Which Type of Limit Switch

[irving2008]

Hi Ray,

You need NPN NC switches. I'm fairly sure, but not 100% that your BOB doesn't have opto-isolated inputs (the manual is useless), but maybe someone can confirm this. Do you have a voltmeter/multi-meter? If so measure the voltage from limit switch input to ground (with power on the BOB). If its more than 2v then its probably not opto-isolated and if it 5v it probably has an internal pull up. In which case wire the switch as:
.
Brown: +12 or 24v power supply
Black: To BOB limit input
Blue: to Ground on BOB limit input AND to Ground on 12/24v supply.
.
Now you need to decide for X and Y if home is at one end of table travel or in the middle (Z home is always the top). Since proximity sensors work on approach of ferrous material, if Home is in the middle of the movement range, Mach has the problem of knowing which side to approach the sensor from since approaching from either side will give the same result electrically but will be offset by potentially 8mm mechanically. I don't know how you tell Mach to home from a given direction, but I'm sure it can be done...
.
edit: Eddy types faster lol. But I want to reiterate the proximity sensor accuracy previously discussed is for material approaching axially (i.e. towards the end of the sensor). For this requirement the approach will have to be radially, i.e. across the face.

[EddyCurrent]

edit: Eddy types faster lol.

Sometimes it's best to type it up into Notepad first then just paste it into a post.

[cropwell]

I don't know how you tell Mach to home from a given direction, but I'm sure it can be done...
.

In Mach3 there is a dialogue box to set the homing direction of each axis.

[irving2008]

In Mach3 there is a dialogue box to set the homing direction of each axis.

Right, not used it myself. Presumably you need to set up the nominal home location and Mach3 moves far enough to the appropriate side of that to approach from the right direction.

[Clive S]

Just a thought although all of the above is correct are we assuming that the sensor has a resistor built in of say about 10K If not would it be prudent to put a current limiting R in.. My sensors have 10K internal so not neaded.

Also if you home at the middle you have gcode with -ve and +ve code I find it more convenient to have the home switch at one end then all gcode is +ve (for me being a novice it's easier to read) ..Clive

[cropwell]

Right, not used it myself. Presumably you need to set up the nominal home location and Mach3 moves far enough to the appropriate side of that to approach from the right direction.

All Mach3 does is have a set direction to move an axis when heading for home (the home sensor). After detecting the sensor Mach3 then backs off a little and zeroes the DRL. This, presumably, is not intended for having a home position in the centre of the table. I could give you some screenshots, but my Mach3 computer is disconnected whilst I rebuild the control box. If you had an input set to 0/1 depending on which half of the axis you were in, then I am sure some clever sod could write a macro to centre the axis.
I think you mentioned previously that proximity switches work on detecting ferrous metal, which is true, but mine also work on ali and brass. The ones I use are 4mm axial detection, but I use them in bypass mode, where the detection position is not necessarily 4mm, but it is consistent. In axial mode you have a great danger of jogging onto the switch and crushing the end, which kills it. (That is why I have the spares, bought as a lot of 8 from china.)

To Ray:- You have to regard a proximity switch as an off/on (ie normally open) push button switch, but it needs 6 to 36v to make it work. The ground connection is common to the switch and the electronics in there. 5v won't cause it to switch, either not at all or not reliably.
PM me with your phone number if you want to talk it through. I have got 5 LJ12A3-4-Z/BX switches and some 12v power supplies, which are intended to be used in my next build.

[manofgresley]

Ray

You need NPN NC switches. I'm fairly sure, but not 100% that your BOB doesn't have opto-isolated inputs (the manual is useless), but maybe someone can confirm this. Do you have a voltmeter/multi-meter? If so measure the voltage from limit switch input to ground (with power on the BOB). If its more than 2v then its probably not opto-isolated and if it 5v it probably has an internal pull up. In which case wire the switch as:
.
Brown: +12 or 24v power supply
Black: To BOB limit input
Blue: to Ground on BOB limit input AND to Ground on 12/24v supply.
.
Now you need to decide for X and Y if home is at one end of table travel or in the middle (Z home is always the top). Since proximity sensors work on approach of ferrous material, if Home is in the middle of the movement range, Mach has the problem of knowing which side to approach the sensor from since approaching from either side will give the same result electrically but will be offset by potentially 8mm mechanically. I don't know how you tell Mach to home from a given direction, but I'm sure it can be done...
.
edit: Eddy types faster lol. But I want to reiterate the proximity sensor accuracy previously discussed is for material approaching axially (i.e. towards the end of the sensor). For this requirement the approach will have to be radially, i.e. across the face

[manofgresley]

Hi Irving, i have stated already, my BoB is only 5 volts, are you now saying i can wire a 3 wire sensor direct on to the Bob?

Ray

Ray

You need NPN NC switches. I'm fairly sure, but not 100% that your BOB doesn't have opto-isolated inputs (the manual is useless), but maybe someone can confirm this. Do you have a voltmeter/multi-meter? If so measure the voltage from limit switch input to ground (with power on the BOB). If its more than 2v then its probably not opto-isolated and if it 5v it probably has an internal pull up. In which case wire the switch as:
.
Brown: +12 or 24v power supply
Black: To BOB limit input
Blue: to Ground on BOB limit input AND to Ground on 12/24v supply.
.
Now you need to decide for X and Y if home is at one end of table travel or in the middle (Z home is always the top). Since proximity sensors work on approach of ferrous material, if Home is in the middle of the movement range, Mach has the problem of knowing which side to approach the sensor from since approaching from either side will give the same result electrically but will be offset by potentially 8mm mechanically. I don't know how you tell Mach to home from a given direction, but I'm sure it can be done...
.
edit: Eddy types faster lol. But I want to reiterate the proximity sensor accuracy previously discussed is for material approaching axially (i.e. towards the end of the sensor). For this requirement the approach will have to be radially, i.e. across the face