Zprobe design module for pcbmill


I am trying to create a module that takes a z-probe reading on a copper clad board at a higher voltage.
Any opinion is welcome.
Zprobe001.pdf (43.3 KB)
716806.pdf (125.1 KB)
838145.pdf (287.6 KB)


Nice idea. I’m assuming you’ve had issues with detection and a little research says this is a proven solution. Are you breaking endmills while probing or getting false contact because of noise? If only the latter it might just need a low pass filter.

I’m going to guess that your circuit could benefit a little from a low pass filtering on the inputs for noise but the hysteresis in the comparator might be enough.

Why did you choose to use two opto-isolators? I’d guess the current drive needed for the TinyG input should be easy to get with one optoisolator. Z-min has a 2.7k pull-up to 3.3v. That’s < 2ma with a max Ic of 50ma on the optocoupler. All that said I’m also not convinced you need the optoisolator since the LM319 is open collector output and the tinyg has a pull-up to 3.3v.

You’ll need need to think through how to power this circuit. I’m assuming it can mount inside the case so you will want to make due with the existing supplies. There is a 24vdc Vmot supply. The tinyg then has jumpers for Vmot (J1), 5V (J11-2), and 12V (J14). The problem with J14 is that the voltage on that connector is selectable between Vmot and 12V using J15. The intent is so we can use either a 12V or 24V fan on J14. Right now we have a 24V fan on J14. So we could move the fan to J1, change J15 to the 12V setting, then hook this circuit to J14. An alternative is to just put a 12V regulator and a couple of caps on your circuit then use the main 24v supply.


MsTovenour i have seen this problem happen. I am trying a solution and posting my findings as i go. I started out with my own assumption and my initial objective was to create my circuit and if it is a success to share it. and if my circuit is a failure to post this and state why. I am trying to restate Some of what you just said. So you MsTovenour are skeptical of my problem? Or maybe you don’t understand what my problem is? I am trying to set up the rest of my experiment and issue my circuits have… I will be doing multiple post to give a more clear reason to my problem. and how i am trying to solve this problem.


Why i used opto couples was electrical isolation. I considered ground currents and decided opto couplers where a good idea. The ground of the pcb and ground of the controller ic could be at two different potentials.

By using two different isolated points of contact i can ensure i can ensure the control board is isolate. Both my pin for reading and my ground pin.


I am sorry there must be a confusion i am not using the tingy. I am using wood pecker board at 15V input. My circuit is design with 15V in mind… I am sorry i was still trying to post all of my picture i will do so probably on Tuesday. I have job interview on Monday.


Thank you MsTovenour. My reasoning for not putting hysteresis into the comparator was because I am not dealing with a analog signal. Rather i am dealing with a nearly purely digital signal thus i should have no analogy chatter. In theory, but this may be a issue later. I would like to first try this circuit with out the hysteresis. Also hysteresis would slow up my circuit. If i do have problem i will fix the circuit and repost my schematic. thank you.


I am working with this…


Perhaps R8 should be turned into a rheostat so adjust probe sensitivity.

The optocoupler are connected to A5.


I only asked because I wanted to make sure I understood the problem you are trying to solve and if it is something you already experienced or something you perceive could happen.


Opto isolators can’t hurt but to truly isolate the grounds you will also need an isolated power supply. Otherwise the power grounds are the same anyway.


How many steps per second are you doing as the stepper drives the bit towards the surface? Check the response time of your circuit.


This circuit if for the zprobe reading… The carbide tip touches the copper clad board. This circuit is to read weather the carbide tip has touch the copper clad board. often the copper clad board comes with oxide on it and thus does not make good contact with the carbide tip.


Also sorry so it is M_Stovenour. I just got off a interview i hope to have a better description tomorrow.


Use a metal puck of known dimensions then subtract it to know where zero is.