMS components that do move have such little mass that they won't accelerate significantly do to shock). So the only time they should indicate a state change is when the magnet (and the component its connected to) actually moves away from the sensor.

That said... looking through digikey, there are some pretty tiny surface mount reed switches. It might be a viable option. They are in the same price range as the hall effect sensors I used.

At the end of the day the hall effect or reed switch is just another tool in the toolbox for us. It's not going to be the end-all sensor. I like to have options on hand so that if we have ideas we can prove them out quickly. Hopefully they end up on the field, but if they don't it was a pretty small investment. I ordered electrical components off ebay, with the custom PCBs, these things come in at around $2.50 a board.

[otherguy]

Boards are in, populated, and tested out good.

[Lialovefood]

Originally Posted by Travis Schuh

We used the ones from WCP (http://www.wcproducts.net/sensors) all over our robot last year and never had an issue about accuracy or repeatability. I know the chip has a spec somewhere, I will add them if I end up finding them.

I know this was from a while ago, but did you happen to find the spec sheet for this?

[Travis Schuh]

Originally Posted by Lialovefood

I know this was from a while ago, but did you happen to find the spec sheet for this?

I looked again and asked around, but didn't find it.

The best I can find is that the position that results in switching is most accurate when moving the magnet sideways in front of the sensor, rather than closer/further (see page 5 and 6 of the appilcation notes, found at http://www.melexis.com/Assets/Hall-A...de--3715.aspx).