Limit switches & auto tool height setter?

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

Post by Jim » Fri Jan 23, 2015 7:59 pm

Great thanks. Now, I need to translate this to my TinyG... GND is obvious to me, A5 is the pin (Zmin, in my case), correct? And IOREF is my 3.3V pin???

Thanks for your help on this.
Jim

Shapeoko 2 #7699 w/TinyG controller

Jim
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Joined: Wed Oct 29, 2014 10:15 pm

Re: Limit switches & auto tool height setter?

Post by Jim » Fri Jan 23, 2015 8:23 pm

OK, I am now studying the schematic more for the touch plate and I am confused as to what R2 is doing for me. In my simple mind it appears to be completing the circuit between IOREF (assuming that is my 3.3V) and the A5 pin.

If you tell me, "it just works"... I will believe you, but I just see a completed circuit. The diagram for the switches make sense to me though, and that's what I figured, albiet I have separate xMin/xMax pins so I will not do them in parallel (that also goes for the y, z, and a axes).

Finally (hopefully) since my output voltage is 3.3v and not 5v will I need different values for R1, R2, and/or C1?

Thank you
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 8:41 pm

Oops, yes, sorry, for the TinyG the pins are named differently. Instead of IOREF use whatever the I/O voltage is, I believe 3.3 V; and A5 is the probe input pin, presumably Zmin.

If you have separate min and max limit switch inputs, then you don't need the other circuit -- but I thought you asked about it, because that's what I was talking about in that post. Note that if you have Z limit switches, you can't wire the Zmin limit switch like that and still use the touchplate. It has to be normally open and connected only to GND.

The same values for the parts will work fine at 3.3 V too; they're not critical.
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Jim
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Re: Limit switches & auto tool height setter?

Post by Jim » Fri Jan 23, 2015 8:51 pm

I was asking about the switches because I will be using those for everything other than zMin. For zMin I will use the touch plate. But then you said.
cvoinescu wrote:Note that if you have Z limit switches, you can't wire the Zmin limit switch like that and still use the touchplate. It has to be normally open and connected only to GND.
Are you referring to the first schematic or the second one? If you are referring to the second schematic (switches), that makes since as I will not gang my min and max switches together anyway, but make them all separate.

Are you tying the signal pin to ground to help reduce noise?
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 9:18 pm

What I mean is that you can't have a changeover switch, connected to both VDD and GND, and still use the touchplate on the same input pin. If you don't have a Zmin switch, just the touchplate, then you're fine.

The switches, as drawn, appear normally closed to the controller. To make them appear normally open, connect NC to VDD, NO to GND, and C to the respective input pin. NC and changeover switches are less sensitive to false triggering than NO switches, because, in their normal state (limit not reached), a switch contact is closed and the input is connected to a set voltage. Some types of noise have more trouble affecting a low-impedance circuit like that.
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Jim
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Re: Limit switches & auto tool height setter?

Post by Jim » Fri Jan 23, 2015 9:30 pm

Yes, I have a separate zMin and zMax, so I would have the changeover switch for my zMax limit, but only a touch plate for zMin (no switch).

Unfortunately, TinyG does not (yet) let us mix and match NO and NC switches-it's one or the other. So I will have to make all switches NO.
Jim

Shapeoko 2 #7699 w/TinyG controller

Jim
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Re: Limit switches & auto tool height setter?

Post by Jim » Fri Jan 23, 2015 9:59 pm

Now I am looking at the TinyG Schematic and I noticed that it appears that the pins are already going though capacitors and resistors--would that change anything in regards to the touch plate design?
Partial TinyG Schematic.PNG
Partial TinyG Schematic
Partial TinyG Schematic.PNG (54.67 KiB) Viewed 1852 times
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 10:14 pm

Given what they have there, you may be better off connecting the touch plate directly, no resistors and capacitors. If you find you get false triggers and decide to try that schematic, reduce R2 to something like 100 ohms, and use a larger capacitor (1 uF).
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khauser24
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Re: Limit switches & auto tool height setter?

Post by khauser24 » Sun Jan 25, 2015 3:25 am

If it helps you can use a simple transistor to make a NC out of a NO. Here's a sample circuit: http://www.instructables.com/id/Make-a- ... ds-sort-o/

Jim
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Re: Limit switches & auto tool height setter?

Post by Jim » Sun Jan 25, 2015 3:44 am

khauser24 wrote:If it helps you can use a simple transistor to make a NC out of a NO. Here's a sample circuit: http://www.instructables.com/id/Make-a- ... ds-sort-o/
That's very interesting. But, not being an electronics engineer, I wouldn't know what kind, size, etc. of transistor to use.

Thanks anyway and I will keep this filed away if some revelation comes about.
Jim

Shapeoko 2 #7699 w/TinyG controller

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