CNCFia

CNCFia

The idea with this board is to provide a generic shield/daughter card for 3.3V MCUs running CNC firmwares like GRBL (and its ports) and g2core. For that, instead of making a shield with specific sockets, we decided to provide a pin header that can be used to connect to different MCUs.

Included capabilities

Switches

There are six opto-isolated connectors for limit switches (X, Y, and Z Min/Max limits), a Probe connector and an extra opto-isolated connector to be used for any generic function, and five non-opto isolated ones to be used for external controls (Door security, Emergency Stop, etc).

The opto-isolated switches have an option to be powered by an entirely separated power source to provide full electrical isolation.

All the switches are pulled UP via 4.7kΩ resistors, intended to be used with NC (normally closed) switches connected to the GND, making it an active low signal. Take that in consideration when wiring/configuring the software.

External driver control/level shifting

Support for nine voltage shifted outputs, mosfet (2n700X) driven. Enough to provide Step/Pulse/Enable signals for three external drivers (those usually have a 5V control voltage).

The mosfets connect the outputs to GND, so when wiring make sure to provide the 5V common wire to all positive (+) signals and the outputs to the negative (-) signals.

TODO example

Jumper Settings

Connector Descriptions

TODO add descriptions and image

Electrical notes

View this project on CADLAB.io.

All calculations were made considering a 3.3V output from the driving MCU pins, while keeping the output currents under 10 mA, what should be safe for most of the MCUs around.

The 3904s driving the relays have a base current (Ib) of ~ 7.8 mA, that should be enough to saturate the transistor and provide the 78 mA needed by the relay coil.

The LTV-847s are used with typical values for Vf and If, according to datasheet specs.

The OPAMP output for the spindle can be regulated with a potentiometer and from the 3.3V PWM it can get values close to 11V with a 12V power source. Simulated circuit shows a 0.4s approximately time to get to the stable voltage.

License, Copyright and disclaimers

Copyright Jose Junior jose.junior@gmail.com 2020.

This documentation describes Open Hardware and is licensed under the CERN OHL v. 1.2.

You may redistribute and modify this documentation under the terms of the CERN OHL v.1.2. This documentation is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE. Please see the CERN OHL v.1.2 for applicable conditions.