Touch probe to ir receiver??

[REVCAM_Bob]

O.K. for the electronic gurus.... Here are a couple links to some simple ir reciever units i.e. one you can buy for $15....

Could these be used to receive a signal from an electronic edge finder i.e.
the kind with the red light emmiting diodes on them? And if so, are there
any cheap probes out there that this could be used with also?


http://www.factorydirect.co.uk/facto...rreceiver.html

http://lnx.manoweb.com/lirc/

[Meganick]

Need to consider a few things.

-TV remotes modulate the LED source at frequencies from 38-60kHz to form pulse streams. See http://www.everlight.com/pdf/Irm-8601s.pdf . So it is a little more complicated than a simple on/off touch/no-touch indicator

-An example of the actual pulse stream that the a remote sends out is shown half way down this page http://lnx.manoweb.com/lirc/?partTyp...&partName=lirc . Note that the time scale is 5msec/unit and that some of the commands take almost 30 units or between 100-200msec. This is not a fast protocol. You probably would not want to use this for a CNC edgefinder unless you were going VERY VERY slow.

-Also need to come up with a way to tell a CNC program that you Are Touching, Not Touching, or Not Sure incase the IR connection is interrupted.

[REVCAM_Bob]

Can't it sense just on and off?

[REVCAM_Bob]

I think I can tell cnc to stop o.k., and already have the ability to read the
machine postiion..... Just need the signal...

[Meganick]

Some exampes of transmitters can be found here in the Home Brew section: http://www.lirc.org/

What you'd be looking at could be a small PIC or other microcontroller that would be built into the edge finder that would modulate the LED to generate two different button push pulse sequences depending on whether or not it is touching.

So again the real question is can you tolerate a delay of say 1/4 second from the time contact is made to when the controller is actually signaled that you have contact? During that time, the motor will continue to advance the table. Say you had were advancing at 4mil/sec to an edge, you would overrun by 1mil in the 1/4 second.

What are typical edge find approach rate numbers?

Maybe a better way would be to have the edge finder put out a button sequence that is interpreted by CNC controller as a jog/advance signal. So form the time you say go, each pulse output is used to advance the controller one jog step until you touch. If the IR gets interrupted, it stops.

This is sounding interesting. Tie the IR receiver into a ModBus module/Mach3

[Meganick]

And if you designed your own custom decoder, you could should much shorter code sequences.

[REVCAM_Bob]

I guess maybe I am overcomplicating this.

My bad, not really thinking infrared, just red led, or are they one in the same?

Isn't there a simple way just to detect if and led on a simple electronic
edge finder is on or off?

[REVCAM_Bob]

Meganick, I really do not even know what approach speeds would be...

Maybe some of you guys that have used probes could clue us in?

I would imagine a sequence could be used to do a rough approach at a higher
speed, then a slow approach to minimize overshoot....

[Meganick]

You can hack into it and just run out an extra wire...

Even better would be a pair of wires coming off the edge finder run thru an optoisolator.

[REVCAM_Bob]

Trying to do wireless, so edge finder can be stored in turret for unattended
operation...

[chuckels]

If I understand you I think what your after is a photo transistor which is basically a light operated switch to turn on and off when the LED turns on and off right?
the electronics gurus should be able to draw a quick circuit to interface with your inputs.
chuck

[REVCAM_Bob]

Chuckles, yes that is it! Something simple, but could the ir receivers i.e. these things already built that plug into a serial port do it also?

Of coarse if a photo transistor could do it, then I could tie directly into
the input of a galil card or ethernet i/o unit which could be easier.....

Could a photo transistor pick up a red led on an electronic edge finder from
the corner of a machining center??