GND and LED- are directly connected. However, PZ- is not connected to GND, you'll find the schematic on the Precision Piezo site.

Idris

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{Precision Piezo} Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters.

Looking at the 13/09/2016 schematic it shows a 1kOhm resistor going to ground. I think a shielded cable from the piezo to the board would aid in noise reduction as well as a shielded one going to control board. The cheap PLUS are quite noisy so some ferrite beads could be useful. Don't have a scope do do any real analysis. BTW, am interested in your adjustable mounts for the piezo underbed mounts. Where is pin 1 ?
S

Earlier boards had a resistor between LED- and GND, boards from v1.1 on do not.

Idris

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{Precision Piezo} Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters.

I got 15 piezo's all from the same suppler and used 4 on my under bed setup an 2 off the where reversed polarity.
Simon it may be a good idea to mention this in the fitting instructions?

Hi, I did its on page 4 under "Instructions Electrical 4)"

Maybe I need to make it more obvious.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I do apologise. I must have missed it unless you have changed it since I fitted mine

Thats okay no one actually reads the manual... Neither do I.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Women do manuals men dont. That what the Mrs say and in my case true in most cases

Been printing fine for 10hours + today before I decided that it was time to replace my part cooling fan as the bearing was running out. So naturally it was some wiggle to the hotend again and now I lost sensitivity again. Went over the pots again (I left VR1 at 0.8Mohm but I even tried 0.9 and 0.6 again just to test the difference) and I checked VR2 this just in case I hit them accidentially when doing the fan work. Yesterday it was probing consitantly at -0.1mm but now it's -0.3mm and I can clearly spot movement in the Aero when it's probing and that was not possible yesterday. So I used some force on titan again moving it some around and then it seems to change to -0.2mm again and slightly more sensitive but not like yesterday. Is there anything in the piezo that can be partly damaged from me moving it to much? Before I got it working I had quite some head crashes bending it some ^^ I tried adjusting more sensitivity to the sensor and reducing the trigger to as low as 200 (had 400 yesterday) in the duet firmware. Also increased speed from 300 to 400mm/min to give it some more "knock" to detect on.


Just for fun, here are a video of the sensitivity yesterday. I'm tapping gently on a lamp that's connected to the desk the printer is standing on. To make it even worse to detect the printer has rubber feet to absorb vibrations. It still detects perfect when I'm tapping the lamp tho Really amazing how much it can detect when it works properly!

[youtu.be]

They're quite hard to break apart from the solder connection on the piezo, more likely you cracked something else on the machine which now means the nozzle isn't contacting bed as firmly or maybe the pots have drifted.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
They're quite hard to break apart from the solder connection on the piezo, more likely you cracked something else on the machine which now means the nozzle isn't contacting bed as firmly or maybe the pots have drifted.

I can see the whole mount bending up before it triggers so it's for sure lifting. And as you can see in the video yesterday it triggered when tapping on a lamp connected to the desk the printer is standing on. Now the led doesn't light up when i tap the printer itself. It lights up if I tap the titan aero tho but it's way less sensitive then yesterday. The pot's I re measured again and VR1 was exactly at 0.802Mohm where I left it yesterday and VR2 was on/off with the light as it should and I even measured it setting it to 1.5V like Idris suggested yesterday to check that I didn't mess up something.

It could be the wires comming from the sensors as they are running pretty close to the fan but they do measure 0.1ohm both when i measure from piezo to connector pins at the PCB. It reminds me a lot on how it was before I changed polairty yesterday actually.

Again, this is most likely me messing something up. The product is fantastic when I got it working properly last night but I must have done something when replacing that fan..

I hope you get it working the mechanical design and tweaks to that probably takes more time to become familiar with than the electrical side which is fairly straightforward and very reliable.

On my corexy for example my z axis is just too mechanically noisy for underbed sensors but hotend sensor modules or titan brackets work just fine.

Edited 1 time(s). Last edit at 08/20/2017 09:50AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I've come to the conclusion that it must be something with the epoxy or sensor itself since it stopped beeing sensitive after I worked on the mount. Ordered 20 new sensors for testing. If it's not that I will try with a new board from you. Until then I've set offset to -0.3mm and it's doing the job. Just annoying to not know why it's acting up like that when it worked so fine for many attempts and tweaking after we got the polarity correct the other day.

Very nice product and I think I will get one more for my corexy build as I love the idea with the hotend itself as probe.

Edited 2 time(s). Last edit at 08/20/2017 11:34AM by minim.

IDRIS

OK, that schematic must be for V1.22 board and pins 5,6,2 are ground and a good place for the shielding connection. Is there a pcb for discrete Components? Suppose I could breadboard the circuit. Would be nice if the schematics were identified with the board versions.

Steve

Edited 1 time(s). Last edit at 08/20/2017 03:42PM by Chowa.

On current boards (v1.22) only GND and LED- are connected to GND.

The schematic contains everything you need to breadboard the circuit. I'm not sure what you asking about with discrete components, if you want to build your op-amps out of individual transistors you're a braver man than I am, that's the only way to get more discrete than the current circuit.

Idris

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{Precision Piezo} Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters.

I was referring to not use surface mount components, rather than thru hole mounted and soldered. Perhaps bad choice of words

Edited 1 time(s). Last edit at 08/21/2017 08:13AM by Chowa.

Ahh right. I never made a through hole PCB, I went from breadboard to stripboard to SMD PCB. Still there's nothing to stop you, the opamp (TLC27L4) is available in a DIP package, that's the only critical part.

Idris

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{Precision Piezo} Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters.

What is the best aproach for gluing in a 27mm piezo disk in the titan aero mount? CA and just two dots at front/rear or all the underside?

I think I used CA glue / superglue and just placed a thin layer on the underside of the disc and pressed it home for a few seconds. So long as it can flex it should work.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

NEW STOCK ANNOUNCED

So we now have Piezo20 Modules in stock - in custom colours....

And Piezo20 PCB's if you want to build/print your own.

[www.precisionpiezo.co.uk]

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

bummer.. They managed to send me 27mm piezo discs without leads.. 20mm ones are with leads tho but can I solder on leads myself? Won't the heat ruin the piezo disc? I can cool it instantly with compressed air or smt if that helps.

Yes I had a pack of the ones without leads too. Sold them on eventually.

You can solder them, its a bit fiddly, cooling it afterwards is a good idea. Test them afterwards on a volt meter on AC volts, just give it a tap you'll either see voltage or nothing.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I bought 20 pieces without leads and 10 of the 20mm ones with leads

It was easy to solder on and it still works after I did it. Bumps 3volts with a little tap on it. It also seems that the polarity is dependant on the way the sensor is used. If mounted in my Aero carriege the positive voltage is at centre and negative on the outside ring. If I turn it and tap the other direction it's the other way around. Will be fun to see if this solves my sensitivity problem or if I do have to get a new controller board. New mount is in the making now with only minor changes in the design. The gap is a bit wider, I moved endpoint to have the weak link in the middle of the mount and I moved the sidewalls to the centre of the screws instead of all the way to the back just to have it tilting more inside the piezo element. Not really needed as the old mount was super sensitive when it was working but I figured I could change it a little bit to be able to lower sensitivity more.

New:

Old:

Not a very scientific test I know, but I've been playing with thes 20 vs 27mm sensor hooked up to the scope at the same time. If I where to guesstimate the 27mm disc looks twice as sensitive as the 20mm disc when it comes to voltage level on changes. It's not very visible if tapping gently on the chair but with some harder taps it's really visible that it goes higher. Added two photos just from testing but it would be more visible showing it on a video or testing it in person I think. All they joy one can have from a geeky experiment while waiting on the mount to print




Edit: Here is a drop test of 1.7 gram from approx 1cm height on both discs. 27mm is the one with highest peaks. This repeats itself over many tests. Not a very scientific aproach I know but I think it shows that that 27mm will give much more resolution.





Edit2: sorry, since the 27mm disc went out of range I did a new one with 10volts per cell in similar drop test of 1.7gram weight from 1cm. It generates over 20 volts vs the 4.2 volts from the 20mm disc. So not just a little more but a lot more My old disc did not give me these numbers so I'm looking forward on testing this one on the pcb.


Edited 2 time(s). Last edit at 08/25/2017 08:43AM by minim.

Looks good wish I had a scope like that

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
Looks good wish I had a scope like that

If you know what you measure you can use your soundcard and a open source program. Only need to watch not to hit to High voltage level on the input

Mounted the new sensor and it's day and night compared to the old one. I had sensitivity set at 0.8Mohm but had to drop it to 0.25Mohm and maybe even more since it was to sensitive. Probes with barely touching the bed like before this started acting up. Now I just hope it stays like this.

Should do as long as you don't tinker with it too much... Which is hard to do.

Edited 1 time(s). Last edit at 08/25/2017 10:04AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

No I tamper with this all the time Next up is bondtech remote extruder I think

Let me know how you get on, I fancy a Bondtech, been watching them on ebay, don't fancy paying full price.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

The piezo changes polarity dependant on which way it's flexed. As you can see from your scope readings the output swings above and below zero. If you were to turn the piezo over and drop the weight on the other side you would see the voltage drop down below zero then rebound above and oscillate. We ascribe the polarity to the signal to suit us but really it's arbitrary, press on the other side you get a reversed signal, swap the wires round you get a reversed signal.

While you're playing with it remember that it's not the voltage that triggers the circuit but how quickly the voltage changes, a tenth of a volt change will cause a trigger if it happens fast enough.

Idris

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{Precision Piezo} Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters.