[KnotsAboutWood]

Hi,

I've found a few posts about setting up a Zero Plate, but I'm having an issue that doesn't seem to be covered.

Following this post by Tulsa Turbo.
http://www.cnczone.com/forums/diy-cn...ero_plate.html

I've wired up a plate to pin 11 (the non 5v side),

configured the ports and pins as shown here

(When I set the probe to active low it immediately tells me that the probe is grounded when I hit the auto zero button)

Added this macro to my auto zero button

PlateThickness = .1045 'Z-plate thickness DRO

If GetOemLed (825)=0 Then 'Check to see if the probe is already grounded or faulty
DoOEMButton (1010) 'zero the Z axis so the probe move will start from here
Code "G4 P5" ' this delay gives me time to get from computer to hold probe in place
Code "G31 Z-0.5 F5" 'probing move, can set the feed rate here as well as how far to move
While IsMoving() 'wait while it happens
Wend
ZProbePos = GetVar(2002) 'get the exact point the probe was hit
Code "G0 Z" &ZProbePos 'go back to that point, always a very small amount of overrun
While IsMoving ()
Wend
Call SetDro (2, PlateThickness) 'set the Z axis DRO to whatever is set as plate thickness
Code "G4 P0.25" 'Pause for Dro to update.
Code "G0 Z 0.5" 'put the Z retract height you want here
Code "(Z axis is now zeroed)" 'puts this message in the status bar
Else
Code "(Z-Plate is grounded, check connection and try again)" 'this goes in the status bar if aplicable
Exit Sub
End If

So now when I click the auto zero button, the machine waits for about 5 -7 seconds, raises .5" and then displays the "Z is now zeroed" message.

Any ideas on why it's not dropping down to find the plate as specified in the macro? Any help would be greatly appreciated.:drowning:

Thanks.

[ger21]

Do you have your machine set up so negative Z moves are up?

This tells it to probe down .5".

Code "G31 Z-0.5 F5"

You'll mostly likely want to increase the probe distance, but I think your Z is setup backwards. If so, you can change it to this:


Code "G31 Z0.5 F5"

[CarveOne]

In my own Mach3 setup the probe signal is active low (green check mark) so that when the cutter touches the plate it closes the circuit.

[restless1]

you might try going into mach and setting up some debounce settings and delays if you have noise it will see it as a satisfied state and jump right to finish of the macro..

[KnotsAboutWood]

Ger21, CarveOne, Restless1

I made some changes to verify what was going on with this macro

PlateThickness = .1045 'Z-plate thickness DRO

If GetOemLed (825)=0 Then 'Check to see if the probe is already grounded or faulty
DoOEMButton (1010) 'zero the Z axis so the probe move will start from here
Code "G4 P5" ' this delay gives me time to get from computer to hold probe in place
Code "G31 Z -0.5 F5" 'probing move, can set the feed rate here as well as how far to move
Code "(past probe)" 'verify that it passed the above code
While IsMoving() 'wait while it happens
Wend
ZProbePos = GetVar(2002) 'get the exact point the probe was hit
Code "G0 Z" &ZProbePos 'go back to that point, always a very small amount of overrun
While IsMoving ()
Wend
Call SetDro (2, PlateThickness) 'set the Z axis DRO to whatever is set as plate thickness
Code "G4 P0.25" 'Pause for Dro to update.
Code "G0 Z 0.75" 'put the Z retract height you want here
Code "(Z axis is now zeroed)" 'puts this message in the status bar
Else
Code "(Z-Plate is grounded, check connection and try again)" 'this goes in the status bar if aplicable
Exit Sub
End If

When I run the macro it basically skips this

 Code "G31 Z -0.5 F5" 'probing move, can set the feed rate here as well as how far to move

I change the retract height to .75 to make sure that it was doing that and not moving in the wrong direction. For giggles I changed the code to a G1 command and the probe unit did go down, now it obviously didn't stop when it reached the plate, but it did move.

Any ideas on why it would skip that line of code with a G31 command? Or any ideas on why the plate would show it's grounded when I set the pin to Active Low?

Thanks for all of your help.

[ger21]

Any ideas on why it would skip that line of code with a G31 command?

I don't think it skipped the line. I believe it's seeing the probe input triggered, probably due to noise.

you might try going into mach and setting up some debounce settings and delays if you have noise

Debounce doesn't affect the probe input, so this won't work.


Before running the macro, go to the diagnostics page and make sure the probe input is working. If it is, then I'm pretty sure it's noise. Most people add a capacitor across the input to get rid of the noise.

[KnotsAboutWood]

Gerry,

Looking at the diagnostics page, I don't see a probe under the input signals, but the Digitize ( first row, seven down) flashes indiscriminately, whether I have the plate touching the bit or not. It does seem to flash a little more often when the plate is touching though.

Is this the light that should be active?

Thanks again,

[ger21]

Yes, it's labeled Digitize on the Diagnostics page. You need to get it to work properly before running the macro.

[KnotsAboutWood]

Gerry,

Thanks for all your help, one last thing, can you point me towards a little more information on wiring up the capacitor? Sorry for the trouble.:drowning:

[ger21]

Unfortunately, I have no idea how.

[KnotsAboutWood]

Ok, hopefully someone on the forum will have an idea.

Thanks again for all your help getting me this far.

[KnotsAboutWood]

Gerry,

After thinking of this for a while, is it possible that I may need to wire an alligator clip from the 5V side of pin 11 to the bit? By having the bit wired, it would complete the circuit when touched, correct?

Thanks

[BanduraMaker]

The problem with using a capacitor is that it will necessarily induce a delay, albeit a short one, on the signal.

The capacitor must be wired across the plate and ground to suppress noise. Check out here: Low-pass filter - Wikipedia, the free encyclopedia under passive electronic realization. You might need to add the resistor in series as well but I suspect it will work o.k. without it.

The delay might be a non issue at the feed rates we're talking about for Z-probing but once you pick a capacitor value, calculate how long it takes to get up to 4v and then calculate how far the probe will move in that time period. For the calculation, you can use a value of "1" for R or even measure the resistance of your wiring. Odds are that if you use a small capacitor it won't be moving very far at all but, too small a capacitor won't kill your noise.

Unfortunately, I can't give you any advice on what size capacitor to start out with but let's think about this for a sec.

47uF is a very common size capacitor. Using the formula in the link with a 1ohm resistance, we get a cutoff frequency of 3.3kHz - pretty high and a time constant of well, 47uS which is pretty fast. That might not kill your noise though.

Adding a 100 ohm resistor in series changes the frequency to 330Hz and your time constant to 470uS. 1000 ohm 33Hz and a time constant of 4.7mS.

5ipm = .083 inches/sec. With a 470uS time constant (let's just guess that one time constant will get you to your logic level) the machine will move about .00004" between when the tool touches the plate and when your logic level changes (assuming my math is correct - I haven't done this in about 20 years!)

I'd start with 47uF and no resistor and see if it helps the noise issue. If that doesn't work, try adding a 100 ohm resistor. Test in the air first to make sure it works!

[BanduraMaker]

Gerry,

After thinking of this for a while, is it possible that I may need to wire an alligator clip from the 5V side of pin 11 to the bit? By having the bit wired, it would complete the circuit when touched, correct?

Thanks

I'm not familiar with your board but with a gecko, the touch plate is wired into an input that floats high and the bit is wired to ground (not +5). The mach 3 input is set to active low.

Edit - your mach 3 settings don't have active low set on the input pin. That's probably your problem.

[KnotsAboutWood]

Andy,

Thanks for the information. When I set the pin to active low it gave the message that the plate was grounded. I'll try it tomorrow, but do you think there's a chance that running a wire from the 5v side of pin 11 to the bit might alleviate that problem?

Thanks,

[WoodSpinner]

Andy,

Thanks for the information. When I set the pin to active low it gave the message that the plate was grounded. I'll try it tomorrow, but do you think there's a chance that running a wire from the 5v side of pin 11 to the bit might alleviate that problem?

Thanks,

sounds to me as if there is no pullup resistor on pin 11 of your board, you could check to see if any of your other input pins are at 5v+ with a dmm and use one that is if there are any.
would explain the message you get when you set it to active low.

John

[BanduraMaker]

I'm not familiar with your BoB so I can't say for sure, but it looks like it could be possible that there's an active high connection and an active low connection.

i.e. it could be that the way you have it wired, you must pull the pin to +5v to activate the signal and perhaps the other pin is indeed the one you want to use to pull to ground.

When it doubt RTFM

[BanduraMaker]

sounds to me as if there is no pullup resistor on pin 11 of your board,

Yea, if you look, pins 10 and 11 both have two connections. Could be that one has a pull-up and the other doesn't.

edit: or, it might be that the +5v pin is just a handy +5v connection. Putting a pull up resister from there to pin 11 would do the trick.

[WoodSpinner]

Yea, if you look, pins 10 and 11 both have two connections. Could be that one has a pull-up and the other doesn't.

edit: or, it might be that the +5v pin is just a handy +5v connection. Putting a pull up resister from there to pin 11 would do the trick.

if you stare at the image of that board, it has a jumper labled inputs, and 1,2=pulldown and 2,3=pullup, jumper appears to be on 1,2=pulldown I think this is a clue that the op should dig out the manual on that board

John

[KnotsAboutWood]

Wood spinner,

I'll admit right out that Somewhat electrically challenged, but after looking at the BOB, I saw what you were talki about. So wanting to do some research I found this small snippet out on a site.


Let's say I have a microcontroller (MCU) with one pin configured as an input. If I don’t connect anything to the pin, it is considered floating. This means the MCU might have a difficult time reading the state or voltage on the input pin. A pull-up or pull-down resistor will hold the pin to either a high or low state, while using a low amount of current.

Pull-ups are common on most input logic lines, two-wire (I2C) lines, reset lines, et al. An application of a pull-up resistor is attaching a button to an input pin.

With a pull-up resistor, the input pin will read a high state when the button is open. When the button closes, it connects the input pin directly to ground, thus reading a low state. For this discussion we are ignoring the debounce of the button.

So you're thinking that I should change the jumper on the BOB to set the inputs to pull-up? And then change the pin to active low?

Thanks for your help,