I finished up the first beta of my Espressylu, a low cost 32bit reprap control board. The goal is to make a safe and reliable board that sets a new standard for the low cost market.
This board is based off of the Teensylu board, with some major upgrades.
Most notable changes are:
Atmel SAM3x 32bit mcu
Smd mosfets
Onboard microsd
Mosfet drivers
Mini fuse
24v operation
The board is designed for 24v operation only. It’s possible to run 12v with some alterations to the bom, but would require 2oz copper layers. I am trying to push for 24v, it’s much safer.
I’m currently looking for people to do schematic and layout review. As a bonus, if you provide useful feedback (at my discretion), I will donate to contributors an unpopulated board once it’s built. (may take some time before I have them built). I can also populate the boards at-cost + shipping to the US.
Good work! I would love to see a low cost PCB with wired ethernet (like a low cost Duet or Smoothieboard) or even wireless network - I think that’s the next step. The key is being able to use an established existing open-source compatible firmware.
@Stephanie_A
Routing is great. I see you put traces on several different layers, but I don’t see any indication that this is more than a 2 layer board.
Looks like the dimensions are very close to the max that eagle freeware permits. Do you need to go larger? I have eagle pro if you want me to do anything that requires it.
Are you comfortable with your choice to go down to 0402 size passives? Even if you can solder them, do you expect that an average user making one for themselves will be able to? I’m able to solder 0805s and 0603s with a fine tipped soldering iron, but 0805s are much more comfortable to do. If you have solder paste, a stencil, and a reflow (aka toaster) oven you could place 0402s by hand, but I don’t imagine it would be very pleasant to do, and I wouldn’t expect someone trying to build a one off to purchase a stencil, even if one of OSHStencils is only in the $10-20 range.
I sent you an invite in hangouts if you’d like to chat further.
I used Eagle. The firmware is TBD, but it is arduino compatible, so any firmware that works on arduino should be able to work.
The MCU is essentially a feature limited version of the Arduino Due. I specifically choose this board because it does not have Ethernet, and the pin cound matches my needs. It should be easy to add wifi. It’s also possible to modify the USB so it’s USB-OTG compatible, which means you can add usb host support. I haven’t done that because of limitations.
You can view boards that use the DUE here: http://reprap.org/wiki/Arduino_Due_Based_Electronics any firmware that works for these should work for this board if Ethernet is disabled.
@raykholo It’s a 4 layer board. I don’t know if it will render correctly or not. I didn’t use 0603 components, which I would prefer, because I was worried about space and had a lot of trouble laying out the traces. I solder boards for a living, so I have no problem doing 0402 components. The device is better suited for mass manufacturing anyways.The SAM3x is a sensitive device, so it requires a lot of filters. I tried to place the decoupling capacitors as close to the device as possible. I don’t have the full version of eagle, so it took a lot of work and beers for friends to make the board 4 layers.
The board size is exactly the limitations of the free version, and I’m ok with that, I don’t want it to be any bigger, so the size constraint is a good thing.
Can’t look into things, cause I’m on mobile… What are the stepper drivers? Onboard or pololu-sockets? How many drivers? What are the dimensions? 24V is great (all my printers are on 24V) but if it’s meant to be a small board, 19V would be better, because of cheaper PSU.
Can someone provide more info for mobile users?
They plug into the Ramps board. You will have one per stepper motor (unless you have 2 plugged into tge Z driver) and maybe a spare. There are spots to plug in 6.
This board supports 4 stepper drivers, 2 heaters, and an expansion header. It uses polulu sockets. I can change it to support 19v, the main VR has an UVLO set to trigger at 20v, a resistor change is all thats needed.
The connectors and mosfets are all spec’d for 12v operation. A manufacturer can remove the UVLO and build the board on 2oz copper and it would work perfectly fine with 12v.
The dimensions are 4in by 3in, the maximum allowed by the free version of Eagle.
I like your heater MOSFET approach, big honking FETs sticking straight up with inadequate gate drive voltage always bugged me. I don’t know much about those FET drivers, is there any new PWM frequency limit or anything to worry about with them?
Is there a way to hook up XYZmax endstops and a Zmin probe for deltas? Maybe pin re-assignment on the E-stop or something?
I see a transistor on the Z stop circuit, I’m guessing that’s a cutoff for inductive probes or something like that… what’s the objective? Will there be issues if people want to use other endstop switches that may require active high or active low logic?
Cut trace / solder blob microstep select jumpers aren’t my favorite (eg painful if you’re trying different configs), but I guess proper jumpers are a fair bit of real estate.
I think the driver enables should be all pulled low, not high…?
Do you have the thermistors routed and grounded for noise avoidance? I’m a rank amateur with this stuff, but running therm between the X stepper and hot end heater seems non-optimal. Noise in the thermistor ADCs has been a big issue for a lot of boards in the past, eg look at the ground plane changes between the Duet 0.6 and 0.8.5 revs, it makes a huge difference in temp sensing stability. The Smoothieboard r1 MCU has well-known ADC noise issues which they had to take care of via extensive filtering/oversampling in firmware. Lots of other examples out there.
The FET Drivers should handle high freq, in all they will drive much better than what the MCU can do as they can sink/source waaay faster. (I think it was up to 2 amps).
On my first build I will probably omit the drivers and the VR to power them, just to see if those fets and the mcu can withstand a 3.3v gate drive.
it would be easy to reconfigure whatever firmware you use for the endstops. Just because they’re labeled as X,Y,Z,E doesn’t mean that you need to use them as such.
The pre-biased transistor on the Z stop is a copy job from the Printrboard. it’s a cheap trick for level translation. all you need is the pullup enabled on the pin. invert/etc still works like normal. It should handle 24v… I think (totally need to test it).
The Z endstop supplies both 24v and 3.3v, this allows you to design whatever board you need for level translation of a Z probe.
I agree that a solder blob isn’t the best way, I tried to design it so that it would work well. I could switch to micro pin headers, but those mini jumpers are hard to come by. I’ll take another look at the board and see what I can do. not much space there, I could do SMT jumpers, but those always break.
The ADC has a bunch of filtering, so at least it should be stable in sampling, but I can’t say the same for noise picked up on the ADC pins. There is a filter in the form of 10uF caps across the pins. I don’t know if that is the best choice for HF noise. I could add those ferrite beads to the GND side, which should eliminate all noise. Ideally the GND would be from the ADC GND plane, but that’s just not possible. the noise on the 12v plane would cause the most issues. I could put small caps around there to clean it up, or maybe a cap on the heater pins. I have no idea if it would work, or how to properly add them.
you could place 0402s by hand, but I don’t imagine it would be very pleasant to do, and I wouldn’t expect someone trying to build a one off to purchase a stencil, even if one of OSHStencils is only in the $10-20 range.