By Steve Bush 20th January 2023
After a time with a multimeter and scope, the othewise-undocumented Cronos board for home-build cnc machines has revealed some of its secrets.
Overall, it seems like a proper grown-up design with a few quirks.
Power rails are well thought out (see below) and seem well up to the job, and isolation (including power and ground isolation) is fully implemented on-board to separate the microcontroller and USB power domain (together, ‘MCU domain‘ from here)from the cnc-machine-connected power domain (‘cnc-domain‘ from here) – so little chance (that I can see) of current being shoved up the USB into the controlling PC by a fault on the machine side.
The following information is from rough notes – so check it yourself before relying on it:
Firstly: the non-screw connectors seem to be 2.5mm pitch (not 0.1in) and of the JST XH style.
To handle power, there are a couple of dc-dc converters (diagram right – the XL4015 is nominally a 5A part and the XL1509 is 2A) and an un-regulated dc-dc isolator to provide the various voltage rails. The 326P-style microcontroller is fed via a couple of Schottkys from either the USB control/programming mcu domain input, or from 5V derived from the 12 – 36V domain input (called ’36V from here) via galvanic isolation (by a Mornsun B0505LS-1WR2)
The pulse, direction and enable outputs to external drivers (diagram left) are all opto-isolated on-board. This is laudable, although every separate driver I have ever found has opto-isolators on its inputs for these signals, so this is over-kill in many circumstances. Step and enable outputs (not the direction outputs) are via fast (<1μs) opto-isolators, and all finally emerge finally via cmos buffers powered from the cnc domain 5V, which is directly linked to the main 36V ground.
From the diagram, the axes outputs are labelled:
As mentioned above, the ‘ENA’ enable output to the external drivers does not have its own counter-terminal. Instead has z-axis PUL+ terminal nearby for cnc domain 5V, or the cnc domain 0V which is three terminals the other way.
This 0V is part of the ‘FCES’ group (diagram right) which has:
Next comes a 36V cnc domain PWM fan output (see circuit diagram above) where the +ve is directly connected to the 36V power input and the -ve is modulated to 0V of cnc domain via a hefty mosfet.
Lastly on that connector is the spindle output and, just like the 36V fan output, the connections are: +ve directly connected to the 36V power input and -ve modulated to 0V from the cnc domain by another hefty mosfet. Again: this pwm information is also available as the 0-10V analogue signal mentioned above.
The rest of the connections are pretty well described by the power circuit diagram (repeated left) and the annotated board photo (just above).
The x, y and z-limit and probe inputs are all via on-board opto-isolators (simply a 2k4 resistor in series with the input led in each case), and the off-line controller connector appears to be for the simple controllers that are available for small ‘3018’ cnc machines.
For non-USB programming the mcu, there is a row of bare pads on the rear for a bed-of-nails or similar.
Now time needs to be found to wire then thing to the drivers and the steppers on the mill – with all the necessary fans, and other odds and sods.
Your email address will not be published. Required fields are marked *
Download the Elektra Awards 2022 media pack and book your sponsorship package to be part of the most prestigious awards event celebrating its 20th anniversary this year!
Get our news, blogs and comments straight to your inbox! Sign up for the Electronics Weekly newsletters: Mannerisms, Gadget Master and the Daily and Weekly roundups.
Read our special supplement celebrating 60 years of Electronics Weekly and looking ahead to the future of the industry.
Read the Electronics Weekly @ 60 supplement »
Read the first ever Electronics Weekly online: 7th September 1960. We've scanned the very first edition so you can enjoy it.
Read the very first edition »
Electronics Weekly teams up with RS Grass Roots to highlight the brightest young electronic engineers in the UK today.
Read our special supplement celebrating 60 years of Electronics Weekly and looking ahead to the future of the industry.
Read the Electronics Weekly @ 60 supplement »
Read the first ever Electronics Weekly online: 7th September 1960. We've scanned the very first edition so you can enjoy it.
Read the very first edition »
Tune into this Xilinx interview: Responding to platform-based embedded design
Tune into this podcast to hear from Chetan Khona (Director Industrial, Vision, Healthcare & Sciences at Xilinx) about how Xilinx and the semiconductor industry is responding to customer demands.
By using this website you are consenting to the use of cookies. Electronics Weekly is owned by Metropolis International Group Limited, a member of the Metropolis Group; you can view our privacy and cookies policy here.