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Offline kolias

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Touch Probe Problem
« on: January 09, 2014, 01:44:30 PM »
My zero touch probe consists of an alligator clip to attach to the spindle and a 1/8" aluminum plate for the bit to touch and set the probe.

I used the "automated setup of inputs" to set my inputs and the probe is assigned to pin 11, E-stop to pin 10. When I touch the alligator clip to the spindle the E-stop is activated. When I touch the 1/8" plate to the spindle nothing happens. When I touch the alligator clip to the 1/8" plate nothing happens.

Between the alligator clip / plate and my control panel I have a DB9 connector to easily connect the probe when it is needed and checking the pins on the DB9 I have +5V. I also tried to change the Active Low / High but the result is the same.

Any idea why this happens?
Nicolas

Offline Hood

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Re: Touch Probe Problem
« Reply #1 on: January 09, 2014, 04:41:14 PM »
Sounds like either you are getting noise on the input or you have it connected to Pin 10.
Hood

Offline kolias

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Re: Touch Probe Problem
« Reply #2 on: January 09, 2014, 05:59:09 PM »
I was checking the wiring and did not see anything wrong but I will check again. I was also checking my limits with the axis moving now and found out that only the X axis when she hits either limit (left / right) I cant back out and the only way I can do that is go to the inputs screen and change the active low / high tick manually. On the Y & Z axes limits works ok and I can back out fine

Also on the X axis when I try to reset and this message comes on which says to fix the problem, it can't fix the problem, and I have to change as I said the active low / high tick manually. The e-stop and all limits have the active low / high tick in green and they work fine except the X axis

Thanks Hood
Nicolas

Offline kolias

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Re: Touch Probe Problem
« Reply #3 on: January 17, 2014, 11:57:57 AM »
With the help from another source I finally got my zero touch probe working and for the benefit of other forum members this is how it was done.

The C10 input pins have a dip switch which sets the pins to pull down or pull up. I have set this dip switch to pull down and all limits / home switches are working well except the probe. So I was told to install a current limiting resistor as per attached schematic and now the probe is working just fine.

Since I did not have a 1K resistor, I have installed a 36 ohms, 10W one which I had and the probe still works fine. I plan to get a 1K when available in my local store
Nicolas
Re: Touch Probe Problem
« Reply #4 on: January 17, 2014, 02:07:30 PM »
A 1K resistor limits the load on the input to 5 milliamps. Your 36 ohm resistor puts a 138 milliamp load on the input and could potentially damage it, depending on how the circuit is built. Get the right one, right away!

Offline kolias

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Re: Touch Probe Problem
« Reply #5 on: January 17, 2014, 03:29:25 PM »
Although the probe is very useful, I hardly use it and when I use it it only touches the plate for a second and then my depth is set for the day. But I will get the 1K resistor as soon as it comes to the store
Nicolas

Offline stirling

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Re: Touch Probe Problem
« Reply #6 on: January 18, 2014, 06:17:29 AM »
That resistor is a complete red-herring and is doing NOTHING except taking your nominal 5V (logic 1) down to around 4.8V (still logic 1) when you touch the clip to the plate. EDIT: but see my edit below.

It is doing this because together with the pull down resistor you've selected with your dip switch it's creating a potential divider on your input when you touch your clip to your plate. Incidentally - if you did as advised and changed it to 1K it would make things even worse and drop your input voltage to around 2.5V which is neither logic 1 nor logic 0. (this is because your pull-down will be around 1K also)

In the absence of more detail I suspect the reason it's now working is simply because you've changed from pull-up to pull-down.

If you had it wired before exactly as you have it now EXCEPT you had pull UP selected then I'm not surprised it didn't work.

With pull UP selected, the pullup was holding the input at 5V (logic 1) and then when you touched the clip to the plate it TOO was applying 5V (logic 1 again) to the input. i.e. you were effectively taking a logic 1 to logic 1 - result zippo change.

Without changing anything else, remove the resistor - it is completely pointless - it's also completely mis-labeled - it's neither current limiting (well not in any way that's remotely useful) nor is it pulling anything up.

EDIT: I just re-read your first post again. If you have 5V on your clip and you're attaching this to the spindle you're asking for trouble. You're VERY likely to short your 5V supply. In this case your 1K resistor would prevent that short (and your 33 ohm mitigate it) - BUT everything I've said above still stands. This is NOT the way to do this. I suggest you stop for a moment and describe your system again otherwise I think you're going to have problems sooner rather than later.

FWIW I think this is why your E-Stop was triggering earlier - you were shorting your logic supply and thus taking EVERYTHING down to 0V.
« Last Edit: January 18, 2014, 07:05:03 AM by stirling »

Offline kolias

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Re: Touch Probe Problem
« Reply #7 on: January 18, 2014, 10:50:41 AM »
Thank you Stirling for your help

My knowledge in electronics is very basic and when I have problems with electronics I relay on forums to get some help if I realize that the vendor I bought my electronics from knows less than I do. The attached link is from cnc4pc but I bought all my drives package from Keling. Page 4 Fig 3 and page 9 Fig 8 are related to the touch probe.

http://cnc4pc.com/Tech_Docs/C10R10_USER_MANUAL.pdf


I know the person who helped me solve the probe problem form last year and as far as I can tell he is very knowledgeable in electronics and provides excellent schematics to help me understand what I should do. If I understand correctly what you are saying in your post is what I have done now to the probe is not a good solution. Perhaps you can direct me on what is a good solution?





Nicolas
Re: Touch Probe Problem
« Reply #8 on: January 18, 2014, 04:36:39 PM »
If the inputs are with pull-down resistors, then the schematic is correct.

Normally input is pulled down to 0V by the on-board resistor. Input state is 0.
When +5V is connected to input, input goes to 5V, and changes state to 1.

The 1k resistor is there to limit current if the alligator clip is accidentally
connected directly to ground. The input has normally enough Rin (input
resistance in this case) to limit current to reasonable value. The circuit would
work even without the 1k resistor (current limited by input Rin), but it is a
good idea to have it there for safety.

The 1k resistor must be sufficiently smaller than pull-down resistor (input voltage
is voltage from divider of pull-down resistor and 1k resistor), which it appears to be.
Often pull-down resistors are 4k7 or 10k.

Offline kolias

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Re: Touch Probe Problem
« Reply #9 on: January 18, 2014, 06:07:06 PM »
Yes I have set the DIP switch to pull-down for all my input pins (setting is either pull down or pull up for all inputs). I understand now that what i did is ok. But i would like to hear Stirling's opinion on this subject too
Nicolas