Which Type of Limit Switch

[Clive S]

Hi Eddy. I'm confused, why do i need a separate 5 volt psu, when my BoB is already putting out 5 volt. On the board there are terminals for 5 limits but only two wire each, + & -, Am i reading it wrong or what?

Ray

I don't know your BOB but you have to power it from somewhere I and others are assuming it is powered from a 5V source if it is powered from 12V then you can use that to drive your sensors.
Can you confirm what the BOB is powered from? ..Clive

[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.

[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