This is one of the early versions of what is now a mature product with over 200+ units in the wild. Feel free to use this in any way helpful (which complies with the CCA license) but if you want the best probing please see
Update 16-7-17 latest thinking on firmware setup can be read here http://forums.reprap.org/read.php?1,767998,page=9
Description (Update History is below)
Following on from the excellent work done by Leadinglights and Moriquendi (http://forums.reprap.org/read.php?1,635075,page=1) I decided to see if I could move the piezo sensor to the hotend, well the cold-end above the heatsink. This would simplify the process of installation, remove the need to suspend the print bed, keep the piezo away from heat amongst other benefits.
Thanks to Xochal for the 90 degree Tee groove mount adaptor this is derived from.
You will need some piezo transducers I used these: Murata 7BB-27-4 As 27mm such as
Place one on a flat hard surface and drill a 4mm hole in the dead centre. It takes a little bit of time, use light pressure and stop frequently to allow the heat to dissipate. Lightly file around the edges of the hole to remove burs. Use a spur point wood drill bit, unless you have something better - let me know.
Print the parts (which will change as I develop this into something smaller and neater). The hot end clamp goes around the groove mount and is secured with m3 bolts and nuts. Make sure the bolts/nuts do not stick out of the clamp get the right length. I am using a bowden e3d v6 hot end which makes it slightly easier to assemble the bowden tube holds everything together. If you aren't using bowden that's okay you'll just have to be more careful.
Attach the bowden tube to the hot end, make sure its tightly inserted with no play, as access to it later is not possible. Place the piezo disc over the bowden tube with the ceramic facing downwards. This has been designed with genuine e3d v6/lite hot ends in mind, the larger push fit bowden adaptors will not fit.
The piezo discs I am using have a solder pad right on the rim of the flange, there is relief in the clamp for the solder pad and wire on the piezo disc.
The upper part needs 2 m3 nuts pressed/heatpressed/bonded into it. Use m3 bolts ideally just the right length (around 15-17mm) to secure the upper part to the lower clamp with the piezo disc in between. Try to tighten them evenly, you do them up quite tight, this will make the nozzle firmer, but the sensitivity will be less, its a balance.
Now secure the leads of the piezo sensor with heatshrink/cable ties to one of these bolts, they are very delicate and you don't want them pulling off in use.
Now you can mark and drill your effector for the two mounting screws both m3.
Attach the piezo to the controller board a design for which is available here https://www.dropbox.com/sh/3q38ew98kt7f8sq/AAB_uA6tQL2ETlGcnfdijm2Ra?dl=0
Moriquendi designed and built this board PM him at reprap forum he might be able to make you one.
The controller connects to standard endstop/probe pins on your board. Make sure +,- and sig are the right way around.
Further details on tuning this board and a little video walkthrough are available at https://www.duet3d.com/forum/thread.php?id=752&p=3 I will update the long post I wrote about tuning there as things develop.
I am using DuetWifi and the controller is analogue so you can use M558 P1 I1 X0 Y0 Z0 and G31 X0 Y0 Z0 P600 in your config.g to set analogue sensor, connected to z-probe pins, and inverted triggering. Use with ramps/marlin I have yet to test but if you have got it working with this setup post the details in comments and I will include them here.
Now probe away, its very sensitive so if you are doing bed level probing set lower speed/jerk settings to prevent false triggers. But it makes sense to probe at around 500 mm/min (8mm/s) so the contact with the bed gives a firm tap. Make sure you set "use for probing only" rather than it being an active endstop as movement of the effector/carriage will cause triggers during printing/travel moves. I found a tiny positive z-offset was required this will be less the stiffer your setup is, but the piezo has to bend so the point where the probe triggers will be slightly lower than z=0 so you need to offset your nozzle upwards fractionally when printing.
Please be aware using this controller, there is no fail-safe operation, if the piezo becomes detached. So it is recommended after powering on your machine just to check the probe, by either reading its analogue value from your firmware idle, and when pushing up on the hotend, or sending m119 and pushing up on the hot end to check it shows triggered.
Latest version draft 5, now very firm nozzle and good clear triggers. Wider and taller flange on the lower clamp parts and slight recess in the upper part. I can't see this version changing unless longer term testing shows a problem, apologies for the rapid changes. Next step a delta effector with built in sensor. One has been created already by Lykle of Zesty Technologies http://www.thingiverse.com/thing:2047422 I am now testing this and it seems to work very well. My calibration deviation is 0.03 with this effector (I was getting 0.014 with my draft 5 version above, but the nozzle is firmer with this version so I am willing to accept the slightly less precise calibration).
3rd Update 16-01-2017
So I have added a subtle lip to the top of the lower parts to both improve clearance over the e3d bowden coupling, and to reduce the diameter of the contact area with the piezo so giving more flex and therefore a stronger signal. I have also cut away a small area on the top section under the piezo for the same reason.
2nd Update 16-01-2017
Slight modification to the lower parts of the assembly to raise the height above the hot end by a small amount (0.8mm) after assembling it I noticed the piezo was slightly pressing onto the bowden coupler and loosening the bowden tube.
Mk II now available, this is a smaller and neater version using all m3 bolts for ease of assembly. Needs plenty of support when printing it.
Please use the shortest machine screws you can for each of the fittings. You need to heat press the nuts all the way into the recesses. Use countersunk head machine screws for the hotend clamp as the top piece fits over it with quite tight tolerances (0.2mm), doesnt matter if its a little tight.
I have allowed a tiny recess for the solder pad on a 27mm piezo transducer.
One of the photos shows the type of drill bit (spur point wood drill) I used to drill the latest piezo, place it on a wood board, mark the centre, then use firm pressure and low rpm to drill, cuts much neater than any previous attempt, hold the piezo firmly with fingers and pause your drilling if its getting hot. Use a needle file to smooth the edges afterwards.