COM speed - going beyond 250K ? In latest repetier-host in printer settings I see that I can set baud rate all the way to 1500K (from currently 250K)... What is the highest speed that would still work (i guess melzi is the bottle neck?) - would that bring any improvements? https://reprap.org/forum/read.php?292,222370,222370#msg-222370 Wed, 14 Oct 2026 09:42:43 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?292,222370,231295#msg-231295 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,231295#msg-231295 nophead Mendel90 Tue, 30 Jul 2013 20:15:05 -0400 https://reprap.org/forum/read.php?292,222370,231274#msg-231274 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,231274#msg-231274 I tried raising usb speed to 500k baudrate... and it works.
but when printing from pc over usb, repetier host reports quite a few lines have crc errors so it resubmitts them... (and print is 100% fine)...

anyway, i tried printing same gcode (with print speed 150mm/s just to try to reach all limits with printer at 0.3mm/layer thickness) over 250k and 500k (both from same pc)... and i got no difference in total time required for print it...

so i guess i am changing baudrate back to 250k :)]]> weirdgod Mendel90 Tue, 30 Jul 2013 17:48:05 -0400 https://reprap.org/forum/read.php?292,222370,226717#msg-226717 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,226717#msg-226717
I found this on the web:
Quote

But, even with differential data, there are times when single-ended signalling is used in the USB: The end-of-packet is signalled with a single-ended-zero (SE0), namely, both D+ and D- in low state. This state last the time of 2 bits. if SE0 last for more than 10ms it means a bus reset.

This single-ended signalling makes the USB quite sensitive to electromagnetic interference, like those I found recently when a hair dryer motor was causing a lot of disconnects in a nearby USB peripheral. And no common-mode filters can be effectively used because these can degrade the SE0 signal...

This is why USB is susceptible to ground noise. Mixing single ended and differential signalling states is bonkers.]]> nophead Mendel90 Sat, 13 Jul 2013 10:17:06 -0400 https://reprap.org/forum/read.php?292,222370,226675#msg-226675 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,226675#msg-226675
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I can change Melzi to include optional optocouplers (with solder jumpers as alternative).

I'm working on the same for Gen7 and your doing might help getting this recognized as a recommended feature.

The last few days I've read a lot about this topic and the result is, there are not only optocouplers, but also "digital isolators", like the ADUM 1201. Optocouplers are cheaper, but usually also require additional components, like current limiting resistors and flyback diodes (as far as my research goes).

There's even a small chance to get away without any additional parts, because USB (D+/D-) is a differential signal, so it should work without a ground connection. I'll try that today.]]> Traumflug Mendel90 Sat, 13 Jul 2013 07:04:41 -0400 https://reprap.org/forum/read.php?292,222370,226361#msg-226361 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,226361#msg-226361 > Having same that adding ferrites to the USB cable does exactly that. I.e. makes the connection a
> high impedance at high frequencies. I don't understand how that helps and doesn't make it
> worse.
The idea of ferrite is that it affects all conductor the same - there is high impedance in loop closed outside the ferrite core, but "differential" impedance of conductors going through same core is not affected. Passing usb cable through ferrite core decreases high-frequency currents flowing between two grounds but does not affect usb signals (referenced to cable shield).

> I would have thought that putting ferrites on the
> mains cables would make a lot more sense than
> putting it on the USB cable.
The idea is to break the loop, putting it on USB cable is probably better (capacitance and radiated currents skip mains cable).

BTW: If there is interest, I can change Melzi to include optional optocouplers (with solder jumpers as alternative). And add capacitor to 3.3v SD rail, I hate communication reset when inserting SD card.]]> ledvinap Mendel90 Fri, 12 Jul 2013 05:08:34 -0400 https://reprap.org/forum/read.php?292,222370,225525#msg-225525 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225525#msg-225525 nophead Mendel90 Tue, 09 Jul 2013 15:03:53 -0400 https://reprap.org/forum/read.php?292,222370,225521#msg-225521 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225521#msg-225521 [geekboy.it]]]> Anonymous User Mendel90 Tue, 09 Jul 2013 14:59:13 -0400 https://reprap.org/forum/read.php?292,222370,225417#msg-225417 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225417#msg-225417
Having same that adding ferrites to the USB cable does exactly that. I.e. makes the connection a high impedance at high frequencies. I don't understand how that helps and doesn't make it worse. Those ferrites are added to cables to stop high frequency RFI getting from the equipment onto the cable which would then act as an aerial and radiate. They will also stop the opposite of course. I.e. RFI being picked up by the cable getting into the control board and PC. However it isn't the controller or the PC that gets upset. I.e. neither crash or reset (as long as the auto reset jumper is not fitted). It is just the USB protocol that breaks down.

I would have thought that putting ferrites on the mains cables would make a lot more sense than putting it on the USB cable.]]> nophead Mendel90 Tue, 09 Jul 2013 08:16:03 -0400 https://reprap.org/forum/read.php?292,222370,225402#msg-225402 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225402#msg-225402
I also thought about coupling these two GNDs not directly, but via some filtering component (1 megaohms resistor? - 500 kHz low pass filter?), but couldn't find an example circuitry, so far, so I'm not sure if this is a possible approach.]]> Traumflug Mendel90 Tue, 09 Jul 2013 07:41:26 -0400 https://reprap.org/forum/read.php?292,222370,225104#msg-225104 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225104#msg-225104
One of the listed features is: Atmel ATmega 2560 with FT231x FTDI USB chip

Here is the link to the full list of specs.

I love the convenience of printing over USB, but the inconsistency is too much for my taste. It seems like some of the more recent version of Octoprint are also increasing my USB communication issues. Though my experience may not be the same as other Octoprint users. I suspect it is particularly sensitive to comm issues because it sends an M105 every second to keep track of temps and I don't see a way to selectively enable or tune this in the current branch. Though, I still enjoy having the remote interface to initiate/cancel prints from SD and to watch the progress via web cam.

Fl0yd]]> Fl0yd Mendel90 Mon, 08 Jul 2013 10:16:27 -0400 https://reprap.org/forum/read.php?292,222370,225096#msg-225096 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225096#msg-225096 nophead Mendel90 Mon, 08 Jul 2013 09:38:43 -0400 https://reprap.org/forum/read.php?292,222370,225094#msg-225094 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225094#msg-225094 nophead Mendel90 Mon, 08 Jul 2013 09:34:32 -0400 https://reprap.org/forum/read.php?292,222370,225092#msg-225092 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225092#msg-225092
Fl0yd]]> Fl0yd Mendel90 Mon, 08 Jul 2013 09:31:07 -0400 https://reprap.org/forum/read.php?292,222370,225090#msg-225090 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225090#msg-225090
Quote

I find if I plug machine and PC in the same wall socket or extension I don't get any disconnects but if I plug them in to sockets far apart I will get a disconnect every time I switch the fluorescent light in the same room.

This might be the reason why the problem isn't seen that often. Usually, printer and PC are close to each other, so it's likely they use the same mains socket.]]> Traumflug Mendel90 Mon, 08 Jul 2013 09:29:09 -0400 https://reprap.org/forum/read.php?292,222370,225016#msg-225016 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225016#msg-225016
For my machines that use Ethernet I used a micro with built in MAC and PHY so the only hardware is the socket with magnetics in it. They are only $1 in high volume. For software I wrote my own simple UDP/IP/MAC/PHY stack.

I find if I plug machine and PC in the same wall socket or extension I don't get any disconnects but if I plug them in to sockets far apart I will get a disconnect every time I switch the fluorescent light in the same room. I doubt Gen7 is any different as it isn't a board issue. Simply USB cable and ground leads. Also a low impedance PSU DC ground is very important.]]> nophead Mendel90 Mon, 08 Jul 2013 05:17:02 -0400 https://reprap.org/forum/read.php?292,222370,225009#msg-225009 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,225009#msg-225009
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I can't think of any professional devices that use USB and are grounded.

2D printers? Maybe you don't consider consumer 2D printers to be "professional", still they work very reliably. Not sure wether they have optocouplers inside, though.

Ehternet is a different matter. Requires quite a bit of hard- and software.

One thing I'd be interested in is, how much this is really a problem. From Gen7 users I read very rarely about unexpected disconnects. Some people can't connect at all, but that's usually a failure of proper soldering and solvable.]]> Traumflug Mendel90 Mon, 08 Jul 2013 04:40:56 -0400 https://reprap.org/forum/read.php?292,222370,224773#msg-224773 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,224773#msg-224773
To fix it one would power the FTDI chip from VBUS and opto couple the data lines to the ATMEL, thus breaking the ground loop. Alternative use Ethernet as that is isolated by transformers in the sockets. It also has connectionless protocols, like UDP, that don't suffer from disconnect and reconnect issues like USB. You don't need to install any drivers, which seems to confuse a lot of people, but you may have to allow it through a firewall which might be even more confusing.

I can't think of any professional devices that use USB and are grounded. Perhaps some big printers, but I expect they isolate as described above.]]> nophead Mendel90 Sun, 07 Jul 2013 08:41:46 -0400 https://reprap.org/forum/read.php?292,222370,224756#msg-224756 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,224756#msg-224756
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Printing via USB usually works, but will occasionally have errors due to the PC not responding in real time, or it might disconnect if the ground loop picks up RFI.

This is something I'd like to overcome. I mean, USB connected memory sticks and similar stuff work reliable for weeks, so this should be doable for controller electronics, too.]]> Traumflug Mendel90 Sun, 07 Jul 2013 07:24:12 -0400 https://reprap.org/forum/read.php?292,222370,224630#msg-224630 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,224630#msg-224630
Printing via USB usually works, but will occasionally have errors due to the PC not responding in real time, or it might disconnect if the ground loop picks up RFI.

If I am printing a one off I sometimes risk USB, but for production I always use SD.]]> nophead Mendel90 Sat, 06 Jul 2013 14:35:13 -0400 https://reprap.org/forum/read.php?292,222370,224581#msg-224581 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,224581#msg-224581 and once I would go above supported speed, I am afraid printer would stop responding (since i would have no means to successfully connect)... that is why i am rather asking before trying :) you know - to learn from someone elses's mistakes.

i must say that i am using printer host software (instead of pronterface) and am very satisfied with it. + i tried printing a lot of models directly from PC (and not SD card) and it is working very good - with no problems.... (and loading SD card takes ages, or taking it out/in every time is difficult and does not fill me with confidence that meltzi sd card will live long)...]]> weirdgod Mendel90 Sat, 06 Jul 2013 08:46:48 -0400 https://reprap.org/forum/read.php?292,222370,224558#msg-224558 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,224558#msg-224558
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What is the highest speed that would still work

Try it and tell us!]]> Traumflug Mendel90 Sat, 06 Jul 2013 07:04:48 -0400 https://reprap.org/forum/read.php?292,222370,224412#msg-224412 Re: COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,224412#msg-224412 Anonymous User Mendel90 Fri, 05 Jul 2013 14:51:12 -0400 https://reprap.org/forum/read.php?292,222370,222370#msg-222370 COM speed - going beyond 250K ? https://reprap.org/forum/read.php?292,222370,222370#msg-222370 weirdgod Mendel90 Fri, 28 Jun 2013 17:43:18 -0400