My PICnc Build

Raspberry Pi 4 with LinuxCNC 

While researching platforms to upgrade my 3 axis machine my attention was drawn to the prior work of Kinsamanka and Wireb on the github platform.

Wireb built off of the prior Kinsamanka work. 

Searching for examples of projects using PICnc did not get any results. Is the project dead? It seems to be inactive for 7 years as of this writing. 

My investigation into the project convinced me that it was a good starting point. So it was decided to go ahead and use this as the starting point for a Pi – PIC LinuxCNC controller. 

The goal of the project was to: 
Find reliable, readily available, inexpensive compute hardware.
Reduce the footprint of the controller.
Learn a little.
Have some fun.
Add as much flexibility to the system as possible. 

There are two hardware platforms, the Pi and the PIC which necessitates two different software platforms. 

The Pi code was built using Geany and compiled with halcompile. 

The PIC code was ported to use a PIC32MZ, specifically the PIC32-HMZ144, clocking at 200 mHz, from Olimex. This work was done using Microchip MPLAB X IDE v5.40. 

The build has resulted in a system that has: 

32 optically isolated I/O pins, individually selectable as input or output. 
5 optically isolated step & dir outputs 
4 optically isolated pwm outputs  
Stepgen 80kHz default
SPI clock 5 mHz default

Purchased Components: 
RTELLIGENT R60X3 3 Axis Stepper Driver, powered by external linear supply. 
Pi 4, 4gB 
Olimex PIC32-HMZ144 
12 V Supply, generic
5 V Supply, Mean Well LRS 35-5   

My Components: I/O Block – an 8 bit interface, optically isolates the field devices from the logic The block used to interface the stepper driver does not have indicator leds nor their associated resistors installed. This is to reduce potential emi on these high speed lines. The yellow parts are the isolators which are flipped 180 degrees to switch from input to output. This is the electrical function, to change the logic a parameter file is used.  

Bridge – This provides 5V to the Pi and it connects the Pi to the PIC with spi and handshake signals.  

PIC32-HMZ144 Carrier- This board provides the pic to system connections via IDC connectors and it supplies 5 V to the cpu.  

12 V Distribution- a modified I/O Board providing 16 tie points.  

Reference: 

github.com/kinsamanka/PICnc-V2 

github.com/Wireb/PICnc-5axis 

github.com/LinuxCNC/linuxcnc/blob/master...hostmot2/hm2_rpspi.c 


 

I knew that question was going to show up. I did not keep good records so I have a back of the napkin answer for you.

The I/O board was the most expensive to build and I calculate that it cost $8.90.

The Bridge was $3.00

The Pic Carrier $4.75

The PIC32-HMZ144 cost $20.00 (currently about $29 at Mouser).

So what you see of my PCBs the cost is about $35.00. That makes the total cost of the controller in the order of $55.

I know of Mesa but I do not know Mesa products. I think that if you look at total hardware cost you would see advantages to my approach.

If you miss-wire from the field to the Mesa what is the cost?

What is the cost to add opto isolation to the Mesa card?

Mesa cards have fixed number of inputs and outputs (from what I see). The limits of this project is 32 in any combination.

Mesa cards are much faster. Is that important in this project ?

I can add functionality to the pic. Not sure I could do that with a Mesa.

The PIC is currently using less than 2% of data space and less than 2% program space. Lots of room to grow.

I had to repurpose a chassis and was lucky to get everything shoe horned into it.

Time? That is pretty much all I had the last 24 months. Had to do something to keep from going totally bonkers.

Looking good, did you just use wireb's code as is?
Ive had my eye on this picnc fork for a little bit github.com/cnc4less/PICnc-5axis

picnc hasnt had any updates in a while , but its spirit lives on in some of the newer things going on with other microcontrollers.

mesa is great and i will continue to give him my money because you honestly cant beat what they offer(he must be the most patient man alive) , but there is a surprising lack of entry level hardware diversity with linuxcnc , so keep on trucking , olimex is a solid choice also.

The code was modified.

Added a parameter file to define:
i/o pins (p1...p32) as input or output.
specify number of axes, default = 3
specify spi clock rate, default 5mHz
specify stepper rate, default = 80 kHz

Changes were made to the Pi to move the i/o to the pic, synchronize the startup/config process, additional config command, additional config parameters, increased the spi buffer, beacon handling (fault checking) and to check for Pi 4, read and parse the new parameter file.

Changes to the pic was to handle the i/o (glue logic), increased the spi buffer, get the pwm functional, synchronize the startup/config process, additional config command, additional config parameters, no need for compile when changing number of axes.

Thanks