reaction time for z-probe triggers?

I'm installing a home-made piezo zprobe under one corner of my hot-end mount so it is preloaded under the clamping forces. When I tap the nozzle I get a ringing signal that dies to zero quickly. This also makes sense cause the hot-end mount has some compliance with an o-ring I added.
Anyway, the result is (after transistors and such) pulses on the order of 1 ms to the Duet.
Right now I am using 2.0(RTOS) (2018-06-05b3)
The Duet does not recognize these pulses so how much noise rejection is built into this board ie shortest pulse it will recognize.

Also, P8 says it's an unfiltered P5, which is designed for a switch, but I need P1 because my signal is active in both directions.

Edited 1 time(s). Last edit at 09/11/2018 02:18PM by shadowphile.

Which Z probe mode are you using in the M558 command? In most modes the input is filtered, but mode 8 is unfiltered, although the pulse still needs to be longer than the step pulse interval.

Other piezo designs use some circuitry to lengthen the pulse.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I was in P1 but changed to P8 because of the speed but not enough to help.
When you say step pulse you mean whatever is driving the motors? So basically I figure out what that is for the probing speed as a minimum (plus some I'm sure).
I was thinking that I would need to add some kind of pulse stretching.
thanks

Ok, built a new circuit from scratch and now get a 1 second pulse when the zprobe triggers.
It is super sensitive but that means false triggers during the bed probe sequence. Is the trigger monitored all the time during the G30 moves? I would like to only enable the probe right before the G30 command and disable right after to prevent false triggers.
I have a disable pin on the probe but before I bother configuring it with a digital out from the Duet, will it do anything I can use in this case?
thanks

It doesn't matter if it triggers when the machine is not doing a bed probing move, as long as any previous trigger pulse has ended when the probing move starts. You can configure a settling time before the probing move starts, in the M558 command R parameter.

1 second is rather a long pulse. I think we use 100ms on the Smart Effector, but it's only as long as that so that you can see the LED flash.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I have one of the Precision Piezo kits. Theirs are configured for 250ms triggers, which the Duet has no problems detecting at all.

I have my M558 code set up to give 0.5s delay before moving, so that if the printer motion causes the probe to trigger, it has time to settle. My sensors trigger all the time while the printer is moving, which doesn't cause a problem. (I did reduce Z acceleration for Z homing, screw adjustment and mesh leveling to avoid false triggers with the sensors being very sensitive.)

You can probably shorten that pulse length, if you can get to your R-C components, but the longer pulse shouldn't cause you problems if your pre-probe pulse length is adequate. I would suggest a minimum of 100ms + pulse length.

Aside from possible distractions from seeing an LED flash, I don't see a point in a disable pin. As DC42 stated, it only matters if it gets triggered during a probe move. The Duet will ignore the probe as it prints, no matter how many times it gets triggered.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

This is great, thanks for your help guys. Sounds like I just need to change a resistor on my 555 timer to drop the pulse time and it should work! (maybe needs some gcode adjustments). I had no use for the disable pin, it was just available on one of the ICs I used. But I should add an LED because you can never have too many blinky lights!

I really wish I hadn't blown the serial port on my Duet board I can't see justifying the cost of a new board just for that feature.