Electronic home switches made easy!

[RomanLini]

Thanks for the feedback guys! Hope more people will use these nice accurate no-moving-parts sensors.

Since my last couple of posts were lots of words and test results, here are a couple of "easy" diagrams;



Inside the SS441 hall switch
The "brain" part is powered by the + pin; 4v to 30v, but +5v is a good enough choice. The brain does stuff like the temperature compensation, and ensures clean fast switching at the correct magnetic field strength.

The "switch" part behaves basically like a normal switch. The switch is actually part of the silicon chip inside but we use it just like a normal switch; one pin is connected to ground, the other pin is the Output pin. Note! Because it is a silicon switch (FET) it is limited to only switching small currents (less than 20mA).




Connecting the hall switches
The +5v and ground are supplied from the controller, and the same +5v and ground can connect to all the hall switches on your machine.

The output from a hall switch is connected back to a "home" or "limit" input on the controller.

Some controllers have an internal pullup resistor, or you can select an internal pullup resistor. If not, then it is easy enough to connect an external pullup resistor, a value of 2200 ohms (2.2k or 2k2) is fine. Note! It should not cause a problem if you add the resistor when it is not needed, so if in doubt you should add the resistor.


If anyone has specific info on a controller and how it would connect to these switches please post any info you have! I built my own controller so I am not familiar with all
the common controllers and their specific setup.

[RomanLini]

This has been use before, but like you say not much imformation on them any were, that is because they have very limited use on metal cutting machine, they would be ok on wood working machines,were you only have wood dust to deal with

The magnets get covered with metal chip, so you know what happens next, & there's no way to stop this from happening
...

That is a good point mactec54, these sensors are not very useful in a machine that will be cutting steel or ferrous metals.

But I think they are ideal for router type machines cutting wood, plastic, aluminium. Even with the small chance of getting metal shaving stuck to the magnets (which would change the sense distances) they are still more accurate and reliable than any type of mechanical microswitch.

I want to make that point again that the best type of magnet for these sensors is a small one with a weak magnetic field, this gives closer sensing and better distance accuracy. Small weak magnets are also less likely to collect trash, and can be designed for easy cleaning as only one end of the magnet needs to be accessible to trigger the hall switch, the rest of the magnet can be buried inside a wood or plastic block.

[RomanLini]

Making mounts for the hall switches

I know people don't want to go sticking sensors all over their machines with silicone (like my test setup above!) so this evening I put aside some hours to make some mounts out of clear acrylic (some scrap I had lying around).

I roughed out some simple designs that can be cut out easily from 10mm (3/8") acrylic and from 6mm (1/4") acrylic.



This mount above is 10mm, and has a deep pocket to hold the wiring, solder connections etc. There is also a shallow pocket of 2mm depth to hold the hall switch, to it is close to the surface and allows the magnet to come close to the hall switch.

One drawback is that it needs to have a small hole drilled to insert the wires, and a special height pocket for the hall switch so there are 3 heights to be cut. Another drawback is that it needs more epoxy to fill it, and people using 5-minute araldite would be better with a small pocket that needs less filler.



Above is my second design, I tried to simplify the mount to the simplest features possible. It is made from 6mm acrylic and only needs one height cut, for the shallow pocket and screw area are both cut about 2.5mm deep.

It only needs a small amount of filler epoxy, and is more compact in general. The down side is that it is fiddlier to solder the wires because it is smaller and it is not as sturdy as the 10mm mount.



Above is a (fuzzy) photo of the 2 mounts, on the right the 10mm mount shows the hole drilled for the wires, and the deep pocket for the soldering, and uoi can just see the tiny shallow pocket for the hall switch.

On the left is the much simpler mount, with just one height cut for the pocket and screw recess. The wires are inserted by the simple slot.

Below shows that I made 3 of the smaller mount, because these are smaller than the 10mm mount I think they will be better for my small machine.



Next I soldered the wires to the hall switches and inserted them into the mounts. I added 2700 ohm resistors directly on the hall switches, there is room in the mounts to do this and it means I don't have to add resistors later.

The hall switches were quickly glued down with a little spot of superglue.

Then the wires were sealed with a hot melt glue gun so the epoxy won't leak out before it sets! You can also see where i glued the mounts onto a flat piece of plastic to hold them neat and level while pouring the epoxy. I put an extra glue blob on the wires too to hold them steady.



I used a shielded 2-core cable for the larger mount. This is cheap microphone cable, red+white+copper shield. It's quite tough, very flexible, and the shield is nice to have on longer cable runs.

On the small mount I used 3 wires, red, black and white. This will only have wires about a foot long so the shielding is not needed and was easier to solder in the confined space of the small pocket.

The epoxy is setting at the moment, i'll post photos of the finished mounts tomorrow.

[DIYaholic]

RomanLini,
Too bad, you already posted the instructions for these swithes. People would've had to buy them from you! I see people (all thumbs, like me) willing to buy them from you anyway. You should come up with a price and offer them for sale!
BTW, great job documenting the design and assembly!

[RomanLini]

Prototype mounts are finished!

I let the epoxy cure for about 14 hours on my hotplate at 45 degrees C.

The epoxy had a drop of red colour in it to make it more visible in the photos, but only a small drop because I wanted the parts inside to still be visible.



The mounts were tacked down to a piece of plastic with hot melt glue, this will break straight off later.

Below you can see the small mount leaked a bit! When I sealed the 3 wires with the hot melt glue it didn't get between the wires, so it slow leaked there. I countered by topping it up a bit more and because the mount was warm (on the hotplate) it hardened up faster than it leaked so it wasn't a big problem.

The epoxy looks a lighter colour red in the small mount because it is much less thick.



Below are the 2 finished mounts after breaking off the hot melt glue. If you chill the mounts in the fridge for a while the hot melt glue is brittle and breaks off pretty clean. Don't mess with the hot melt glue if it is warm, it just smears everywhere!



Both mounts are successful and usable.

Below you can see the large mount with the round drilled hole for the cable was a better result (cleaner, physically stronger, no leaks) than the simple slot used on the small mount. The round cable was better than 3 wires, and the round hole works better than the simple slot.

The epoxy has nicely filled the tiny void around the cable in the round hole. The cable has no change in flexibility where it exits the mount, so there is no evidence of epoxy being sucked into the cable.



The last photo below shows the volume of epoxy used. The larger mount used 4 times as much epoxy, and you can see a slight sink in the top surface where the deep pocket of epoxy has contracted as it cured.

The small mount didn't have this problem because it was very shallow.




Conclusion

Both mounts came out good. Apart from the downside of the larger mount being well... larger! it was easier to solder, supports and seals the cable better, mounts the sensor at a known height and is overall more rugged and less likely to break.

The pocket does not need to be so deep, this was obvious on the small mount which had a 2.7mm deep pocket. So the large mount could just have a shallower pocket than the 8.5mm deep pocket I used here, and this would fix some of it's issues.

Holding both mounts in my hand, the larger mount feels much better, sturdier, and overall seems like a much better design.

[RomanLini]

RomanLini,
Too bad, you already posted the instructions for these swithes. People would've had to buy them from you! I see people (all thumbs, like me) willing to buy them from you anyway. You should come up with a price and offer them for sale!
BTW, great job documenting the design and assembly!

Haha! Nah this was never meant to be for profit! Open-source is for giving back to the community, I like to provide something back so the net total of my participation here is positive.

From a manufacturing point there's probably 15 minutes of soldering and fiddly work with each mount, which is perfectly ok for open-source building them yourself but with the high labour costs here in Australia it just wouldn't be worth producing finished units to sell.

But, if enough people show an interest I can improve the mount design a little and cut 100 or so mounts in 10mm clear acrylic, then supply them in kit form with;

3 mounts
3 hall switches
3 resistors
?? yards of shielded cable

I have a ton of commercial projects on this year so I really am not that fussed about trying to make money out of this. Maybe if someone else wants to make kits (which is basically a CNC machining job) I would be happy to act as unpaid advisor and pass on ideas for improving the mounts etc, although I would like to see it stay within this thread so it would acknowlege my input, and everyone else's input (open-source remember).

[jalessi]

RomanLini,

Have you tested the repeatability yet?

Very nice work,

Jeff...

[RomanLini]

Hi Jeff, yep see posts #8 and #9, the figues there are repeat tests.

As far as I can tell the sensors repeat better than 0.01mm (0.0004") but my machine coord system only reports in 0.01mm resolution, and once my machine gets warm my leadscrews grow 0.02mm in length or more.

Based on my Y axis where the sensor is on the motor end of the leadscrew (so it has minimal leadscrew thermal expansion), the repeatability seems around 0.01mm and is probably better than that.

If someone has a machine with a low lead-per-turn screw (like 1/2" 10) and heavy high friction axes, (like a milling machine) I'm happy to mail them a sensor and they can test repeatability.

[jalessi]

RomanLini,

I should have read the entire thread, sorry I missed several posts.

Excellent repeatability, cant ask for better than that.

Thank You,

Jeff...

[eloid]

question are the very smalll ear earth magnet too strong for this?
would they still work? any feedback on using them?
the resistor is for led or switch bounce pull up?
or the r values changes the gap setting?


do u have a video with it working with the plastic mounts....the led goes on when switch triped?
the new mounts do they use the led?

[RomanLini]

1 question are the very smalll ear earth magnet too strong for this?
would they still work? any feedback on using them?
2 the resistor is for led or switch bounce pull up?
3 or the r values changes the gap setting?
4 do u have a video with it working with the plastic mounts....the led goes on when switch triped?
5 the new mounts do they use the led?

1. Possibly, the stronger magnets i tested triggered the sensor from further away. There is no benefit to that. Because of the higher strength magnetic field everything is increased; sense distance, hysteresis distance, error.

My thoughts for "perfect" magnets would be small weak magnets. They pick up less crud and will give better accuracy and repeatability.

Even the weak bar magnets I used trigger the hall switch from 5mm to 7mm away, if I had used weaker magnets still that triggered it from say 3mm away the accuracy would be doubled.

2. The resistor is for "pull-up" use, it makes the sensor output a +5v when no magnet is near, and output 0v when magnet it near. It turns the sensor into "logic-level" output that can be tied directly into any logic input and means you never have to fuss with resistors later.

3. No, the resistor does not change the gap setting.

4. Sorry I don't have a good video camera right now, I will take a video at some point in the future.

5. Thank you, that is a REALLY COOL idea! If the LED is soldered onto the sensor and clear plastic is used for the mount then it will light up when the magnet is near!

Apart from the cool fun factor that would be really valuable for setup and fault finding and would really improve the design!

[eloid]

1. Possibly, the stronger magnets i tested triggered the sensor from further away. There is no benefit to that. Because of the higher strength magnetic field everything is increased; sense distance, hysteresis distance, error.

My thoughts for "perfect" magnets would be small weak magnets. They pick up less crud and will give better accuracy and repeatability.

Even the weak bar magnets I used trigger the hall switch from 5mm to 7mm away, if I had used weaker magnets still that triggered it from say 3mm away the accuracy would be doubled.

2. The resistor is for "pull-up" use, it makes the sensor output a +5v when no magnet is near, and output 0v when magnet it near. It turns the sensor into "logic-level" output that can be tied directly into any logic input and means you never have to fuss with resistors later.

3. No, the resistor does not change the gap setting.

4. Sorry I don't have a good video camera right now, I will take a video at some point in the future.

5. Thank you, that is a REALLY COOL idea! If the LED is soldered onto the sensor and clear plastic is used for the mount then it will light up when the magnet is near!

Apart from the cool fun factor that would be really valuable for setup and fault finding and would really improve the design!

try a blink led.... ie red or blue?

if some where in the sensor there was a cicrcuit to change the gap range it would be cool
ie a pot.... for gap triming or adifferent hall sensor that has that feature