dzach wrote:This sounds really interesting at that price. I'd like to see the LCD interface included as well as the ATX connector, although this might mean the 160x80 size will become unavoidable.
Some questions:
- Are the SD card and (optional) LCD display going to be supported by the software?
- Does the software support the new current limiting capabilities of the A3988 driver?
- Is the PCB going to be a 3layer one? Alegro MicroSystem recommends it as a low point ground and thermal path.
- The chip manufacturer gives a 1.2A per phase current rating, i.e. 2.4A per axis. How is the 3A max achieved?
Considering the combined heated bed + ORDuino PCB, could that be a kit with all SMT parts (including the ones for the heated bed) pre-soldered and all the non SMT parts supplied with the uncut PCB?
That would make it an unbeatable offer (at present at least)for the ORDuino + heated bed!
Cool, thanks for the great feedback!
My understanding is the SD card is already supported in the current popular Arduino firmware that supports RAMPS, as the "SDramps" add-on card is pretty popular. It uses the SPI interface, which will also be used to control the LCD and motor driver settings, so some small additions to the code will be necessary to multiplex all 3 on the same spi port. this is a fairly trivial programming exercise though.
I'm not planning to use the A3988 or any other part from Allegro. I was lookign for another IC, and i briefly considered the a3982 (almost identical, slightly different package) because you cant find any for sale, they are deeply backlogged due to popular demand, and now the 3982's are pure unobtaineum as well. there's plenty of 3983's (same but 1/8 microstepping only) at Digikey at the moment but that could change at a moment's notice.
In the end i found and chose a part that is vastly superior in almost every way except price. - its slightly more expensive, but worth it- its a new part just being released but i have parts and the factory tells me they have over 122,000 of these parts available - not likely to run out any time soon. its one of the top 10 US semiconductor companies and they have really excellent support & documentation, i would put them as #1 in that respect.
The PCB is 2-layer only to save cost, that's why it is physically larger and more spread-out, but will have 2Oz or 3Oz copper. There's no such thing as a 3-layer board- the next step up is 4-layer, then 6, etc. they're done in pairs to prevent board warp, and the process just works out better that way- 3-layers would be more expensive than 4 and cause issues as a result.
I make my living designing boards and i'm an expert / consultant with Altium so i can promise the layout will be top notch and really well engineered from an thermal, EMI, susceptibilty, and assembly point of view. If you're interested i can tell you its really 2-1/2 layers in the digital section - most of the signals route on the top layer, so the bottom side is mostly solid ground plane with carefully controlled perforations to bridge signals on top or small power islands. I routinely do mixed-signal analog /digital / power / RF designs (to 2.4G) this way and have never been disappointed with the results. But i'm not afraid to do a 6- or more layer board when necessary
Bottom line is, you can do a lot with good board layout and thermal considerations, but the best approach is to just not generate the heat in the first place - so: very low-RDS-on mosfets, small or no current sense resistors, switching vs linear regulators, etc. Which is that i've done first with this design. Result is less than 1/2 the power dissipation to begin with vs stock ramps+ pololus
Thats an interesting idea to sell it as kit with through-hole parts unmounted.
i'll consider doing that for the initial run but not sure what if any savings it may produce ,because only a few of the optional connectors are actually through hole, everything else is SMT - my thought was to have a "vanilla" version with only SMT / basic connectors, and a couple of other SKU's with optional TH connectors like ATX, DIN, Mini-Fit, or some TH Faston tabs (they take much less board space).