Quoteauser Just my 0.02: I think soldering one wire should be ok for almost everybody operating a reprap I know, it's very tempting to think so but it's just so tantalizingly close to being a plug & play fit that conforms to the skill set needed to assemble the standard Ormorod kit. I wonder, do any other RepRap kits require soldering work? The following plot may be of interest - it's a setby Radian - Ormerod
The aim is to minimise the surface area of the electrical connection from sensor to PCB to minimise stray capacitance (unwanted coupling) I think this pretty much rules out everything except a thin wire. Termination would be a doddle if soldering skills were available but I think mechanical termination would add too much unwanted surface. If the X carriage base is reprinted to include a 2cm squaby Radian - Ormerod
I've put a short video showing the calibration and operation of the capacitive Z-probe on Vimeo: Capacitive Z-height sensing My conclusion is that out of all the technologies considered, capacitive sensing offers the best non-contact solution both in terms of cost and performance. To summarise my own opinions on the alternative technologies tried so far: IR sensing is limited by ambient lightby Radian - Ormerod
Quoteormerod168 QuoteRadian...Because the bed lifts when hot (I've seen as much as 0.5mm rise).. with all due respect, I seriously doubt that, I see, 0.2mm tops and I still doubt my x-axis on that one, some evil forces most be at work me think... Erik Thanks Erik, I was very surprised myself - but knowing how unstable the MDF bed was it didn't prompt me to go looking for another cause. So onby Radian - Ormerod
Hi dc42, I was hoping you could accommodate cap. sensing on your board. It's certainly working well for me. I've even got it to light the status LED I added when the nozzle is at Z=0. The calibration process provides for this as the maximum should be set when the nozzle is fully homed and the sensitivity is such that this position can be discriminated quite well. It provides a bit of an eye-openeby Radian - Ormerod
I dare you to print those in "Flamingo" Dave I just got a delivery from 3dfilaprint and can also vouch for the quality of packing and delivery speed.by Radian - Ormerod
Chuffed you should be - that's a good job all roundby Radian - Ormerod
Quotekwikius The only bit I'm not getting is why the values change dependent on the machine are unknowns.... Hi Andy, thanks for raising this question. You're quite right that many of the variables are known - the current injection is well maintained by the CSM in the PIC , and the area of the plate can be made precise using a PCB. The bed glass, on the other hand, may vary in thickness and mateby Radian - Ormerod
Re: Capacitive Z-height sensing Quotedmould ...you could enable "calibration mode" by detecting when the capacitive sensor is touched with a finger 3 times quickly (say within 1.5 seconds). OK, that passes the "clever test" with flying colours I've already improved the max/min detection by passing the values through an exponential moving average IIR filter with long time constant. The valuesby Radian - Ormerod
OK, I could do with some clever suggestions here - In the PIC firmware the capacitive sensor module yields a 16-bit value corresponding to the height above the bed. This range has an offset, so for example it might be 17000 closest to the bed and 13000 when a few cm away. So while I could just divide by 64 (to convert the 16-bit input to the 10-bit output range needed to feed PWM derived analoby Radian - Ormerod
Quotedc42 I've just spotted a design issue that may affect the thermistor readings. The 1K reference resistors are connected directly to the 3.3V supply, however the VDDANA and ADVREF inputs to the chip are both connected to 3.3V via LC networks. So the voltage on VDDANA and ADVREF will be lower than the voltage feeding the 1K resistors by the voltage drop in the inductors. This will cause the thby Radian - Ormerod
Quotebobtidey Quotedmould [ The only other issue is that it will conflict with the modification of putting the aluminium plate under the bed heater instead of on top. Dave (#106) Having done the mod where the spreader is below I was interested in that point as well. I wonder whether the PCB tracks would do the same job anyway as they should be effectively a ground plane for AC. True, the heateby Radian - Ormerod
Quotedc42 I've given this some more thought, and I'm going to hack one of my sensor boards to try capacitive sensing. It should be possible by omitting some of the components for the ultrasonic sensor and changing some others. I'll use Atmel's capacitive transfer technique. The main issues look to be mechanical, i.e. how to mount the foot. One possibility is to make the printed insulator that I mby Radian - Ormerod
Quotedmould One thing I could think might affect the readings is the presence of people or other objects around the printer - did anything nearby move when you saw the reading jump? The other thing is whether the readings are the same for a given height at all places over the bed - if not it might require a different parameter to be set for each probe position. Hi Dave, fortunately the capacitiby Radian - Ormerod
Your timing is perfect Dave - I have some white Ninjaflex on order to try out. I saw adafruit using it for LED diffusers: and fancied a go. Your final print looks fantastic!by Radian - Ormerod
Well, this isn't helping: Dumping the values I was putting into the PWM generator I could see they were much less noisy than the Zprobe readings after being A/D converted by the Duet. So I hooked up a couple of 1.5V batteries in series with a 100R (100uF/10nF in parallel with output) to the input of the A/D and measured 200 seconds worth of readings. This will come as no surprise to dc42 who wby Radian - Ormerod
colsenfoto - thanks for your encouragment OK, so I've got filtered PWM giving a 0 to 3.3V Z-probe height form the CSM counter. To get sensible scaling I'm tracking the minimum/maximum counts found while moving Z and scaling the value sent to the 10-bit PWM generator accordingly. So here's the numbers from the web interface: Z Zprobe 0.0 1010 0.1 990 0.2 908 0.3 844 0.4 760 0.5 701 0.6 667 0.7by Radian - Ormerod
kwikius, your plan makes use of a capacitive divider then. The Capacitive Sensing Module I'm using in the PIC chip uses a cute scheme where an internal constant current sink and source alternately charges and discharges the sensor plate generating a triangle wave that varies in frequency with the amount of charge taken by the plate. In this case the aluminium heat spreader makes a great groundby Radian - Ormerod
Unless I'm misunderstanding you, the heat spreader has such a large area it's pretty much already at ground. No chance of using it as the waggling end. In fact, I see no change in frequency if I croc. clip it to 0V. That's why I waggle the postage-stamp sized foot above it.by Radian - Ormerod
Hi dc42, Input: A = 20mm x 20mm square of tin, D = 3mm above glass (K=5 ?) C=K*Eo*A/D, =5*8.854x10-12*0.0004/0.003 =6pF Not much on paper, agreed, but all in a day's work for a half-decent CSM like the one in the PIC I'm very keen on getting it to work reliably with the stock glass, but yes, coated glass would totally transform the situation. Mind you, in that case we could just dangle aby Radian - Ormerod
In the continued quest to develop a better Z-height sensor I finally got around to testing a capacitive sensing probe. The principle is simple enough - create an oscillator that varies it's frequency with changes in capacitance in part of its circuit. By using the alluminium heat spreader as one plate of the capacitor and a square of tea-caddy tin under the X-carriage as the other, I'm generatingby Radian - Ormerod
Not so easy to get hold of a 320kHz source and as you say Flyskyhy, the wavelength drops to 1mm so finding the right maximum is going to be all but impossible. Echo timing might be a better proposition but the ring-down for this frequency would still be subject to too large a blindspot. 30mm seems to be the ballpark figure for commercial U/S range detectors.by Radian - Ormerod
Thanks for the encouragement Ray... I've gotten into the habit of doing rather than thinking since I noticed my thinking was slowing with age. One advantage I've noticed is that unexpected results sometimes provide pointers to better solutions. Sometimes it just results in a face palm. I just put a new post in the Ultrasound thread for you karabas:by Radian - Ormerod
Hi karabas, my printer has all original parts made in PLA so I've not dared use high bed temperatures even for testing. Air is a pretty good insulator though - if you could monitor the temperature at your IR sensor location (about 3mm above the bed) with the bed up at 120c that would be interesting to know. Otherwise we're just guessing really, but you would need to make sure the air was very stiby Radian - Ormerod
Quoterayhicks because it might scrape up some of the print? - mind you a large diameter ball-bearing constrained in a tube, and pushing on the the switch wouldn't... Ray Haha! So that's why! I've been air printing for too long while playing around with the Ultrasound.by Radian - Ormerod
Quotekarabas I never cool the bed between prints just replace glass. That is why I need any reliable Z sensor. Just for kicks, I stuck a limit switch from a scrapped inkjet printer on the hot-end assembly and it seemed to work just fine. Someone remind me why a dumb switch isn't good enough?by Radian - Ormerod
QuoteKimBrown I have a great respect for the guys above.... But.... One central thermister won't work. The reason is, as good as they are the Bed Resistances aren't going to be matched to well. Your better having 4 thermisters, each controlling one Bed. Likewise (for the above reasons) connecting Beds in series is going to Magnify the problem. The Bed with the Lowest resistance is going to be theby Radian - Ormerod
Hi karabas, good time for a summary so far: the two-transistor circuit I posted above has been Z-homing my Ormorod directly in place of the original IR sensor board since I put it together last week. I would say it's very reliable at low temperatures (<70c) but the effects of air temperature become more and more pronounced as it increases due to air movement. The circuit makes use of a handfby Radian - Ormerod
As it's your topic Ray, I'll post this here - although it's not related to the slide bearings, but to your digression towards larger bed sizes... In case you didn't know it already, the Duet has a provision for an external switching transistor (MOSFET). These are typically cheaper than electromechanical relays and have far superior characteristics for handling high currents. The other bit of magby Radian - Ormerod
Quoterayhicks I should be able to do an A4 sized print bed pretty easily in the current frame, when I get round to X and Z I intend using 500mm extrusion there too, but will have to look hard for a heated bed big enough to use that much space. Ray, I keep trying to track down a supplier of Carbon Fibre heating tape. It's used in lots of 12V and 240V heating applications - like heated seats, gloveby Radian - Ormerod