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Using SPI only for stepper control

Posted by NforcerOH 
Using SPI only for stepper control
December 11, 2017 12:21PM
First off I'm not a control board designer but I'm thinking about a system, could we use more compact boards with less pins by using SPI/I2C to control steppers and read the inputs needed? It seems that if you remove the pin limitation on the atmega or the Due by taking advantage of the SPI/I2C buses you can control more sensors/devices. Why not use some ADS1115 for reading the temps and some CD74HC4067 or the likes to controller the stepper drivers. With the TMC2130 that support SPI, seems it's feasible. and allows for more steppers that a FDM printer would need for now.
Re: Using SPI only for stepper control
December 11, 2017 12:50PM
... check first the timing limits - how fast can you aquire sensor data and (synchronized) control steppers with SPI/I2C?

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Re: Using SPI only for stepper control
December 11, 2017 06:11PM
SPI interfaces are too slow to send individual step commands to stepper drivers at the speeds needed in 3D printers. You would need to use a more intelligent stepper driver that can do complete moves by itself - preferably including segmentation-free delta printer moves - and you would need an common clock signal to synchronise them.

I2C is rather limited because of its high latency, but OK for some things such as temperature control.

In fact the SAM3X processor used in the Arduino Due has quite a lot of extra I/O pins that are not made available on the Due. So all-in-one controller boards are less constrained by I/O than controllers based on Arduinos.

Btw the ATSAM3X8E processor used on the Arduino Due is heading towards obsolescence, just like the atmega2560. Price wise, the sweet spot right now in the Atmel/Microchip range of high pin count microcontrollers is ARM Cortex M4 and M4F processors.

Edited 2 time(s). Last edit at 12/11/2017 06:12PM by dc42.

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Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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