Zero Touch Probe problem - Page 2

# Thread: Zero Touch Probe problem

1. The jumper is set to pull down for all pins (10-13 and 15) John

But I don’t understand well the wiring from Fig 3. One end of the 1K resistor will go to pin 15 and the other end? Where do I get the +5V?

Since pin 15 has already +5V perhaps I connect one end of the resistor to pin 15 and on the other end of the resistor I connect the probe?

I don’t have 1K (1000 ohms?) resistor but I do have 1.0 ohms, 36 ohms 10W, 33 ohms 1/4W, 3.3 ohms, 3.1 ohms, 10K ohms and 13 ohms 10W. If it must be 1K, I will go tomorrow to the store and get one, hopefully they will have one otherwise I will have to order some from the web. Any particular wattage for the 1K resistor?

2. Hi Nicolas

the +5v is one of the 5V terminals on either side input terminal 13 that your using for the probe

any 1/4W resistor from 1K to 56 ohms will do

the resistor needs to have a low enough resistance to pull the input up to a minimum of +2.4V ( 3 to 4v is better )

4k7 would just work ,
too low a resistance will take a larger than needed current from the supply and run very hot
a 5 ohm 5 W resistor will take 1A

looking at the resistors you have
the 36 ohms is the lowest resistance I'd use
5/36 = 0.136A
5 X 0.136 = 0.7 W

as a test , three 10 K resistors in parallel gives you 3K3

using a 3K3 1/4 W resistor and the 4K7 on board pulldown resistor

(5v X 4.7) /(4.7 + 3.3) = 2.9V at the open circuit input

a 1K resistor gives you 4.1V at the input
(5V x 4.7)/(4.7 + 1) = 4.1V

John

PS
is the ground wire from the breakout board insulated from any eathed part of your machine

if there is a connection between the B.O.B's ground and the protective earth / ground to the machine
you can have noise problems due to the earth loop

3. Sorry John, not clear how to connect the resistor. Is the attached schematic ok?

I don’t know if the breakout board has a ground wire. As far as I know there is no wire from the board that I connected to any ground and the board is mounted on a piece of plywood so it does not touch the panel.

4. Sorry John, I did not see the schematic you provided. Now all is clear

I will give it a try with the 36 ohms resistor I have but tomorrow I will zip to the store and get the one you recommended

Thank you

5. Hi Nicolas

not shure why but last time it took several attempts to attach the diagram

using the same resistor I have another version of the circuit

this time the input pin (13) goes high when the probe makes contact

John

6. John you are a genius!!! Just gave it a try with my 36 ohms 10 watts resistor and finally it works beautifully. Thanks so much

But since the Z axis operation is so critical, I will go to the store tomorrow to get 1000 ohms resistor; is there a wattage range for this resistor? And volts? I understand the resistors come in various watts / volts. Please give me a range of watts / volts because that store has limited supply of everything.

If that store does not have any 1000 ohms resistor then I will order one from the web.

What will happen when I operate the probe in the mean time? I mean perhaps the resistor may get too hot or something will burn or blow?

Thanks again so much for the help

7. Hi Nicolas

Great , just the result we want

its just a matter of having the probe pulling the input in the opposite direction to
the on board pullup / pull down resistor
(not always easy see if you spend too long looking with out a break )

the resistors maximum voltage is not going to be an issue since the circuit only has a 5V supply

using a 1/4 watt resistor any thing from 120 ohms to 1000 ohms will be OK

with 1/8 watt resistors use 270 ohms to 1000 ohm resistors

(the values are high enough not to run the resistors at the maximum wattage
I aim for 70 to 80 % of the maximum )

if your local store is like the Tandy ( Radio Shack) stores that used to be in the UK

then 1/4 W resistors like this will be OK -

E3 Series 480 piece carbon film resistor kit | Rapid Online

or 1/8 W resistors like this :-

http://www.rapidonline.com/pdf/64-0014e.pdf

the 36 ohm 10 watt resistor you are using should ony be warm if the probe is permanently in contact
with the touch plate

( 5/36 ) X 5 = 0.69 W

which is only 6.9% of its maximum (10W)

John

8. Looks like John the resistor I have now will be just fine since the probe is used only a few seconds per day. But for added safety, you provided enough information to buy the proper resistor

Thanks so much for your time and the nice schematics

9. ger21

Unless your board is shorted internally (highly unlikely), imo the "Limit Switch Triggered" message indicates a noise issue
Then I re attached the existing cable to the probe. As soon as I attach the alligator clip to the bit message says either "Estop" or "Limit Triggered" Every time I do this, the message alternates to one or the other.
How about the possibility of a external connection changing the pin state on all outputs at once?
I know it's hard to tell without a complete schematic, and software configuration.

This thread is not finished yet.
What do you think?

10. Am I correct here?
You are connecting 5V+ through a 56-1K resistor then connected to the tool bit.
Your plate is connected to pin 13 on the BOB.
when the tool bit makes contact with the plate pin 13 goes high.
I'm having a hard time seeing how this works.

11. yes

thats what the diagram in post 17 shows and only works when the spindle is insulated
and the jumper set to pull down the input via the 4K7 resistor on the PCB

the added resistor is optional and protects the +5V supply from an accidental short circuit

John

12. You are connecting 5V+ through a 56-1K resistor then connected to the tool bit.
Your plate is connected to pin 15 on the BOB.
when the tool bit makes contact with the plate pin 15 goes high.
I'm having a hard time seeing how this works.
You are connecting 5V+ through a 56-1K resistor then connected to the tool bit.
Why are you connecting this 5V+ to ground ? Seems to me that this maybe the reason why
the EStop and limits are tripping. because its pulling all the outputs low on the input header.
I do not believe that this is a noise problem.
The error message about Estop or Limit trip error message shown depends on which Mach recognized first.

I'M assuming that you have 5V+ connected through the Estop switch then to pin 10 on the bob.
I'M assuming that you have 5V+ connected through the limit switches then to pin 13 on the bob.
These connections have no current limiting resistor. Why aren't these getting hot ?
Why Use such high wattage resistors in a TTL level circuit ?

Shouldn't the solution for fixing one problem not create another problem ?

When I identified this problem ( Post # 7 on this thread)
I didn't have to explain my how I would approach solving your problem.

There is more than one way to fix most any problem, it's up to you to decide which approach to take.

Attached is a schematic of what I would do it.

Probe.zip

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