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Odd behavior with probe wiring
« on: May 03, 2014, 04:14:31 PM »
I have decided to use a z probe for setting the tool height. I connected the board to a spare terminal on the c10 breakout board and configured the probe input in Mach 3.  When I touch the copper plate with the alligator clip, Mach 3 shows a good contact. It works as it should.  However, if I use the tool on the router, nothing happens.  If I pull out the tool, the input lights up. That is, when the tool makes contact with the router , the probe no longer works.
Somehow, the router is interfering with the circuit, and I can't figure out why.
After all, I am only using the tool for closing the circuit.
The router is a hitachi plugged in its own 110volts line Clearly, the router is interfering with the circuit.

Any clues?
tony

Offline mbele

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Re: Odd behavior with probe wiring
« Reply #1 on: May 04, 2014, 06:31:01 AM »
Here's how it works for me (I think I have c10, too):
- my router is grounded (it seems that yours is too), so I do not have to ground the tool with aligator clip wired to breakout board ground
- PCB is connected to breakout board input
- the same input is connected to +5V (right next to input) via resistor (2k2 1/4W i think), so that normaly, open circuit is "high" signal state
- when tool touches PCB, it grounds probe input (brings it "low")
- mach is configured so that open circuit is "high", and closed "low" (Active low)
HTH
Mihael
Re: Odd behavior with probe wiring
« Reply #2 on: May 04, 2014, 08:36:23 AM »
When I wire the pins as described, I get a lot of noise. I am using INput pin 13 for the probe. tony

Offline mbele

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Re: Odd behavior with probe wiring
« Reply #3 on: May 04, 2014, 08:51:06 AM »
I find that odd, I only had problems with noise with grounded PCB, +5V on tool and active-high circuit logic. Have you tried connecting capacitor (ceramic 0.1uF) between input and ground ?
Re: Odd behavior with probe wiring
« Reply #4 on: May 04, 2014, 09:26:25 AM »
Here's the great puzzle:
The probe connected on one input line works properly. The lights come on normally when I short the alligator clip and the copper plate.
If I do this when the tool is inserted in the router, I see a major current draw in the system( the monitor actually flickers and the breakboard led dims). This tells me that the router is creating a separate ground in the system.
I have the router completely isolated from the cnc frame by using a pvc sleeve in the router mount.  However, the multimeter indicates a resistance of 10k between the router frame and the router body when I have the router plug connected in the outlet, and a resistance of 1k when I pull the plug out.
So my question and puzzle is ..... how is this router making contact with the frame, and if so how do I proceed?
How is the router interfering with the probe circuit?
tony

Offline stirling

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Re: Odd behavior with probe wiring
« Reply #5 on: May 04, 2014, 10:00:52 AM »
It's a little confusing from your post exactly how you've wired what to what. For example in your post above you mention probe, plate, tool and clip.
You appear to have your PLATE connected to an input but what is connected to your CLIP.
Also please post the xml file you're using.
Re: Odd behavior with probe wiring
« Reply #6 on: May 04, 2014, 10:25:56 AM »
There are two input connections on the breakout board: a numbered input and a +5volt next to it.  As described in several sites, the "alligator" is connected to the NUmbered input, in my case, #13. The plate is connected to the adjacent 5 volt line.  This is how I have wired my three homing switches, and they've been working well for years.
My assumption, therefore, is that I am simply creating a circuit that "shorts" these two lines.
Again, when I do this without making contact with the router, it behaves as it should.
I have also tried placing a 10k resistor between the numbered line and the 5volt, but it , too, does not work.



tony

Offline stirling

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Re: Odd behavior with probe wiring
« Reply #7 on: May 04, 2014, 10:59:35 AM »
OK I remember seeing another post like this a while back. (http://www.machsupport.com/forum/index.php/topic,26294.0.html)

I don't know why people wire them like this - it's a really crap way to do it and MORE than likely to result in the effects you're seeing. Particularly the short which is VERY likely to damage something if it hasn't already.

You'd be FAR better off wiring the plate to your input pin and setting that input pin in Mach to active LOW. Then connect your clip to GROUND and clip it onto your tool. FORGET the 5V supply terminal - you're asking for trouble.

Now the plate will be sitting at the pull-up of the input and connecting it to ground with your clip/tool will signal an active low to Mach. No danger of shorts or anything else. The worst that can happen is you put the plate on a grounded surface and then it'll signal Mach - but that's all - it won't short anything out.
Re: Odd behavior with probe wiring
« Reply #8 on: May 04, 2014, 11:03:24 AM »
I'll give that a try and report back. thanks
tony
Re: Odd behavior with probe wiring
« Reply #9 on: May 04, 2014, 11:12:55 AM »
When the plate is connected to the input line, and the alligator is connected to the "power ground" on the breakout board, the circuit simply does not work, regardless of how I set Mach 3 input states.
tony