Wiring Limit, Home and E-Stop Switches

[TarHeelTom]

Tom,

I don't have a BOB but my driver board does have a terminal for the unused parallel port pins. Separate from the parallel port, it also has one terminal for each set of axis limit switches. I was not intending to use those, since I wouldn't be able to jog off of the limit switches. I was wondering, though, if I could wire the E-Stop to those. Either that or just switch the incoming power.

I guess my question is if it is preferable to have both the software and hardware stop when the E-Stop is hit or if stopping just the hardware is sufficient.

Don't know why you can't jog off the limit switches. If you use only one pin for all of the limit switches, for instance, three NC limit switches in series, to break continuity to the pin, but with a separate push button to override the limit switch as you jog back.

It would be nice (is it possible?) to use an input pin to tell the software that the eStop has been triggered. Certainly it's possible to send the eStop signal to the pin. Have no idea if either Mach3 or EMC2 will recognize that software. That quote seems to indicate that Mach3 will recognize the eStop input.

Remember that even if you tell the software that you've hit eStop, the software has no way of knowing where the steppers are NOW, as they coasted to a stop. Which means you've got to rezero all the axes.

Basically speaking (and I've not ever used Mach3) you have a configuration table which you use to tell Mach3 or EMC2 what function each pin has, and whether it's a positive or negative input.

Although the capacitors can keep running the motors for a while if you switch the AC to the power supply, cutting the DC supply FROM the power supply would result in nearly an instant stopping of the motors, after the normal slowdown time.

Tom

[gpraceman]

Don't know why you can't jog off the limit switches. If you use only one pin for all of the limit switches, for instance, three NC limit switches in series, to break continuity to the pin, but with a separate push button to override the limit switch as you jog back.

The driver board manual does say that you have to move off the switch to re-enable the axis, if using the board's limit switch inputs.

It would be nice (is it possible?) to use an input pin to tell the software that the eStop has been triggered. Certainly it's possible to send the eStop signal to the pin. Have no idea if either Mach3 or EMC2 will recognize that software. That quote seems to indicate that Mach3 will recognize the eStop input.

Seems quite possible. I just am not sure how to wire things up to let both the driver board and the software know that an E-Stop has been hit. The driver board operates off of a higher voltage that the parallel port, so it doesn't seem straight forward.

Remember that even if you tell the software that you've hit eStop, the software has no way of knowing where the steppers are NOW, as they coasted to a stop. Which means you've got to rezero all the axes.

That seems to be a given as the Mach3 manual also states

It will not generally be possible to continue machining a part after an EStop but you and the machine will at least be safe.

[TarHeelTom]

Seems quite possible. I just am not sure how to wire things up to let both the driver board and the software know that an E-Stop has been hit. The driver board operates off of a higher voltage that the parallel port, so it doesn't seem straight forward.

You've got 24V available. One easy way is to use the contacts on a very small 24V relay to tell the pin that things are normal. You power the coil routinely with the 24V line to the driver board. Use the NC eStop switch to interrupt the 24V to the driver board and the relay coil, which either opens or closes the relay contacts to send your message to the input pin to the computer.

Actually, you could use either a relay with multiple contacts, or multiple relays to send the same signal to other receptors, as needed. One might be spindle power. In my case, I'll use some contacts, relay or switch, to break the common return line from the run contacts on the VFD. VFD's don't like to have any contacts between the VFD and the motor.

Another simple method to send the message to the pin would be an opto-isolator. These are very simple chips, and are readily available. My BOB has an opto-isolator on the board for every pin, except for the pins feeding the geckos, which have their own built-in opto-isolators.

As an aside, this is a benefit of buying a slighly more expensive BOB, as it has more features, such as relays and opto-isolators already installed on the board, making the installation of lines for other purposes so much easier and simpler.

[gpraceman]

As an aside, this is a benefit of buying a slighly more expensive BOB, as it has more features, such as relays and opto-isolators already installed on the board, making the installation of lines for other purposes so much easier and simpler.

Actually, the driver board that I have does use opto-isolators for the parallel port interface.

All inputs signals are optocoupled for PC parallel port protection

They do offer a twin relay board that I was considering getting for use in turning the spindle on/off. They have instructions on how to easily wire it to the driver board. That would leave a free relay.

[TarHeelTom]

Actually, the driver board that I have does use opto-isolators for the parallel port interface.

They do offer a twin relay board that I was considering getting for use in turning the spindle on/off. They have instructions on how to easily wire it to the driver board. That would leave a free relay.

Good plan.


Tom

[gpraceman]

I've been thinking about it a bit more. The E-Stop button has a set of NC and NO contacts and there is no common ground (at least it appears that way). So, wire the NC terminals to pin 15 of the parallel port to let Mach3 know of the stop and use the NO contacts to the limit switch terminals on the driver board. Looking at their datasheet, they show the limit switches wired up as NO.

I went ahead and ordered the E-Stop switch. Once I get it in hand, I'll see if the ground terminals are common or not.

[Crevice Reamer]

There ARE DPST NC Estop switches, but they are quite expensive. I wanted such a switch for my G0602 project, but didn't want to pay the requisite arm & leg.

Most of the switches we buy (I'm using the one from Keling) are made in two separate parts. (well actually three) A mechanical half and an electrical half. The electrical half consists of 2 removable modules that contain everying including the actuator plunger.

The modules just snap into place and CAN be interchanged. I'm sure that you could buy a NC module somewhere, but I suspect you would have to buy 10,000 or so.

http://i733.photobucket.com/albums/w...786_edited.jpg

My solution was to buy TWO of the cheap Keling switches and interchange the parts to make one douple pole Normally Closed switch:

http://i733.photobucket.com/albums/w...792_edited.jpg

As you can see, neither the grounds, nor anything else are common.

CR.

[gpraceman]

That looks just like the switch that I ordered. From your photo, it does definitely look like the NO and NC sides are electrically isolated from each other.

For my driver board, it looks like the limit switches need to be NO. Closing a switch will kill that axis. With the NC and NO sides of the switch being independent, I can use the NC side wired to the parallel port pin 15 and NO side to the limit switch terminals for all 3 axis on my driver board.

[Crevice Reamer]

That looks just like the switch that I ordered. From your photo, it does definitely look like the NO and NC sides are electrically isolated from each other.

For my driver board, it looks like the limit switches need to be NO. Closing a switch will kill that axis. With the NC and NO sides of the switch being independent, I can use the NC side wired to the parallel port pin 15 and NO side to the limit switch terminals for all 3 axis on my driver board.

It's generally considered a bad idea to wire limit switches NO. If a wire breaks or comes loose, the limit will be inop but you won't know it until after the crash. Whereas if wired NC nothing works until the broken wire is fixed.

CR.

[gpraceman]

It's generally considered a bad idea to wire limit switches NO. If a wire breaks or comes loose, the limit will be inop but you won't know it until after the crash. Whereas if wired NC nothing works until the broken wire is fixed.

Yes, so I have gathered that from discussions on this forum. I'm just reading the wiring diagram for my driver board.

http://www.easy-cnc.com/web/download...s%28NEW%29.pdf

I'll actually be wiring some NC home and limit switches directly to the parallel port. The driver board does not have a terminal for an E-stop switch, so I thought that I could take advantage of the onboard limit switch terminals.

[15mgtar]

Guys how do you connect 2 home switches for Y axis with 2 motors on it?

[Crevice Reamer]

Guys how do you connect 2 home switches for Y axis with 2 motors on it?

You only need one switch.

I guess you would like to detect axis racking, but it won't work. Mach3 will stop when only one switch is thrown. Even if you had two switches synched up and wired in series, If one switch was racked out of place, Mach3 would still accept the first switch that closed to be the true home position.

CR.