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Offline olf20

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Auto Tool Zero
« on: November 30, 2008, 12:11:34 PM »
Hi all, hope everyone is doing well!!
I know this has been covered before, but I'm still struggling.
I have everything in place except the wiring on the C1 / C10 bob.
Arturo @ cnc4pc says
 "You need a pull up resistor connected between 5V and pin13.  I suggest a 220ohm (approx).  With this configuration it is required a solid low (GND) in order to get a low in that pin."
Can someone who is using one of  these boards post a drawing of their wiring, or give a detailed
explanation of their setup???
The way I have it is;
5V to 220 ohm resistor
220 ohm resistor to pin 13 - confirmed 5V on pin 13
pin 13 to copper plate
Probe activated as pin 13 active low, port 1
Ground from 5V supply to machine

Thanks for any help!!
olf20

« Last Edit: November 30, 2008, 12:13:21 PM by olf20 »
Mach3, Atlas Knee Mill, 4th Axis, VcarvePro, ESS, Super PID.
Been Heating with corn since 1998

Offline jimpinder

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Re: Auto Tool Zero
« Reply #1 on: December 03, 2008, 11:09:49 PM »
I take it what we are talking about here is the probe facility.

In the computer, whatever pin is allocated to your probe is normally kept high (5v) by the internal resistors in the computer. On the CNC4PC Bob board Arturo has seen fit to reverse these - so by the time you see the pin at the Bob, it is showing 0v.

Check that and see if I am correct - I think I am but I am not sure.

If you are using a copper clad pad, or similar as your touch plate (connected as you seem to say to pin 13) then what you need to do is put a +5v signal to it - not ground (0v) - why mess about with resistors.

Just try this with the diagnostics page on, and, if you touch your pad with a 5 volt lead, you should see the Digitise LED light up.
If it does, then all is working.If it is on then goes off, reverse the "Active Low"

You now have a dilema.
I personally would make an insulated probe of a fixed length that I can put in my chuck, with a +5v lead to it and use it that way.

However, what Arturo is saying is that you need to bring the plate up from it's 0v base to +5v (i.e. it is "on" all the time) then reverse the settings on Ports and Pins to active high - so the computer thinks it is off (because the computer sees it as low) . To do this he is suggesting putting the 5v to the plate through a 220ohm resistor. What would happen then is the tool comes down (and we must assume the tool is at 0v), touches the plate, pulls the plate down to 0v and gives a signal to the computer like that. It is one of the drawbacks of the CNC4PC board.

What I would do (which is even simpler) - and which I have done on mine - is take a lead from pin 13 BEFORE is goes into the Bob electronics, if you can get to it. Take this to a small socket on your electronics box.(a mini jack plug will do). Make up your plate with a wire and plug to fit the socket, so that when you want to use it, you can plug it into the socket  and put it in position on your machine. Bring the tool down (which is normally at 0v - although check there is a return path) touch the plate. This will register, then you can move the tool up and unplug the plate.

Using the socket ensures there are no loose wires floating around when not in use.

 Hope this helps.

Jim Pinder







Not me driving the engine - I'm better looking.

Offline jimpinder

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Re: Auto Tool Zero
« Reply #2 on: December 03, 2008, 11:16:55 PM »
Your little scenario was OK up to a point - but the computer would see a high signal  (the Bob reverses the signals) and would need to be active high.

I DO NOT understand the Ground from 5v supply to machine. If you are meanig a lead from the Bob 0v to your machine, then yes.
Not me driving the engine - I'm better looking.

Offline Greolt

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Re: Auto Tool Zero
« Reply #3 on: December 03, 2008, 11:34:14 PM »

The way I have it is;
5V to 220 ohm resistor
220 ohm resistor to pin 13 - confirmed 5V on pin 13
pin 13 to copper plate
Probe activated as pin 13 active low, port 1
Ground from 5V supply to machine



That looks fine Olf20

The only thing is the BoB ground to machine ground.

If you start to get funny symptoms you may need to disconnect this and use a second wire with a crocodile clip for placing on the tool.

Most likely you won't have an issue.

Active low will be the setting you need.

Greg

Offline olf20

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Re: Auto Tool Zero
« Reply #4 on: December 06, 2008, 12:27:44 PM »
Thanks for the replies. I think I have my head around this.
I just did not want to blow a board, or worse, a computer printer port.
Thanks again for the help!
olf20
Mach3, Atlas Knee Mill, 4th Axis, VcarvePro, ESS, Super PID.
Been Heating with corn since 1998

Online Tweakie.CNC

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Re: Auto Tool Zero
« Reply #5 on: December 07, 2008, 01:08:26 PM »
Hi Olf20,

I have learnt from experience that anything connected to the computers parallel port must be passed through an opto-isolator first. Opto-isolators are usually incorporated on the breakout boards or driver cards - connect through them and not directly to the LPT lead connections.

I have already destroyed one computer connecting a defective coolant switching relay circuit bought on ebay. I am now over cautious.

Regards, Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline olf20

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Re: Auto Tool Zero
« Reply #6 on: December 07, 2008, 08:01:20 PM »
Thanks for the advice Tweakie! I'm going to give this a try tomarrow.

I'm running the signal (pin 13 / 5V and the ground / 0V) in a shielded cable.
That should keep the noise down. Up to now I have had no problems.

Thanks again for all the advice!!
olf20
Mach3, Atlas Knee Mill, 4th Axis, VcarvePro, ESS, Super PID.
Been Heating with corn since 1998

Offline jimpinder

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Re: Auto Tool Zero
« Reply #7 on: December 08, 2008, 03:30:52 AM »
Tweakie - I am not saying that you should't use opto circuits to isolate the inputs to the computer. However - it is safe to plug things directly into the port - look at all the things you plug into a computer. What you have do do is keep within the tolerances of the port.

The only trouble as far as I can see, is that all these isolating circuits introduce complications. I don't think I would worry about the  CNC4PC board and other boards, if the inputs had not been reversed. The input to the computer is designed so that in-going signals pull down the pin to zero - a fairly standard electronic move, and one which many compenents are designed to do, simple to design and relatively safe - i.e. 0v is 0v.

Why then leave all the complications to us - why not replicate this on the breakout boards - i.e. a negative going signal produces a negative going signal to the computer. We on the outside then have all the advantages of component design for our benefit without having to workout how to invert the input.

A very simple example is the opto switches I use on my machine to detect homing and limits. The opto circuit (as bought) is designed to produce a 0v signal, when it detects. It is simple and efficient - requiring the component and a resistor (to regulate the power supply (5v) to the input side) - very fast Scmidt trigger - and accurate to 0.000x of a thou when in use. I feed this directly to my LPT1 - via my breakout board, which is non-powered (just a set of connectors really). Using a powered opto breakout board there would have to be another set of electronics between the switch and the computer,introducing time lag (slight), degeneration of the signal, changes of polarity, etc. - and wait until things go wrong - where is the fault??

My advice is keep it simple as can be - lets get onto manufacturers and have a common standard to work to (much as the railway modellers did in the States) - so that our stuff is really "Plug and Play" - and problems like this can be avoided.
 
Not me driving the engine - I'm better looking.

Online Tweakie.CNC

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Re: Auto Tool Zero
« Reply #8 on: December 08, 2008, 08:06:31 AM »
Well said Jim, I agree 100%.

However, the printer port is fragile - a few mA in the wrong direction by accident and poof.
It's a bit like entering a construction site without wearing a hard hat, now nobody is going to drop a brick on your head are they but is it worth taking the risk ?.
Or like surfing the internet without a firewall, you are not going to get a virus are you but will you take the risk ?.

Regards, Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.