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Precision piezo for a CNC touch probe!

Posted by pferrick 
Precision piezo for a CNC touch probe!
March 31, 2022 06:38PM
Hi all-

I'm a visitor from the CNC world (not yet having taken the plunge into 3D printing). I am working on a touch probe for my mill, and I have successfully integrated a Precision Piezo Universal (V2.85). The long thin ruby-tipped probe in the picture is fixed to the center of a 20mm piezo disk in such a way that any contact of the probe flexes the piezo, triggering the sensor. So that's all great!

Here's the issue: the sensor has a 0.25 sec on, active low output. When I probe small holes, the output is sometimes still low when the probe contacts the other side of the hole. That throws an error in my probing gcode (linuxcnc, btw). I could slow the probing motion down, so that it takes longer than 0.25 sec before it triggers again. But I'm wondering if there is any modification that I can make that would instead shorten the trigger time. My understanding is that the quarter second delay was added to make watching the LED blink easier, but what I'd like to do is remove it. Which brings me to my second issue: the sensor circuit.

I'd also like to 're-package' the piezo sensor on a custom pcb that incorporates (among a couple other things) a wireless transmission of the probe signal. (I'm planning on using a microcontroller for this.) I have the V2.85 board, and having the schematic handy would make both the pcb and the delay mod a whole heck of a lot easier! If someone could hook me up with such a schematic, I'd be extremely grateful.

Finally, many thanks to Precision Piezo for all the hard work that goes into the design and construction of the sensor. I'm sure a lot of you have their sensor on your printers, so you know how well it works!

open | download - wtp_scaled.jpg (227.8 KB)
Re: Precision piezo for a CNC touch probe!
April 06, 2022 07:02AM
FYI, in case anyone else is interested in the CNC touch probe- I am planning on open sourcing any hardware/software that I develop!

Re: Precision piezo for a CNC touch probe!
April 06, 2022 12:19PM
Hello all-

I'm having a bit of a conversation with myself here....! On further reflection, I finally realized that the difference between the V2.75 and V2.85 boards appears only to be:

a) the addition of a power-indicating red led
b) the substitution of an LM324 quad op-amp for the TLC27L4
c) some sort of RC delay circuit to keep the 'trigger' led on for 0.25 seconds

If this is correct (and please do let me know if there are any subtle changes involved in say, the op-amp swap) then the V2.75 schematic (which IS available on the PP site) should work fine with my touch probe.

Thanks again in advance.
Re: Precision piezo for a CNC touch probe!
April 06, 2022 08:36PM
No I am here listening, I built an MPCNC Burley - 550X750X220 This still need some work to become a 3D Printer / CNC router.

Looking at putting a Z-Axis endstop / sensor of some design have not determined what as of this date.
Though the MPCNC router does not really need a Z-sensor the 3D Printer add-on will.
This will allow me to 3D Print large models with larger diameter nozzles.

Edited 1 time(s). Last edit at 04/06/2022 08:39PM by Roberts_Clif.

Computer Programmer / Electronics Technician
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