Further to my earlier post regarding the noise I see on the 3.3V rail when the bed heater turns off, I disconnected the scope probe that I was using to trigger from the mosfet drain signal and nearly all the noise went away. So it seems that what I was seeing was coupling between the scope probes via the (short) common ground wire I was using to connect to the scope prove earth clips to pin 2 ofby dc42 - Ormerod
Quotedroftarts @dc42: Is it just me, or does everyone else get "Image error, Running getimagesize() on the image data failed" on your pictures? They don't work in Firefox, Safari or Chrome on Mac... Ian RepRapPro tech support Hi Ian, I've complained about it here.by dc42 - Ormerod
If I try to link to my images hosted on Dropbox, then in place of the image in my post I get an "Image error" message. Here is an example: I think this is because Dropbox links are https, and Phorum doesn't understand https. If I change the https: to http: then I get this instead: Is there a workaround? Can anything be done to allow images on Dropbox to work in these forums? I don't want toby dc42 - Administration, Announcements, Policy
Here are my photos of the 5V and 3.3V supplies when the bed heater is turned off (yellow trace is 5V or 3.3V, blue trace is mosfet drain voltage which I used to trigger the scope): This is after I did the mods I listed in my previous post. The 5V and 3.3V transients are not very different, so I believe they are mostly caused either by the scope probe and its earth lead detecting the magneticby dc42 - Ormerod
Radian, I attached a scope to my Duet board to see if I can replicate your observations. This is what I found on the mosfet drain: As you say, there is a 50V spike and the mosfet is avalanching. Here is the voltage on the 12V input, measure directly between the screw terminals: I don't see a 20V spike, the peak is a little under 14V. I did see a bigger spike when I connected the scope earthby dc42 - Ormerod
QuoteRory166 I would like to examine the circuit diagram of the duet but am unable to access through github, possibly due to my use of a Mac. Are you able to direct me to a copy? I need this to use my scope onth eboard to confirm your results are universal. Rory, if you PM me your email address, I'll email you the pdf.by dc42 - Ormerod
QuoteRadian I also thought you'd mention a snubber network across the load ;-) 1uF/10R seems about right 10R would be too low, 2R would be more like it, that would limit the peak mosfet drain voltage to 12 + (2 * 11.3) volts. But since we don't need to reduce the rise time of the drain voltage, just reduce the amplitude of the spike, a flyback diode is simpler and avoids increasing the turn-on tby dc42 - Ormerod
I've completed this mod and it appears to work well. Here are some photos. First, the 59p frame kit: After cutting 4 tabs from the slotted MDF: After lengthening the slots in the bed insulator to 30mm: After fitting the glass, heat spreader and mdf tabs together with the clips: After attaching the bed assembly to the carriage, using 20mm cap head screws and extra nuts: I found that I waby dc42 - Ormerod
The processor has a builtin watchdog timer that can reset the processor if it isn't kicked for a while. It should be a simple matter to enable this in the firmware, along with a status indicator to indicate whether the last reset was caused by power on, reset button, or watchdog. Ian, are there any forums where we can suggest improvements to the Duet firmware, and improvements to the Duet electrby dc42 - Ormerod
If the hot bed takes 11.3A then it deserves some serious decoupling caps right between the +12V feed to the hot bed and the source terminal of the mosfet. As opposed to no decoupling caps at all, as on the present designby dc42 - Ormerod
Arnaud31, just in case the problem is between the router and the Duet, it might be worth connecting the Duet directly to your computer, disconnecting the computer from the router, and manually setting the computer IP address to one on the same subnet as the Duet.by dc42 - Ormerod
QuoteRory166 The mains is full wave rectified and applied to two 470uF 220V caps, in series I hope, through a largish inductor, well thats a turn up for the books, since when was an inductor cheaper than adding more cap? The 2 x caps in series is a standard arrangement for 115V/230V power supplies. When running from 230V, the bridge rectifier works normally, giving about 320V. For 115V, a link iby dc42 - Ormerod
Radian, thanks for the warning about the 20V spike when the bed heater turns off. I haven't looked at my Ormerod with a scope yet. If the 20V spike on the 12V rail only lasts for a few hundred ns, then I suspect it is the result of power circuit inductance rather than the ATX PSU taking a long time to recover. The Duet schematic shows decoupling capacitors on the 12V line near the stepper driversby dc42 - Ormerod
I just spent 59p at The Range on a 10x15cm frameless photo mount. The clips are about 25mm long, 13mm wide at the widest point, and protrude about 8mm below the heater pcb. As suggested by Rory, I'll cut pieces out the mdf that came with the photo frame to put under the heater pcb so that I can lock the clips into the slots in those mdf pieces, and enlarge the cutouts in the bed insulator to suitby dc42 - Ormerod
In the Tools list: - I suggest you recommend having ball-ended 2mm and 2.5mm hex drivers, because there are so many screws and it would take ages to assemble an Omerod using just allen keys - Also useful is a spanner (5.5mm?) for the M3 nuts - I bought the calipers, but never found out what I was supposed to use them for - I also needed a 6mm drill to enlarge the hole in the z-nut trap, howeverby dc42 - Ormerod
In the final 3 photos on the heated bed assembly page, you have the board connectors at the front and the hole for the thermistor wires on the left. This means that the cutout in the cardboard for the connectors is off-centre. This in itself doesn't really matter because it still fits; however if you then line up the cutout in the heat spreader plate with the cutout in the cardboard, then the heaby dc42 - Ormerod
Thanks, 3D-ES! I was going to try to get it building under Atmel Studio, but if Eclipse has Arduino integration (which I wasn't aware of) then I guess using Eclipse will be easier. I'll give it a go.by dc42 - Ormerod
Great idea, Ray! I'll go out and get one of those photo frames.by dc42 - Ormerod
It sounds as though you haven't connected the thermistors to the Duet. Have you plugged everything into the Duet, as shown at the bottom of this page?by dc42 - Ormerod
There are a couple of things you can check: 1. Check that there is a jumper across the "5V EN" pins on the Duet board. See attached photo. If there isn't, DO NOT add a jumper in this position until you have done the next check, or you risk destroying some components on the board. 2. Check that components R60 and R62 next to that jumper are the right way round as on the photo, i.e. at right anglby dc42 - Ormerod
I agree, it doesn't look easy to add a big capacitor in parallel with C3. However, I've found 470uF 25V and 680uF 16V SMD capacitors that will probably fit in the C3 position, and 330uF 16V caps that will definitely fit. I'll add some to my next Farnell order. Or maybe just get an ATX PSU with better resistance to brownouts.by dc42 - Ormerod
Has anyone found a good way to hold the print bed firmly on the heat spreader and not slip? The foldback clips don't work for me even if I just clip them over the edge, because on the end of the bed nearest the Y-motor the fan housing fouls on them, and at the other end the IR sensor fouls on one of them. So only 1 of the 4 clips is usable on my Ormerod. I tried attaching the bed with Kapton taby dc42 - Ormerod
QuoteRory166 Yes I see that using FanO requires 12V, although I assume it would work with a lower voltage than it is intended for(all rails share the same common?). Yes, however according to the schematic there is a led + series resistor connected between +12V and the fan output. So even if you use the fan output to switch the sensor led from the 3.3V supply that is already routed to the board,by dc42 - Ormerod
Quotehughesie I can't wait for the 3 colour head , I emailed Reprappro asking when it would be out and was told not in the near future. I was speaking to a supplier of filament today, and he said he will soon be stocking a PVA (?) filament that dissolves in water. The idea is that you use it to support large overhangs etc. and then dissolve it away. It sounds interesting, but obviously you wouldby dc42 - Ormerod
QuoteRory166 I like Ian's post above which I only read after fitting the cap. Feed the 5v rail from a 5v output of the psu. Let the poor old 12v take a right bashing from the switching transients. For that matter the psu also produces up to 30A of 3.3V so why not use that ? I like the current scheme of deriving the 3.3V supply via a linear regulator from a 5V supply. A linear regulator can pby dc42 - Ormerod
I've been thinking about this a little more: 1. Adding extra capacitance to the output of a switching regulator should be done with care. From the A4403 datasheet: QuoteThe output capacitor determines the output voltage ripple and is used to close the control loop. As outlined in the Control Loop section, the bandwidth has been optimized for an output capacitance of 20 μF. If a particular appliby dc42 - Ormerod
Very nice! Where did you find the design? How long did it take to print?by dc42 - Ormerod
Radian, that's very interesting! One other thing I notice is that the Duet implementation of the A4403 5V regulator circuit omits the capacitor in parallel with the feedback resistor. Although the datasheet says this is an optional component, without it the transient response is worse, and the feedback input of the IC is more susceptible to noise pickup (e.g. if any of the stepper motor cables goby dc42 - Ormerod
Hi Rory. Yes I would expect bright sunlight to be able to overpower a 50W halogen lamp. But it's winter so the sun is not very high, and it was well past midday when I observed the effect. Also my windows are double glazed, and modern double glazing has a thin metal film on the inside of the glass to reflect IR. I'm not even sure the sun was shining directly on the print bed. These factors may eby dc42 - Ormerod
Quotechriscain You could use the FAN0 output on the Duet it's connected to the PWM o/p pin with a mosfet and not used on the Ormerod as the fan is on all the time. would need a higher resistor as it's on the 12v supply. That's certainly a possibility, although I'm a little concerned that unless I load the power mosfet heavily, it might be very slow to turn off - which might not matter, dependinby dc42 - Ormerod