Some basic MESA questions

I'm new to LinuxCNC and the MESA boards, and I'm trying to understand some things. The following is my current understanding of how this works. Please correct me if I'm wrong.

First, the boards differ in how they are connected to a PC. There are PCI boards and there are Ethernet boards. The main difference is basically where the board is located.

Then there are daughter boards which extend the capabilities of the mother boards. They are connected by a DB25 cable or RS485 connection. The daughter boards cannot work without the mother boards.

The next characteristic is, how many I/Os a board has. Being an FPGA, an I/O can be programmed to be anything: input, output, serial, PWM, etc... Given the requirements, one must choose a board with enough I/Os or extend it with a daughter board.

The I/Os may be equal from the FPGAs view, but they are not equal wrt to their electrical characteristics. A 'normal' I/O has a 5V TTL level, can sink or source only small amounts of current and is not short circuit resistant. So you need a board that fits to your sensor or actors. Or you use a TTL board and do all the protection and level shifting yourself.

Correct so far?
Next step would then to list and count the number and type of I/Os I have on my machine and find the MESA board that fits best.

Thanks

Thanks. The 7i95 seems to be sold out everywhere, but the 7i96S is available, and it seems to be enough for me (for now).

Some other questions I had and found the answers before I could ask

Can I use a RPi: yes, but it is slow. So I will repurpose an old iMac.

I have a Huanyang inverter for my spindle. How do I connect it to the MESA board? Answer: I don't. LCNC will talk through USB - RS485 with it (although I would like to have a hardware enable signal for it. I guess that is possible, but a problem for later).

Last but not least is power supply. I guess I'll need 2-3A @ 5V.

I guess that's all I need to know for now.

I was just reading through the manual on the 7i96 i ordered. Didnt realize there was only one encoder input for the spindle. I have three closed loop steppers, sounds like ill need a daughter board perhaps?

or.... iguess the stepper doesnt send the encoded signal to the 7i96s normally but i was reading am index home can be accomplished this way... which would be nice.

Thanks for this post and the help also, after researching CNC mill conversion and settling on LinuxCNC, the favorite card to use 7i76e seems to be sold out everywhere.

I will also grab a 7i96s based on the friendly advice given here. I guess if we run out of I/Os we can always add something like the 7i73 later.

Carlos wrote:

I guess if we run out of I/Os we can always add something like the 7i73 later.

7i84 is better unless you are building a HMI

Thanks for the response @tommy. I’ve ended up going the route you suggest. I’ll make a nice rigid (as rigid as am able) 3 axis and see how it goes. I am giving myself a nice working volume if I decide to add a 4th/5th later. I’m looking at 250x250x250mm. That seems to be a nice size and gets me under the standard 2 foot extrusion order sizes so I can still match cut them so I keep my squareness.