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RAMPS for BeagleBone

Posted by cdsteinkuehler 
RAMPS for BeagleBone
February 05, 2014 06:43AM
I am working on a BeagleBone Cape version of the RAMPS design, called CRAMPS. I have a stub page created in the RepRap wiki, and KiCAD design files are on github. The design is based primarily on the RAMPS-FD, with changes where needed for the BeagleBone.

The schematic is mostly complete except for assigning some I/O on the BeagleBone P8/P9 pin headers, which I will do based on the PCB layout (in progress). I would appreciate any design review or comments on the schematic.

Features are pretty much identical to the RAMPS-FD, except for the AUX expansion connectors. There is an SPI interface available that will work with the RAMPS-EXT extruder expansion boards, and an I2C header. Both the I2C and SPI headers are 5V tolerant, to allow easier interfacing to existing 5V Arduino add-ons. I plan on using pass-through connectors to support additional expansion, so the large AUX4 connector has been removed, and the AUX2 analog connector has been modified to allow direct interfacing to a 4-wire resistive touch-screen.

Questions and comments welcome!
Re: RAMPS for BeagleBone
February 09, 2014 09:53PM
After struggling to come up to speed with KiCAD, I have an initial verison of the CRAMPS board ready for FAB (checked into github. I will do a final DRC, manual review, and check-plots after sleeping, but plan to send the boards off to OSH Park Monday (Feb. 10).

The board is 4.0" x 3.9", which makes each one exactly $26 given the $5 per sq. in. price for three boards. I plan on only ordering three unless someone really wants an early board to help with development. If you do, let me know via direct email, or reply to this thread.
Re: RAMPS for BeagleBone
February 10, 2014 04:12PM
Boards are shared on OSH Park. I'm working on the BOM.
Re: RAMPS for BeagleBone
February 11, 2014 12:13AM
Uhh looks good, just what i need. But why only two low-current 12V FET outputs for fans/LEDs?
When can I order?
Re: RAMPS for BeagleBone
February 11, 2014 04:44AM
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Kenzu
Uhh looks good, just what i need. But why only two low-current 12V FET outputs for fans/LEDs?
When can I order?

There are two 12V FET outputs mostly because that's what is on RAMPS-FD, and there's limited current available on the 12V rail when running from 24V. There were zero of these outputs on the original RAMPS, so it's still an upgrade. There are also four buffered 24 mA 5V outputs for the servos that can be used as GPIO, and several other logic-level outputs that can be used to switch things.

As for ordering one, you can order the PCB now from OSH Park. If you want an assembled unit, it will probably be at least a few months, and that assumes someone decides this is worth building and selling. If that doesn't happen I may offer kits, but I'm not sure I can get the cost down sourcing parts for a small run in the US.
Re: RAMPS for BeagleBone
February 11, 2014 05:14AM
Okay, i'am in EU/DK maybe I will build it my self then :-)
How about software? LinuxCNC? or is there any firmware like software that takes gcode and use the PRU's for stepping? I know Replicape has it own software. Maybe I could port that.
Re: RAMPS for BeagleBone
February 11, 2014 05:43AM
I use LinuxCNC running on the BeagleBone. Details are on my blog, along with working SD card images.

Other options I'm aware of include using the Replicape software from Elias, or the BeBoPr software from Bas (although I don't think he's released the PRU code, so it might be hard to move the pins to match this board). It might even be possible to do something really crazy, like port Marlin to the PRU, but I don't think the PRUs have enough program memory for that without major surgury to break out significant chunks of code to run on the ARM.
Re: RAMPS for BeagleBone
February 15, 2014 12:46PM
I would be interested in a kit if you do it even if beta./testing. I'm building a delta and accumulating parts which includes a full RAMPS 1.4 setup which I've been experimenting with various software interfaces(Pronterface, Cura, RepetierHost) driving steppers on the bench. I only have a Hako 928 solder station so some of the surface mount might be tricky although I could call on a friend who's rework employees could easily do it. My plan was for the BBB and Machinekit/LinuxCNC running the 3D delta after getting it up and running with well supported Arduino/RAMPS firmware(Marlin) and users.

Doug
Re: RAMPS for BeagleBone
February 15, 2014 03:51PM
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Dougl
I would be interested in a kit if you do it even if beta./testing.

I won't be selling kits, at least not for a while. I've only got three circuit boards coming back from OSH Park, at a cost of apx. $26 each. Add in the $70+ for a set of parts to put it together and any kit I sell soon will have to cost over $100. You might as well just buy an already put-together BeBoPr.

Once the design is proven, I'll see if I can get someone to build boards, or try to fund enough of a volume purchase the price can come down. This design should be able to sell for well under $50 if there's enough interest to get decent volume (as evidenced by the Geetech folks selling the V1 of the RAMPS-FD for $28). If not, expect to see prices similar to the early RAMPS boards (I bought my kit from Ultimaker for $85 back before the prices came down, and that's probably about what this board would sell for as a kit). Since the BOM will be very close to the RAMPS-FD and has many parts shared with the RAMPS, I'm hoping to be able to get someone who's already building the other RAMPS boards in volume to build some CRAMPS boards as well. That will require interest in the board, so if you want one, post here or otherwise "make some noise" in the usual RepRap hangouts. smiling smiley
Re: RAMPS for BeagleBone
February 15, 2014 03:55PM
I found a couple issues with the BOM, and have made some tweaks so it is easier to deal with going forward. The only real goof was the wrong Molex part number for the motor connectors (I had the 6-pin part number listed, but it's a 4-pin connector). All other changes are mostly cosmetic, although I did add Stackpole part numbers to make ordering from DigiKey easier. The KOA part numbers I had were for Mouser (I had thought the KOA numbers would work for both DigiKey and Mouser, but apparently not).
Re: RAMPS for BeagleBone
February 16, 2014 05:12PM
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cdsteinkuehler
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Dougl
I would be interested in a kit if you do it even if beta./testing.

I won't be selling kits, at least not for a while.

Well, it turns out bobc over in the RAMPS-FD thread is using a PCB vendor with very good prices I had never heard of before. I decided to order 20 boards from them to try out the vendor, which means if they work out OK I'll have some blank boards for anyone seriously intersted.

I also added a PDF copy of the schematic to the github repo. It's available on the CRAMPS RepRap wiki page as well.
Re: RAMPS for BeagleBone
February 20, 2014 08:41AM
I got notices from both OSH Park and the overseas vendor that my boards have shipped, so I'll hopefully be able to build one up next week. The overseas boards are coming standard mail, so might take a couple weeks to arrive. If the design works OK, I should have bare boards available to share for anyone seriously interested.
Re: RAMPS for BeagleBone
February 20, 2014 09:25AM
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cdsteinkuehler
Quote
cdsteinkuehler
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Dougl
I would be interested in a kit if you do it even if beta./testing.

I won't be selling kits, at least not for a while.

Well, it turns out bobc over in the RAMPS-FD thread is using a PCB vendor with very good prices I had never heard of before. I decided to order 20 boards from them to try out the vendor, which means if they work out OK I'll have some blank boards for anyone seriously intersted.

Great! I'll send a ping out to my buddy to see if he'll have someone who could assemble a board. I could also ping a manufacturing company I worked to see if they're interested in the 3D printing biz. Their HQ is based in San Jose and with facilities in China for manufacturing. As you can suspect, things slow down quite a bit but price comes down big time too.
Re: RAMPS for BeagleBone
February 20, 2014 09:38AM
Quote
cdsteinkuehler
Quote
Dougl
I would be interested in a kit if you do it even if beta./testing.

I won't be selling kits, at least not for a while. I've only got three circuit boards coming back from OSH Park, at a cost of apx. $26 each. Add in the $70+ for a set of parts to put it together and any kit I sell soon will have to cost over $100. You might as well just buy an already put-together BeBoPr.

Once the design is proven, I'll see if I can get someone to build boards, or try to fund enough of a volume purchase the price can come down. This design should be able to sell for well under $50 if there's enough interest to get decent volume (as evidenced by the Geetech folks selling the V1 of the RAMPS-FD for $28). If not, expect to see prices similar to the early RAMPS boards (I bought my kit from Ultimaker for $85 back before the prices came down, and that's probably about what this board would sell for as a kit). Since the BOM will be very close to the RAMPS-FD and has many parts shared with the RAMPS, I'm hoping to be able to get someone who's already building the other RAMPS boards in volume to build some CRAMPS boards as well. That will require interest in the board, so if you want one, post here or otherwise "make some noise" in the usual RepRap hangouts. smiling smiley

I was hoping you'd have had enough time to hear from people interested in PCB's so you could have ordered more than just 3 and also brought the price down. But word is still slow about BBB and 3D printing so until more systems start running, i'll probably be bleeding edge costs for a bit more. BTW, the BeBoPr++ is just getting started and while I like the design and it's been proven, it's still an EU product and without giving away private info, it's still pretty costly to us US customers.
Re: RAMPS for BeagleBone
February 20, 2014 10:03AM
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Dougl
I was hoping you'd have had enough time to hear from people interested in PCB's so you could have ordered more than just 3 and also brought the price down.

I haven't heard from many folks, but I did order 20 boards from overseas as an experiment (with shipping cost was actually less than 3 boards from OSH Park!). Quite a savings, and I'll have boards available if the design checks out OK once I get one built (hopefully next week).

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Dougl
BTW, the BeBoPr++ is just getting started and while I like the design and it's been proven, it's still an EU product and without giving away private info, it's still pretty costly to us US customers.

Yes, I like both the BeBoPr and the Replicape designs, but the cost is pretty high. Volume would help bring costs down, but both boards are dramatically more complex than the proven RAMPS design, and complexity is expensive.
Re: RAMPS for BeagleBone
February 20, 2014 04:03PM
Hmm, I'm curious to hear what you have to say about EU products... Please share your thoughts with us.

-- Bas
Re: RAMPS for BeagleBone
February 20, 2014 04:27PM
Charles,

I'm cranking op volume and the price has gone down from EUR 117 for the BeBoPr+ to EUR 84 already for a single BeBoPr++. When buying three boards the price is EUR 74 each. These boards include an accurate ADC to replace the crap version on the BeagleBone.

Your BOM does not include prices so it's hard to make a fair comparison and people here seem to focus on PCB cost only.

What complexity do you mean exactly? I see original BeBoPr features being integrated in the latest RAMPS designs (E.g. mergency stop and analog input protection), so RAMPS seems to be getting more complex with each new design.

-- Bas
Re: RAMPS for BeagleBone
February 20, 2014 05:51PM
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modmaker
I'm cranking op volume and the price has gone down from EUR 117 for the BeBoPr+ to EUR 84 already for a single BeBoPr++. When buying three boards the price is EUR 74 each. These boards include an accurate ADC to replace the crap version on the BeagleBone.

Great news, and those are great prices! Keep us all updated on the options for purchase, and I'll get my blog cape page updated if you send me details. Do you have any plans for a US distributor?

Quote
modmaker
Your BOM does not include prices so it's hard to make a fair comparison and people here seem to focus on PCB cost only.

My cost for one board right now is about $100 US, but that's parts only, qty 1, buying parts for one board from DigiKey ($70) with PCB from OSH Park ($26 ea), and probalby another $5-$15 in parts that I got sampled or have on-hand (the stack-through connectors and a couple TI parts). As I mentioned to someone else, at this point buying a pre-built BeBoPr is still the best way to go (and could easily continue to be). If I was selling boards (and I don't plan to), I likely wouldn't be able to match your 117 EU for assembled units, much less the 84 EU price of the ++, certainly not without getting into buying lots for 50-100 boards at a time...and I don't want to get into the board business. I honestly did this design as much to test out KiCAD (it's workable, but _painful_ to use for production designs in it's current state) and run some larger boards through OSH Park and some off-shore vendors as anything else.

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modmaker
What complexity do you mean exactly? I see original BeBoPr features being integrated in the latest RAMPS designs (E.g. mergency stop and analog input protection), so RAMPS seems to be getting more complex with each new design.

Yes, the CRAMPS (and the RAMPS-FD it's based on) are more compelx than the inital RAMPS board (which was mostly just a PCB with various connectors), but it is still simpler in design than the BeBoPr or Replicape. Specifically, I'm referring to things like:

5V power: This is provided by the BeBoPr/Replicape, but the CRAMPS requires you provide 5V to the BeagleBone or populate a header with an optional 5V regulator module.

FET Drive: The CRAMPS/RAMPS-FD uses the same logic-level FETs with 5V drive as used on the RAMPS. I've never much cared for this solution and it means more expensive FETs and larger packages to dissipate the resulting heat from not using a 10-12V gate drive. But the RAMPS-FD folks didn't like my "poor-man's" FET drive suggestions, and I'm sticking with the 74ACT drivers they settled on. They are readily available and inexpensive, the only drawback is the 5V gate drive. :-/

I/O Protection: The CRAMPS does what I would classify as minimal protection. It should be possible to hook 5V signals up to some pins, but overal it will be much easier to fry your BeagleBone using a CRAMPS board than a BeBoPr.

ADC: As you mentioned, the on-chip ADC on the BeagleBone "lacks performance" smiling smiley The CRAMPS design uses the on-chip ADC (and inherits all the noise and other problems that brings with it), and has what I would define as minimal input protection. I'd feel much better with op-amps in the circuit, but those cost money and aren't on the RAMPS-FD BOM (another goal is to try and get some RAMPS/RAMPS-FD vendors to build the CRAMPS too, so having a very similar parts BOM is important...I don't want to get in the building boards business).

Overall, I see room for a spectrum of products. There are several low-cost CNC capes available, I did the CRAMPS board because I'm hoping it can fill this segment for the 3D printer folks. The next step up would be a board like the BeBoPr++ or Replicape, followed by something like an FPGA daughtercard (none are currently available, but a few designs are in the works). Note that my perspective is focused on using LinuxCNC as the control software. I know you have your software, and Elias has something he's using with the Replicape (I honestly have yet to test out either...I should do that sometime!). Choice of software can dramtically affect the decision of hardware to buy...for instance the BeBoPr is the *ONLY* board currently supported by LinuxCNC. Even my CRAMPS design doesn't have any working example configurations yet, and it will probably be some time until the Replicape is supported, since it requires use of various hardware interfaces (I2C and SPI controllers) I haven't written LinuxCNC HAL drivers for yet.
Re: RAMPS for BeagleBone
February 21, 2014 03:16AM
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cdsteinkuehler
Quote
modmaker
I'm cranking op volume and the price has gone down from EUR 117 for the BeBoPr+ to EUR 84 already for a single BeBoPr++. When buying three boards the price is EUR 74 each. These boards include an accurate ADC to replace the crap version on the BeagleBone.

Great news, and those are great prices! Keep us all updated on the options for purchase, and I'll get my blog cape page updated if you send me details. Do you have any plans for a US distributor?

I'll start making announcements soon, first build up some stock. I don't want to sell vapour-ware.

No distributors yet. I intend to facilitate group buys via the BeBoPr forum. This way the shipping costs can be split and the best price can be reached. Anyone willing to take some stock is welcome though.

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cdsteinkuehler
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modmaker
Your BOM does not include prices so it's hard to make a fair comparison and people here seem to focus on PCB cost only.

My cost for one board right now is about $100 US, but that's parts only, qty 1, buying parts for one board from DigiKey ($70) with PCB from OSH Park ($26 ea), and probalby another $5-$15 in parts that I got sampled or have on-hand (the stack-through connectors and a couple TI parts). As I mentioned to someone else, at this point buying a pre-built BeBoPr is still the best way to go (and could easily continue to be). If I was selling boards (and I don't plan to), I likely wouldn't be able to match your 117 EU for assembled units, much less the 84 EU price of the ++, certainly not without getting into buying lots for 50-100 boards at a time...and I don't want to get into the board business. I honestly did this design as much to test out KiCAD (it's workable, but _painful_ to use for production designs in it's current state) and run some larger boards through OSH Park and some off-shore vendors as anything else.

Quote
modmaker
What complexity do you mean exactly? I see original BeBoPr features being integrated in the latest RAMPS designs (E.g. mergency stop and analog input protection), so RAMPS seems to be getting more complex with each new design.

Yes, the CRAMPS (and the RAMPS-FD it's based on) are more compelx than the inital RAMPS board (which was mostly just a PCB with various connectors), but it is still simpler in design than the BeBoPr or Replicape. Specifically, I'm referring to things like:

5V power: This is provided by the BeBoPr/Replicape, but the CRAMPS requires you provide 5V to the BeagleBone or populate a header with an optional 5V regulator module.

I think it's part of the charm of the BeBoPr that you need only one supply. And now that you can use anything between 12 and 24 Volts it's even more attractive. The original Replicape did not have this feature and it was added later, so I'm not the only one seeing the benefits. But I agree that it's probably 'too complicated' for the average RAMPS design(er).

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cdsteinkuehler
FET Drive: The CRAMPS/RAMPS-FD uses the same logic-level FETs with 5V drive as used on the RAMPS. I've never much cared for this solution and it means more expensive FETs and larger packages to dissipate the resulting heat from not using a 10-12V gate drive. But the RAMPS-FD folks didn't like my "poor-man's" FET drive suggestions, and I'm sticking with the 74ACT drivers they settled on. They are readily available and inexpensive, the only drawback is the 5V gate drive. :-/

Initially I thought that the cheap logic level design would suffice too. But heat could cause a problem in situations where people were not careful enough. That's why I re-designed the PWM output stages. The BeBoPr++ is now capable of directly switching a 10A load (e.g. a HBP) higher without burning the FETs from the board. The thermal picture below shows the BeBoPr++ switching 10A at 40 kHz (98% duty cycle). At this frequency the temperature rise of the FETs is around 22 degrees C above ambient, of which 5-6 degrees is caused by switching losses. The fuse is by far the hottest component in the area, but that one is meant to self destruct hot smiley



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cdsteinkuehler
I/O Protection: The CRAMPS does what I would classify as minimal protection. It should be possible to hook 5V signals up to some pins, but overal it will be much easier to fry your BeagleBone using a CRAMPS board than a BeBoPr.

Frying the BeagleBone is less of an issue since the BBB. It's so dirt cheap, at least if you can get one angry smiley

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cdsteinkuehler
ADC: As you mentioned, the on-chip ADC on the BeagleBone "lacks performance" smiling smiley The CRAMPS design uses the on-chip ADC (and inherits all the noise and other problems that brings with it), and has what I would define as minimal input protection. I'd feel much better with op-amps in the circuit, but those cost money and aren't on the RAMPS-FD BOM (another goal is to try and get some RAMPS/RAMPS-FD vendors to build the CRAMPS too, so having a very similar parts BOM is important...I don't want to get in the building boards business).

I've been testing and packing a batch of BeBoPr++ boards now. Is a pleasure to see these ADC values after all the troubles with the BeagleBone's ADC. I'm now getting stable and reproducable measurements on all the boards. Not even a single bit of noise. The BeagleBone's ADC is now free to use for a touch-screen, as was probably intended. I think TI can do a better job and fix the driver, but maybe they have a silicon problem and this will be all we get. Most micro-controllers ADCs perform much better.

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cdsteinkuehler
Overall, I see room for a spectrum of products. There are several low-cost CNC capes available, I did the CRAMPS board because I'm hoping it can fill this segment for the 3D printer folks. The next step up would be a board like the BeBoPr++ or Replicape, followed by something like an FPGA daughtercard (none are currently available, but a few designs are in the works). Note that my perspective is focused on using LinuxCNC as the control software. I know you have your software, and Elias has something he's using with the Replicape (I honestly have yet to test out either...I should do that sometime!). Choice of software can dramtically affect the decision of hardware to buy...for instance the BeBoPr is the *ONLY* board currently supported by LinuxCNC. Even my CRAMPS design doesn't have any working example configurations yet, and it will probably be some time until the Replicape is supported, since it requires use of various hardware interfaces (I2C and SPI controllers) I haven't written LinuxCNC HAL drivers for yet.

Re: RAMPS for BeagleBone
February 21, 2014 07:51PM
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modmaker
Hmm, I'm curious to hear what you have to say about EU products... Please share your thoughts with us.

-- Bas

oops, I didn't mean it the way it might have been taken. I know Charles is also in the USA so the comment about it being an "EU product" was 100% related to cost and how long it would take to get production up for USA purchasers. I recall even sympathizing with you all over there when I posted, having read many times about this or that USA product being tough and/or expensive to get over the pond. I'm sorry that I may have stirred your emotions a bit with the previous statement.

Doug
Re: RAMPS for BeagleBone
February 24, 2014 09:18AM
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Dougl
Quote
modmaker
Hmm, I'm curious to hear what you have to say about EU products... Please share your thoughts with us.

-- Bas

oops, I didn't mean it the way it might have been taken. I know Charles is also in the USA so the comment about it being an "EU product" was 100% related to cost and how long it would take to get production up for USA purchasers. I recall even sympathizing with you all over there when I posted, having read many times about this or that USA product being tough and/or expensive to get over the pond. I'm sorry that I may have stirred your emotions a bit with the previous statement.

Doug

Hi Doug,

Let's say you hit a raw nerve winking smiley Your words "pretty costly" and "still an EU product" did sound rather biased. But I'm glad it was a misunderstanding.

Regrettably I'm only an engineer and I can't change geography and related shipping costs (in neither direction). I do think the BeBoPr++ is a high quality product at a very attractive price. By cooperating it should be possible to beat the system and find a way to lower shipping costs. Last week I've shipped several packages to the US. A couple of these boards will be available for resale in the US and hopefully more will follow.

As Charles implies in his reaction, building a CRAMPS is probably going to be "as pretty costly" as buying a BeBoPr. Of course, if you take pleasure from building a board yourself you should do so. I probably would. But in that case I probably wouldn't get a realistic cost comparison. Spending (too) many hours to save a little cash and having lots of 'free' parts already available. Comparing costs for that situation is like comparing apples and oranges.

So please don't judge based on gut feelings or hear say, and next time present us with a realistic and complete calculation smiling smiley

Cheers,
-- Bas
Re: RAMPS for BeagleBone
February 24, 2014 02:45PM
US price probably does not include vat because they dont have that. EU price probably includes it, most probably all components have that included in purchase price. So the eu price is comparable if you keep track of vat. If one would want to import large quantities or merchandise from us to eu, would have to pay vat at customs, the vat in the country where the import is made. Sort of speaking, can not avoid eu vat indefinatelly nor completely.
Re: RAMPS for BeagleBone
February 25, 2014 03:02AM
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NoobMan
US price probably does not include vat because they dont have that. EU price probably includes it, most probably all components have that included in purchase price. So the eu price is comparable if you keep track of vat. If one would want to import large quantities or merchandise from us to eu, would have to pay vat at customs, the vat in the country where the import is made. Sort of speaking, can not avoid eu vat indefinatelly nor completely.

The rules are a bit more complex. Short and simplified form: Individuals (not coorporations) in the EU will be charged 21% VAT on products from the Netherlands. Anyone from outside of the EU pays 0% VAT. VAT stands for Value Added Tax. The VAT being charged over goods you buy is calculated over the price excluding the VAT that was charged when acquiring these goods (you might have to read this sentence twice). Plus you pay VAT over the 'value' that was 'added' to the original goods. So if everything is handled properly, you never pay double VAT, but once for each amount of value that gets added.

If you're an individual living in the EU (and thus have bought components including VAT) to create a product that's being sold outside the EU you have a disadvantage. In that case your product will probably be too expensive because it includes some VAT while none should have been. The disadvantage depends on the (relative) amount of value you've added. If you make 90% profit on some merchandise you bought with VAT included, the disadvantige is relatively small. However if you paid VAT over 50% of your parts, the disadvantage is significant!

-- Bas
Re: RAMPS for BeagleBone
February 25, 2014 03:52AM
If you want to make exports as individual you would be at disadvantage idd. But, you could make a small company for that purpose and that means when you export goods, you get back the vat you paid, and that would be probably worth it.
Re: RAMPS for BeagleBone
February 27, 2014 06:35AM
As painful as the PCB layout was to do in KiCAD, it pales next to the frustration caused when trying to extract decent manufacturing data from the package. Much of this is not the fault of KiCAD itself (it's how the library parts were setup and used), but KiCAD isn't making it any easier to deal with.

Anyway, I've updated the ToDo list on github with issues I noticed while assembling the first board. I have also imported the design into circuithub. It will be interesting to see what they come back with for an assembled cost.

I've put some pictures of the assembled board on G+ if you want to see what the boards look like.
Re: RAMPS for BeagleBone
March 01, 2014 07:19PM
The design is so far working mostly as expected. I'm posting updates to the reprap wiki page, and will try to get a video uploaded soon.

The only thing not really working as expected is the thermistor inputs. The signal levels are so low at room temperature with a 1.8V ADC range that the leakage from the protection diodes is causing measurement offsets. I am considering simply removing the protection diodes from the next version (I have already removed them from my prototype), as I'm not sure they really help all that much. The right way to protect the inptus is with a high input impedence insturmentation amplifier, but that costs money and adds complexity. The design still has a 4.7K series resistor to help protect the analog inputs, which probably puts the BeagleBone about even with the Arduino Mega used with the original RAMPS (which had absolutely *NO* analog input protection at all, but the AVR is likely a bit more robust than the AM3358 on the 'Bone).

If you have any strong opinions about keeping or removing the analog input protection, let me know.
Re: RAMPS for BeagleBone
March 25, 2014 07:57PM
Assembly instructions and ECOs are being added to the new RepRap Wiki CRAMPS V1.0 page, if you're building a board of your own. I also have several blank PCBs available, contact me direct if you would like one.
Re: RAMPS for BeagleBone
May 07, 2014 04:48AM
Files for V2.0 have been uploaded to github, and sent out for PCB fabrication. I'll get the RepRap.org wiki pages updated soon.
Re: RAMPS for BeagleBone
July 21, 2014 07:24PM
Quote
cdsteinkuehler
The only thing not really working as expected is the thermistor inputs. The signal levels are so low at room temperature with a 1.8V ADC range that the leakage from the protection diodes is causing measurement offsets. I am considering simply removing the protection diodes from the next version (I have already removed them from my prototype), as I'm not sure they really help all that much. The right way to protect the inptus is with a high input impedence insturmentation amplifier, but that costs money and adds complexity. The design still has a 4.7K series resistor to help protect the analog inputs, which probably puts the BeagleBone about even with the Arduino Mega used with the original RAMPS (which had absolutely *NO* analog input protection at all, but the AVR is likely a bit more robust than the AM3358 on the 'Bone).

If you have any strong opinions about keeping or removing the analog input protection, let me know.

What have you done with this in the newer versions of the board? Particularly, I see that a fully assembled v2.2 board is available from pico-systems. What is the state of the thermistor readings at room temperature with this version?
Re: RAMPS for BeagleBone
July 22, 2014 02:20PM
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kroylar
What have you done with this in the newer versions of the board? Particularly, I see that a fully assembled v2.2 board is available from pico-systems. What is the state of the thermistor readings at room temperature with this version?

I changed the pull-up resistor for the thermistors from 1K to 2K and I removed the diode clamp circuitry. The thermistors are working fine, and are mostly limited by the on-board ADC performance of the BeagleBone. Adding software filtering helps quite a bit.
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