EinW Cronos 3-axis grbl controller ebay add photo

Arduino based CNC controller for separate stepper drivers?

It is the result of an amazing open source project, and once again I am grateful to those who put the time and expertise into such endeavors.

My small CNC mill project needs motors (so I’m told) that are too powerful for the regular drivers included with the grbl Arduino shields (or the equivalents of the built in Arduino + drivers), and so I’ve been thinking of designing my own to hook up to external motors.

The (default) brief was to keep it as simple as possible while providing proper ground loop impedance ground loop hardware interfaces for everything grbl can do.

Which means:

  • There are no microcontroller pins directly connected to the outside world
    = stored input
    = stored output
  • EMC and ground loop protection on the input
  • Inputs for final stop and routing switches
  • Inputs for pause, stop and continue
  • Support for normally closed key inputs – by far the safest option used on professional CNC machines.
  • No more external 0.1 inch header connections – just the right connectors
  • Power from the motor supply rail is ~36V
  • USB is isolated if there must be a USB
  • Connection for “off-line controller” (see below) if there is no USB
  • Enclosure able – so no heat required fan

Opto isolators on all inputs will go a long way to solving EMC input and ground loops.

This is even an official GitHub / gnea / grbl isolation circuit for the folks to add to the typical grbl commercial panels

With grbl, both boundary switches of either axle are connected to the same input (hence only three options), and a serial connection is the only sensible connection as it is most likely to be fail-safe.

In any case..

3-axis grbl controller EinW Cronos add imageImagine my delight when I discovered this almost exactly, from Chinese parts supplier Cronos via ebay (photo ebay truly) – The ad said the processor was 32-bit (see below) but I was pretty sure it was a standard board based on a low-hassle 8-bit processor.

Unable to do my due diligence, I just paid the money, and now it’s arrived and it already looks like it’s 8-bit – I haven’t turned it on yet, but the processor is marked 328P.

Even better, it came in a DIN rail mounted enclosure and everything looked “fit” rather than a bargain basement.

3-axis grbl controller EinW Cronos add imageJust looking around, board inputs (Image eBay the left) are optically isolated, and the off-board buffers appear to be HC245s I’ve seen used elsewhere – they’re not really linear drivers, but they’re much better than asking the ATmega to drive off the board. There are also some opto-isolators near the outputs – I’m not sure where they fit into the equation yet.
BTW, the inputs to the associated motor drivers are optically isolated, so grounds will not be modulated with the HC245’s outputs.

32bit disappointment?

The joy was tempered slightly by disappointment that the board wasn’t 32-bit, as this would have given it the ability to cut the original g-code curves, for example, due to the much higher processing power of 32-bit processors with their associated higher clock speeds.

But it wasn’t a huge disappointment – I don’t want this to turn into a software project, and 32bit grbl is more or less like that at the moment, while 8bit grbl 1.1 has been stable for over a year only requiring basic Arduino skills.

FYI, at least two projects: grblHAL And the grbl_esp32I took what was an 8-bit grbl project and extended it to 32-bit – I previously liked a file grblHAL project based on Raspberry Pi Picoinitiated by Phil Barrett (Brookwood Designs), the person behind The “official” detail board for grblHAL projects, which itself is based on the powerful Teensy 4.2 ARM based board. This official board appears to be available in kit form today, while many others have fallen by the wayside.

If you are interested in 32bit grbl, the a The French project on MakerFr is also worth a lookwhich has an isolated control panel, and what looks like a well-thought-out ‘off-line controller’ (grbl speaking for human-machine interface) that plugs into a Nintendo Wii Nunchuk hand unit – both are based on ESP32 modules.
I was about to buy these boards when I discovered the basic Cronos option.

I’m not advocating the whiteboard I bought because I haven’t tried it yet (so warn the user), but if you want to have a look The ebay ad (from where 2 of the pictures above are taken) is currently here. The same company appears to be doing a similar job 32-bit board four channelswhich ticked a few fewer boxes for me.

#Arduino #based #CNC #controller #separate #stepper #drivers

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