Electronic home switches made easy!

[TarHeelTom]

I've nothing against hall effect switches, but must point out one possible failing here.

This design is fine for a homing switch, but has a limitation when used as a limit switch.

Good safe design on limit switches suggests that ALL the wiring on limit switches and the emergency stop switches be wired in series. This means that a broken wire or a loose connection anywhere in the system activates the emergency stop feature.

Don't remember all the references (or even the correct wording) here, but there is an (probably an OSHA) rule that requires a machine to be able to shut itself down and cease all movement (including the spindle rotation) when certain events might occur.

There is a lot of wiggle room in this rule. For instance, a small mill, like a Sherline, for example, has steppers that are weak enough so that they just stall when the physical limits are reached. So there are no limit switches installed, and generally not even a physical eStop button.

As machiines get bigger and heavier and faster and more powerful, the rules should be read more as hard guidelines.

As I have absolutely no idea what type of machine any of you are building, I can make no specific suggestions. But do attempt to wire your limit switches in series whenever possible.

[GEBrown]

Al,
The wires are black, light blue, dark blue, and red as you can see in the pictures.
There seems to be a sensor at each end of the slide.
I did search the website of the manufacturer, but couldn't find anything.
Thanks!
Gary

[crob09]

Hey Guys,
Now I'll admit that I haven't read all 36 pages of this thread, so if my question has come up before, please excuse my laziness and point me to the appropriate post.
I bought a linear slide table that has hall effects sensors already installed, but no documentation about which wires are +5v, grnd, nor feed. How does a guy with only a VOM, a 5 volt DC supply, and an LED go about detecting which is which?
Thanks very much in advance,
Gary

Look for the resistor!!

The hall effect sensor needs to be pulled high or low, at least knowing where the resistor is helps you find the Output pin.

Also the Hall effect sensor is more for position sensing not limit sensing, Opto's are great and a mechanical switch works good too.

Hope that helps!

[GEBrown]

crob09
If by "look" you mean visually look, the pictures show everything I can see. The sensor is built into the table and I'm leery of pulling up on the sensors themselves for fear of impeding the travel of the table.
Now if you mean "look" with a VOM, I'm all eyes (ears).
I use optical switches normally, but since these are built in, if I could learn how to wire them into a Gecko G540, I'd have another option to look at. At least I will have learned something new.
Thanks all.
Gary

[Pleine]

I have ordered the wrong sensors by mistake, and I am really happy about it!

I have ordered the SS411A, which is the bipolar version of the hall sensor. In other words, the switch needs a S > N magnetic field transition to work. So instead of presenting the S face of a magnet, I presented the side of a tiny (4x4x2mm) NdFe magnet.

With a SS441A, the whole magnetic field has to move by the sensor, and for a small mill like mine, this costs valuable millimeters. In my setup, the S > N transition takes place in 2mm. And that is perfect for me.

Just wondering if any of you electronic gurus see any downside using a SS411A?

Thanks a ton,
Pleine

[crob09]

Yup I mean look for the resistor.

Don't pull on things, but find the resistor and you'll find the output wire, it's that simple.

Opto's wire the same way a mechanical limit is wired, Gecko drivers should have silk screen to help with that step.

[Stevos758]

Alright got mine working. Almost. Everything is repeatable except the z axis. I slowed it down to 20% speed. Still position is off by a mm or so. Any ideas as to what is happening or what I can try.

[hollisin]

Steve,

my homing settings are
X 20pct of 750 = 150, air gap is 1/16
Y 10pct of 750 = 75, air gap is 1/16
Z 60pct of 31 = 18, air gap is 1/8

Haven't checked it in a while but was only .001 sometimes, mostly zero.

picture is my Z axis homing setup. The white disk has the magnet in the center flush to the surface, the black speck in the very center of the pic is the sensor. This pic is after a Z homing command.

Move each axis to near home press the arrow/pgup/dn key to move away at 100 pct, look at the velocity reading in mach3. Look at the pct in homing page.

I did use 1/8 super magnets for accuracy, seemed to pay off.

Jack

Alright got mine working. Almost. Everything is repeatable except the z axis. I slowed it down to 20% speed. Still position is off by a mm or so. Any ideas as to what is happening or what I can try.

[Stevos758]

My bad. I meant x axis. I miss typed on my phone. I'll get a pic of my setup later.

[Stevos758]

Steve,

my homing settings are
X 20pct of 750 = 150, air gap is 1/16
Y 10pct of 750 = 75, air gap is 1/16
Z 60pct of 31 = 18, air gap is 1/8

Haven't checked it in a while but was only .001 sometimes, mostly zero.

picture is my Z axis homing setup. The white disk has the magnet in the center flush to the surface, the black speck in the very center of the pic is the sensor. This pic is after a Z homing command.

Move each axis to near home press the arrow/pgup/dn key to move away at 100 pct, look at the velocity reading in mach3. Look at the pct in homing page.

I did use 1/8 super magnets for accuracy, seemed to pay off.

Jack

Let me be more clear.

All axis home properly, All axis except X are perfectly repeatable. I am picking a spot on the opposite side of the table and using G00 to move it there to visually check accuracy. The Y axis movement ends up going to the same spot every time. The X is off by a MM or two in random directions each time? It will never go back to the exact same position even though I keep using the same G00 command(examle G00 y-500 x-320)

The only thing I can possible come up with is there is a capscrew right next to my Hall switch. Could this somehow throw off the magnetic field?

I cant wait to get this working! Hopefully someone here can help.

[nlancaster]

Super magnets actually make the HAL sensor work less reliably.

[Stevos758]

I see. I'll see if a smaller or regular magnet solves the issue.

[ger21]

I use a strip magnet, which is very weak. It needs to be very close to the sensor (<1mm), but works very well. Also, the sensor detects the magnet from the South pole I think. The strip magnet works well for this, as one edge is S, and the other is N.

[Stevos758]

I did get it working. I needed to use 550ohm resistors instead of the 2.2k. They work fine now.

I just need to figure out how I want to perm mount them now.

[jsantos]

I thought that I'd share what I did for my hall effect sensor. After a misstep and a lot of research, I ended up getting my hall effect sensors from eBay for $0.99 a piece. Do a search for "Arduino hall effect sensor" to find them. The sensor is a 3144 sensor mounted on a PCB, complete with LED and resistors. See the attached photos.

1. Photo 1 - On the left is the first sensor I used. This is a Hamlin sensor and IT DOES NOT WORK. In the middle is the sensor that I got from eBay and on the right is the eBay sensor encased in plastic and epoxy.

2. Photo 2 - Shows the sensor mounted on my machine, lighted up.

[DaQue]

What kind of repeatability do you get?

Sent from my Nexus 5 using Tapatalk

[Stevos758]

I thought that I'd share what I did for my hall effect sensor. After a misstep and a lot of research, I ended up getting my hall effect sensors from eBay for $0.99 a piece. Do a search for "Arduino hall effect sensor" to find them. The sensor is a 3144 sensor mounted on a PCB, complete with LED and resistors. See the attached photos.

1. Photo 1 - On the left is the first sensor I used. This is a Hamlin sensor and IT DOES NOT WORK. In the middle is the sensor that I got from eBay and on the right is the eBay sensor encased in plastic and epoxy.

2. Photo 2 - Shows the sensor mounted on my machine, lighted up.

Very nice. I cant quite read it but is it a 681 ohm resistor? That should be close enough to my 550k ohm correct?

I think I will order some. Cant hurt to try I guess.

[jsantos]

What kind of repeatability do you get?

Sent from my Nexus 5 using Tapatalk

The sensors are incredibly accurate and repeatable. I've got an x- and y- fence mounted on my machine and the coordinates of those fences have not varied in the couple of months that I've been using the machine. What I find really amazing is that the DRO readings on those fences have stayed the same, down to the last 4 digits. And I'm using metric!

So when I'm cutting something, I just mount the material flush to the fences and I don't have to look for the x- and y- edges of the material!

[jsantos]

Very nice. I cant quite read it but is it a 681 ohm resistor? That should be close enough to my 550k ohm correct?

I think I will order some. Cant hurt to try I guess.

Impressive eyes! Yes, it's a 680-ohm resistor.

[Stevos758]

The sensors are incredibly accurate and repeatable. I've got an x- and y- fence mounted on my machine and the coordinates of those fences have not varied in the couple of months that I've been using the machine. What I find really amazing is that the DRO readings on those fences have stayed the same, down to the last 4 digits. And I'm using metric!

So when I'm cutting something, I just mount the material flush to the fences and I don't have to look for the x- and y- edges of the material!

Awesome! My hot glued on ones worked ok but these look nicer and will be easier to handle. Did you just epoxy them on?