My improved Probe Circuit

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Joined: Sat Jul 05, 2014 11:55 pm

My improved Probe Circuit

Post by cncdavid » Thu Jul 10, 2014 7:09 am

Hello Forum,

I have made an improved probe sense circuit..

It is vary simple,
I use a piece of microphone coax cable as the probe lead (nice and flexible) and energize it using 250 ohm resistor from V+, At the probe i have another 250 ohm resister from the center conductor to screen (earth).
Then i look at the voltage,back at the coax side of the start resister , if it is 1/2v+ all good, Less than 1/3v+ probe is touching , greater than 2/3v+ there is wiring or connection issue so Estop the mill.

Mach3 can do some strange things if the probe is touching when the probe is called like "ignore the probe and smash the tool"

I did this because i had some issues of false probing caused by interference and i also had my probe not connect once smashing my $100 milling cutter, I never found why it did it so i went about fixing so it would not happen again.

If any one wants the circuit or board then i will name the parts and make all the values correct for release.

Kind Regards

Posts: 6
Joined: Thu Apr 17, 2014 4:33 pm
Location: London

Re: My improved Probe Circuit

Post by paulnd » Thu Jul 10, 2014 4:20 pm


I'll be grateful if you can share your circuit please.



Posts: 8
Joined: Sat Jul 05, 2014 11:55 pm

Re: My improved Probe Circuit

Post by cncdavid » Fri Jul 11, 2014 10:41 am

HI I have attached the files, sorry they are a bit messy they were not designed for release!
Also this is the latest version of the probe board and i have not installed this in the mill yet but it should work i did not change much.

Also the 250R resistor value is not critical as long as the same value is used at the probe end as well and it needs to be a 1watt resistor.

The board uses SMA connectors as I run the small Teflon coax around inside the mill to a BNC for the probe to plug in to.

The Estop pulls low on fault but this may not work in with the way other people have there Estops arranged.

All my Estops come together in a PIC micro-controller which filters them before delivering the signal to mach3, this removes any false triggering and makes it easy to combine different signals.

The 555 timer is to hold the signal long enough to hear it on the buzzer and also guarantees mach3 to see it.

The circuit seams to run fine of the PC power supply.

You can adjust the value of R5 in the divider network reducing the value will make the circuit more sensitive
and increasing the value will make the circuit less sensitive, but it should be fine at 1/3 1/3 1/3

keep the probe sensor board as close as possible to the PC to stop interference between the board and printer port.

always use coax as far as possible and keep the sensitive area or tool as small as possible to reduce the aerial effect.

There is a 100UH inductor at the front end to help remove Radio frequency interference.

I used op-amps and 555 timer because they are faster than a micro-controller through you could easy use a micro-controller ADC.

Disclaimer: Please use the circuits and information as ideas only and at your own risk!

Kind Regards
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