Limit switches & auto tool height setter?

Discussion of tinyG control platform
dataway
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Re: Limit switches & auto tool height setter?

Post by dataway » Fri Sep 05, 2014 5:47 pm

@chmedly
you are correct i have my alligator clips wired to the z-min and ground with a 1K resistor in series with the plate and z-input and the other is wired to ground directly. I have had no issues with static and I live in the local Mountains where the air is dry and static is prevalent....
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chmedly
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Re: Limit switches & auto tool height setter?

Post by chmedly » Sat Sep 06, 2014 12:05 am

cvoinescu wrote:330 Ω pull-up (between plate and VDD), 1 kΩ in series (between plate and pin), and 1 nF to ground (between input pin and GND) should take care of that.
You wouldn't do a zener or two?

I need to look at the schematic for the tinyG. I'm curious what kind of buffering is designed into it.

Also, I'm curious about reaction time for the touch off and how likely it is to blunt a tip. Take it slow and use aluminum makes sense.

pastprimitive
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Re: Limit switches & auto tool height setter?

Post by pastprimitive » Sat Sep 06, 2014 4:17 pm

on my touch probe I backed it with a bit of 2mm adhesive craft foam on a pcb. So it has a little spring to prevent blunting.
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dataway
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Re: Limit switches & auto tool height setter?

Post by dataway » Mon Sep 08, 2014 7:11 pm

I have not had a problem with it blunting my bit but I did slow down the seek speed of the z-axis ..
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chris33
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Re: Limit switches & auto tool height setter?

Post by chris33 » Mon Sep 08, 2014 8:42 pm

Could i use a fsr as a toouch probe ie put it as a lower limit switch so the tool tip will home in onto the fsr to 0 the z height the offset would be the thickness of the fsr
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jkanzaki
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Re: Limit switches & auto tool height setter?

Post by jkanzaki » Thu Sep 25, 2014 5:17 am

cvoinescu wrote:330 Ω pull-up (between plate and VDD), 1 kΩ in series (between plate and pin), and 1 nF to ground (between input pin and GND) should take care of that.
Hi Cvoinescu or dataway
Would you mind draw a simple circuit diagram on how to acutally hook up the prob / resistor?
I know how to solder and all that but I can't quite figure exactly the set up here for the prob.

thank you very much
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Jim
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Re: Limit switches & auto tool height setter?

Post by Jim » Fri Jan 23, 2015 3:45 pm

cvoinescu wrote:330 Ω pull-up (between plate and VDD), 1 kΩ in series (between plate and pin), and 1 nF to ground (between input pin and GND) should take care of that.
Yeah, I am wondering about wiring this up too. First, I am assuming that "plate" refers to the touch plate on the work piece and "pin" refers to the mill end. If my assumptions are wrong, then that is part of my misunderstanding...

Based upon my assumptions, I get the "330 Ω pull-up (between plate and VDD)" and I get the "1 nF to ground (between input pin and GND)", but I don't get how I can wire up a "1 kΩ in series (between plate and pin)" with out completing the circuit (triggering the homing switch) and/or changing the the height of the plate.

Any insight on this would be great.
Jim

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cvoinescu
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Re: Limit switches & auto tool height setter?

Post by cvoinescu » Fri Jan 23, 2015 4:23 pm

"Pin" is Arduino pin used as the probe input (A5, IIRC). The endmill is simply connected to GND with an alligator clip. "Plate" is indeed the touch plate. Does it make sense now? If not, I'll draw the schematic.
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Jim
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Re: Limit switches & auto tool height setter?

Post by Jim » Fri Jan 23, 2015 4:38 pm

cvoinescu wrote:"Pin" is Arduino pin used as the probe input (A5, IIRC). The endmill is simply connected to GND with an alligator clip. "Plate" is indeed the touch plate. Does it make sense now? If not, I'll draw the schematic.
I found one of your other posts related to limit switches and it is starting to become clearer, but yes, I think a schematic will be helpful. I have a TinyG and not a Grbl, but I am guessing the principal will be the same.

In your other posting, Normally Closed Limit Switches 2, you are talking about wiring up switches (not a touch probe) and I think I am starting to grasp what you are saying with wiring the three wires up. In that case you are wiring up the pin (COM on the switch) to ground (NC on the switch) I assume to minimize noise?, then wiring VDD to (NO on the switch) so that when the switch is triggered, it will send the voltage to the pin, triggering the limit. (Am i getting close?)

Since noise on normally open circuits seems to be a problem, I was thinking about getting wire with a shielded jacket (Mylar foil) and a drain wire. Would it be appropriate to wire the drain wire to ground, or do I need to find a three conductor cable?

Thanks and I look forward to a schematic on how to wire up the touch plate.
Jim

Shapeoko 2 #7699 w/TinyG controller

cvoinescu
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Re: Limit switches & auto tool height setter?

Post by cvoinescu » Fri Jan 23, 2015 7:30 pm

Here's how I'd wire the touchplate:
touchplate filter circuit.png
touchplate filter circuit.png (7.93 KiB) Viewed 2285 times
I'd recommend R1 = 330 Ω, R2 = 2.2 kΩ, C = 100 nF (I've changed my mind since I posted what you quoted).

And here's what I described in words in the other post:
changeover limit switch wiring.png
changeover limit switch wiring.png (5.43 KiB) Viewed 2285 times
You can use the same filter circuit for the limit switches too, for better noise protection. For NC limit switches, I'd use R1 = 1 KΩ.

IOREF is the correct voltage for the inputs of the Arduino, regardless of type (so it's +5 V for the Uno and Mega, but +3.3 V for the Due and the upcoming Zero). It's good practice to use that rather than +5 V or +3.3 V, if the circuit permits.
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