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Is the new Arduino Due compatible with RAMPS 1.4?

Posted by Wraithnot 
Is the new Arduino Due compatible with RAMPS 1.4?
October 21, 2012 03:00PM
According to an article in wired, the Arduino Due goes on sale tomorrow for $49.

"The long-awaited Arduino Due just hit the market, replacing the 8-bit, 16MHz brain of the popular Uno microcontroller prototyping platform with a 32-bit, 84MHz processor, while augmenting inputs and capabilities all around."

And an article in hackaday says:

"The board looks strikingly similar to the already common Arduino Mega. That’s no mistake; the DUE is compatible with existing shields, so connecting a RAMPS board for your 3D printer should be a snap."

So it sounds like there is a good chance it will be compatible. The logic voltage changed to 3.3V from 5V, but my amateur's reading of the Pololu stepper driver specs indicates that should still work. But will the voltage change screw up some other aspect of interfacing with RAMPS? Will standard firmware still work with the Arduino Due? Will it really be as simple as swapping out the Arduino Mega for an Arduino Due?
Re: Is the new Arduino Due compatible with RAMPS 1.4?
October 21, 2012 04:21PM
I know Josef Prusa has one, but I have no idea if he's tried it yet.

FWIW: The only issues I can think of are:
Thermistors (maybe different tables, or have some sort of scaling mechanism?)
Pololus (which would be fine)
Input voltage (can the Due adequately dissipate that heat with a shield like RAMPS sitting on top of it)

IMO none of these should be show-stoppers.

Note: Things like the SD card add-on, thermocouple drivers and LCD boards may require some changes, as at least many of the LCD setups use 5V (though most can use 3.3V). You'd want to check that each of those will work fine with a 3.3V setup.
Re: Is the new Arduino Due compatible with RAMPS 1.4?
October 22, 2012 12:57AM
The thermistors and endstops would need to be run at 3.3V, to avoid sending an out-of-range signal back to the Due; probably the easiest way to do this would be to replace the RAMPS 5V supply by 3.3V throughout.

The heater control MOSFETs may also require changes, as too low a control voltage will only partly turn them on, causing them to overheat.

Firmware that only used the Arduino libraries would work, but I don't know whether this exists; firmware that directly uses AVR features won't work.
Re: Is the new Arduino Due compatible with RAMPS 1.4?
October 22, 2012 02:40AM
You're on the right track, rebecca.palmer. At least the MOSFETs need replacement.


Generation 7 Electronics Electrochemical Machining RepRap DIY
Teacup FirmwarePCB Milling
Re: Is the new Arduino Due compatible with RAMPS 1.4?
October 29, 2012 05:22AM
I can see many MOSFET choices for low RDSon at Vgs=2.5V that may work: [ec.irf.com] but most are SMD.
Re: Is the new Arduino Due compatible with RAMPS 1.4?
October 29, 2012 09:24PM
The FDP8860's also have a low Vgs (2V from memory) so they should be fine too.
Re: Is the new Arduino Due compatible with RAMPS 1.4?
December 06, 2012 03:06PM
Greetings all,

From the schematic http://www.reprap.org/mediawiki/images/3/3f/Arduinomegapololushieldschematic.png
The MOSFETs for the three heater/fan channels are part# STP55NF06L whose datasheet is available online at [datasheet.octopart.com]

Figures 3 and 4 give the most relevant data. Figure 3 indicates that with Vgs = 2.5 volts, the Max current (drain to source) is just above 15 Amps. (2.5 volts is conservative, but we cannot guarantee 3 volts from an I/O pin driven by logic with a 3.3 volt supply.)

Since the X axis of Fig 3 is in volts and the vertical axis is in Amps, the initial slope of the 2.5 Vgs curve is its resistance in ohms. By eyeball, that appears to be on the close order of 3 volts / 30 Amps, thus an effective resistance R_ds of 0.1 Ohms. On one hand, this is large compared to the effective resistance if the gate were to be driven to a full five volts (or even a diode drop below.) However, what we really care about is (1) how much voltage drop does the MOSFET "steal" from whatever it's driving and (2) how much power is dissipated in the MOSFET (namely, will it get too hot.) From the R_thj_a value of 62.5 deg. C / Watt (and ambient temp @25 and max junct temp of 150 {conservative, the datasheet says it can handle up to 175 deg. C}), we have P_max_noHeatSink = (150 -25)/62.5 = 2 Watts max. Now P = i^2 R. From this, i_max is sqrt(20) == 4.47 Amps. That's plenty for fans, but not enough for max power through a nominal PCB heated bed (0.8 ohms, which would draw 15 Amps from 12 volts.) A heated bed with a higher resistance, namely 3 ohms (12 volts / 4 Amps) and up ought to work with the original MOSFET.

I know I found at least one MOSFET with a nice low Vgs, suitable for 3.3V logic. Now I have to search for it again. If I find it, I'll post the part#.
Re: Is the new Arduino Due compatible with RAMPS 1.4?
December 06, 2012 04:00PM
I think the Pololus will have the wrong logic threshold unless you power them from 3.3V rather than 5.


[www.hydraraptor.blogspot.com]
Re: Is the new Arduino Due compatible with RAMPS 1.4?
December 06, 2012 05:47PM
I got this from the Pololu website about the A4988:

"The driver requires a logic supply voltage (3 – 5.5 V) to be connected across the VDD and GND pins..."

Does that mean it will work on a 3.3V system, or does that mean it just needs 3V to run, and still needs the 5V for a signal? Either way, it explicitly says on the DRV8825 page that they work on 3.3V or 5V logic.
Re: Is the new Arduino Due compatible with RAMPS 1.4?
December 06, 2012 05:58PM
Oh, just looked up the pins on the Due and the RAMPS layout, and I see what you're saying nophead; it looks like all the VDDs are connected to a 5V pin that's still 5V on the Due. I had assumed they were connected to IOREF.
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