Hello jacczy,
i have all but abandoned using the max31855 directly through my Mesa board, in favor of working on building a Arduino to read temperature, and communicate back to LinuxCNC via Modbus... i just have not gotten around to building it yet.
i have confirmed that the max31855 board will communicate with an Arduino. and it reads temperature correctly.
i have also confirmed that the Arduino can communicate via Modbus with LinuxCNC.
my task will be to build a small enough module that i can mount it on the machine, supply it with 5Vdc, and run a Modbus wire-pair (RS485 RTU) back through the machine, and route that to my LinuxCNC computer. my prototype worked, but was big and ugly.
rather than a official Arduino UNO board, i will be using a self-built with a ATmega328PU, the necessary clock and power filter components, a MAX485 chip, 120R termination resistor, and the MAX31855 board. bare-minimum circuits, and i may possibly POT the circuit in epoxy, where it will ride on the machine, but have not decided on that yet. makes it rather hard to change for a future update...
i was pondering the idea of how to send the temp, a floating-point number over Modbus. i think it allows for an 0-255 integer (byte var), but it occurred to me i can just send the whole-number. i hope my spindle does not reach 255C, as it is only rated for a max of 180C. then, as i am from USA, i use F temp units, and this can be converted once in LinuxCNC from C to F units. it just allows more temp range when transmitted as C units.
