Electronic home switches made easy!

[RomanLini]

Mounting block with LED

I got a couple hours free today so I drew up my improved mount block design with the added LED indicator.

This diagram should have enough info, dimensioning etc for anyone to make these mounts. Sorry I don't use any standard CAD program so I can't offer CAD files or DXF, my machine works direct from Corel so I just work in 2D or write C code to do complex 3D cutting. Maybe someone who uses the popular CAD program (I don't even know which CAD program is most popular here!) can whip up a CAD design.



Cutting info.
The mount is cut from 10mm (3/8") clear acrylic, using a 1/8" (or 3mm) diameter end mill capable of plunge and cutting the full depth of the sheet.

1. Cut the shallow pocket 24x11 mm (2mm depth)
2. Cut the deep pocket 20x11 mm (to a total 7mm depth)
3. Cut the screw relief step, 30x10 mm (4mm depth)
4. Cut the 2 screw holes or elongated slots as desired
5. Cut around the mount 30x25 mm (to remove it from the sheet)
6. (in drill press) drill a 3mm hole for the wire (and deep enough for the LED if LED is to be used).


Mount design inprovements

This mount has a few small improvements from my design further up the page;
1. larger and thicker screw area for strength
2. shallow area for Hall switch is full 11mm width now; for better epoxy flow and less epoxy shrinkage there around the sensor
3. LED hole, is just a continuation of the wiring hole
4. deep pocket is not quite as deep now; saves epoxy, stronger, less shrinkage

At this point I can't see how to improve it much. Apart from redesigning it for special needs like miniature size, or changing the screw mounts to suit the equipment it looks pretty much done to me.


How the LED works

The design uses a 3mm LED, this is the smaller size (other popular size is 5mm). The 3mm size has become the most popular size these days and should be available anywhere cheap.

It won't matter too much which LED colour you choose, you can still use the same resistor values. You can even use different colour LEDs on different axes.

It would be best to use a "high intensity" LED, these cost maybe 50 cents more each but are MUCH brighter so will be much more visible when buried down between moving parts of machinery.

The resistor values shown below only run about 4mA through the LED, so the old style LEDs will not be very bright at that current but the new high intensity LEDs will be very bright at 4mA as they are really "high efficiency" as well as high intensity.


Other mount materials

If you want to use a different plastic than clear acrylic, like you may choose a high strength plastic like Delrin or just use plastic you have handy then it will be more difficult with the LED.

In the clear acrylic, the LED will light up the whole mount and be very visible.

But if using a black or coloured plastic, you have 2 options;
1. drill deep enough so the end of the LED actually comes out of the mount (this requires sealing before pouring epoxy)
2. drill ALMOST through, so there is only a thin skin of plastic in front of the LED

I would try method 2 first! Most plastics (even black) are quite translucent when they are very thin like 0.5mm (0.020") and the high intensity LED will shine out easily. If not, then just continue the hole all the way through.

[Ernie34]

Guess what I am doing tomorow! Awesome job!!!!!!

[RomanLini]

Wiring up the LED mount

Below is the wiring diagram for the new mount, the left version is just the hall switch and a pull-up resistor. The version on the right has an added LED and one more resistor. Both use the same mount block, so the LED is optional.





Construction method;
1. trim and bend the hall switch legs
2. glue the hall switch with a spot of superglue
3. (LED option) trim the LED legs
4. bend the K leg of the LED as shown
5. glue the LED in the hole with a spot of superglue
6. trim the wires and pre-solder their ends
7. insert the wires and solder to the hall switch
8. trim and bend the resistor legs as needed
9. solder the resistor(s) to the other parts

At this point the sensor can be tested, just connect +5v and ground to the RED and BLACK wires and when a magnet comes near the LED with light up.


Filling with epoxy

If sensor tests ok, put hot melt glue around the wire to stop epoxy leaking out. You can use modeling clay for this but use a LOT and make it physically supported to the mount AND a base plate so nothing moves until the epoxy sets, this may take 24 hours. I much prefer the hot melt glue. You can also use silicone (silastic) to seal it but this takes longer to set and is harder to remove than hot melt glue.

Fill pocket with epoxy or 5 minute araldite. The 5 minute araldite is much thicker and won't tend to leak as bad, but it will be yellow and less attractive and is typically a low quality material with less sealing ability and worse temperature properties. Other 2-part epoxies will take longer to set, and can leak if not sealed well, but when fully set are superior.

Don't use polyester resin (the stuff you put a few drops of hardener in). This has poor shrinkage properties and will often pull away from the sides of the pocket allowing moisture in or allowing the hall switch to vibrate or move. It can also be corrosive to wiring and components.

[RomanLini]

Originally Posted by Ernie34 Guess what I am doing tomorow! Awesome job!!!!!!

Thanks Ernie!

Please post pics of anything you make, especially changes and improvements.

[Ernie34]

I think you hit the nail on the head man. That is a very simple and easy design. I will be milling this on a drill press, Yea I know it not a very precise way of doing things but it will work. I am ordering the hall effect sensors now! Have you thought of milling it out of aluminum and mixing air into the epoxy, That way the epoxy would give a nice glow. Of course you wouldnt mill the hole for the LED, The epoxy would hold it in.

[RomanLini]

That's a good idea, I'm sure some people would prefer a solid aluminium mount.

You could make the LED shine out the top side of the pocket (like I think you are suggesting) but normally the magnet would be over that side when the LED activates, and the magnet may also be attached to a side plate of the machine etc so in some cases that might not be the best location. That all depends on how you position the sensor and magnet on the machine of course.

If you put the LED in the same location as my diagram you could poke it out the end of the aluminium mount and just seal it, the wires have to be sealed anayway so sealing the LED too is no big deal.

[Ernie34]

Looks like I need to go get some scrap aluminum to play with!

[Jesse B]

Those look great Roman. There's an infinite amount of modifications that could be done to suit people's needs, but this seems to be the perfect base platform to go off of. I'm definitely going to incorporate these into my machine one I get it built.

[Ernie34]

Hall effect sensors are on backorder at Mouser. Trying Digikey now. grrrrr

[Ernie34]

Digikey has them instock. Ordered 10 sensors, 100 resistors and the order came to 16 bucks. Not to shabby. Ill post pics when built.

[eloid]

looks good ,

but I had a thought .... "how is the sensitive" of the hall sensor for distance.

would it not be more ideal to have sensor placed (in the middle of the case but closer to the edge?) rather to the far side... the led can stay in orginal place.... this way the switch could be used in vertical postion or horizontal postion. Thus the switch can be mounted in tigher spaces or use the mount holes more effectivly for ajustment if needed... ie z axis you may not have the physical width on the carrage to place the sensor along the width. ( also this way you dont lose .5 inch of travel due to placement of hall sensor in the case)
I can see how a pcb can make the placement of circuit easyer.... pcb would have a nice press fit for casting pocket and would be snap to center... just dont have the time to draw it up... to many projects on the go right now...

[epineh]

Originally Posted by RomanLini Maybe someone who uses the popular CAD program (I don't even know which CAD program is most popular here!) can whip up a CAD design.

Consider it whipped

The drawing is what I would call the plan elevation, should be enough to make most of the part, you will have to work out the 3mm hole for yourself. I saved it as an AutoCAD 2000 binary DXF, should work with most CAM software, your mileage may vary.

I used ProgeCAD btw, free for private use

Russell.