i/o shield for limit switches, user buttons and controls

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fjohn624
Posts: 30
Joined: Thu Jan 30, 2014 12:51 am

Re: i/o shield for limit switches, user buttons and controls

Post by fjohn624 » Wed Aug 19, 2015 11:22 am

I'll quickly clarify a few points from what I have read through.

The reason why I originally used opto-isolators was because I had them laying around and I got annoyed trying to tune a RC filter. If you look at the first prototype board, the one that I milled, you can see that it is a very very simple board. It only has isolators for the 3 limit switch inputs and then a terminal strip for connecting the spindle on output and the coolant/vacuum output to be used with SSRs. It is also only one sided so it is fairly easy to mill. The nice thing about the opto-isolators is that they are very easy to tune. I run my switches and inputs with the 24VDC motor power supply. However if I was running a different voltage, the resistors could be changed to keep the same current going to the opto-isolators. You don't have to worry about re-tuning the RC filter. As mentioned by Frank/lordmundi the higher voltage inputs are completely isolated from the arduino and that is good because all the cables that are picking up noise can do that all they want but until that stray voltage can supply enough current to trigger that isolator, we won't get false trips. Basically it turns a voltage driven device (the input on the arduino) into a current driven device. Finally I think its just cleaner, one IC replaces a group of RC devices. You will notice that the last version has quad opto-isolators. Sure I then add an LED but that is just a feature.

The second board was the first OSHpark order. It added more functionality but as mentioned earlier in this thread, I finished it in time for grbl 0.9 to switch the Z LS input and the spindle output around (for good reason) but I took cvoinescu's suggestion and added a 2x2 jumper pin arrangement for the 3rd iteration. I wasn't even planning on making this 3rd board, as I haven't been machining a lot of projects lately and I figured by the time I wanted 0.9 I would have overhauled this shapeoko and maybe bought a new controller (whatever the hot new thing would be by then) but Frank/lordmundi really wanted one so I figured I might as well update it. I am glad I did though.

I wouldn't recommend milling this one unless you really want to do it just for the sake of making it yourself. The reason I say this is that 3 pcb's from OSHpark are $52 shipped. It takes me so long to program/set up a pcb job on my machine, and added complication for doing a 2 sided one that to me its not worth my time. It would be better to find two other people that are interested in doing a group buy to split costs. If you are doing it just for the challenge or you are fairly quick at it, then go for it; I admire that!

I won't pretend that this design is perfect in anyway. I am still new to making my own boards. I have only ever made two boards before starting this project. I will say that putting it on here gave me a few suggestions for improvements, like cvoinescu's jumper suggestion or jjubenv's question about LED viability on the first version leading me to move the leds off to one side so you can see them when the gshield is on top.

I had to compromise on a few things too. At one point I was working on a version to add transistors to the outputs for the spindle and coolant features so that I could provide a 24V output and people could use standard industrial relays instead of SSRs but I realized
1. I had already invested too much time in this project
2. It would make the board bigger as I have to add three transistors plus supporting resistors which adds cost for parts and area of the printed board.
3. If people didn't want that output I would need to add more jumpers so people could use 5V outputs
In the end I realized an SSR is really cheap so the outputs are only a terminal strip. Also I am probably going to switch to a brushless spindle with it's own controller anyway so I will just tie the PWM and reversing wires directly into that.


I am happy to see more interest in this now. Looking forward to see if anyone sets up a group buy, big or small, for these things.

onekk
Posts: 29
Joined: Thu Dec 18, 2014 2:29 pm

Re: i/o shield for limit switches, user buttons and controls

Post by onekk » Wed Aug 19, 2015 12:06 pm

I'm intetested to buy the pcb if there is one available, I'm in Italy so if there are some European to make a group I will be pleased to join.

Thanks for the this project and regards.

Carlo D.

veng1
Posts: 250
Joined: Fri Nov 30, 2012 12:09 pm

Re: i/o shield for limit switches, user buttons and controls

Post by veng1 » Wed Aug 19, 2015 1:36 pm

I could design a new board and get it built if there is significant interest.

I would use optoisolators that have built in Schmitt triggers and probably would not do it as a shield so it would work for any control board. Rather, I envision a terminal strip for the inputs and a terminal strip for the outputs with isolation in between that would be a little more general purpose.

I question whether there is a real requirement for the added I/O or just limit switches are required.

onekk
Posts: 29
Joined: Thu Dec 18, 2014 2:29 pm

Re: i/o shield for limit switches, user buttons and controls

Post by onekk » Wed Aug 19, 2015 1:40 pm

Also the probe input and the buttons i think are intere

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onekk
Posts: 29
Joined: Thu Dec 18, 2014 2:29 pm

Re: i/o shield for limit switches, user buttons and controls

Post by onekk » Wed Aug 19, 2015 1:44 pm

I wrong Hit the enter I think also the probe and the other buttons, are interesting, maybe a modular approach with three or four input pin will be useful to add a second board if chamnit add the jog buttons in future.

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scott216
Posts: 228
Joined: Thu Oct 10, 2013 12:35 pm
Location: New Jersey

Re: i/o shield for limit switches, user buttons and controls

Post by scott216 » Thu Aug 20, 2015 1:56 pm

Brian Stone wrote:I've never milled a PCB, but I'm willing to give it a go. What's the trace width, and what diameter bit would I need to mill this board? I guess I also need a bit to drill the holes, which diameter for that?

I love this 0.010" bit for PCBs: P/N C5 - PB-EM3E8-0100-25V
http://www.soigeneris.com/precise_bits_ ... tails.aspx

I like to make my traces at 0.012" to 0.020". Wider is better if you have room, it just leaves more room for error. <br>
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

veng1
Posts: 250
Joined: Fri Nov 30, 2012 12:09 pm

Re: i/o shield for limit switches, user buttons and controls

Post by veng1 » Thu Aug 20, 2015 2:22 pm

In thinking about this further, I believe the reason I don't have any noise problems is because my limit switches are wired "Normally Closed".

I suspect that if the switches are wired that way and the internal pulls are enabled, there is no reason for optoisolators.

fjohn624
Posts: 30
Joined: Thu Jan 30, 2014 12:51 am

Re: i/o shield for limit switches, user buttons and controls

Post by fjohn624 » Thu Aug 20, 2015 11:13 pm

veng1 wrote:In thinking about this further, I believe the reason I don't have any noise problems is because my limit switches are wired "Normally Closed".

I suspect that if the switches are wired that way and the internal pulls are enabled, there is no reason for optoisolators.
Yes using them in NC mode does help a lot, however I was still having trouble with them especially when the vacuum and dw660 I am using for a spindle would turn on and off. Using shielded cables and adding ferrite chokes to the spindle and vac AC cords helped as well but occasionally I would still get a false trip.

onekk
Posts: 29
Joined: Thu Dec 18, 2014 2:29 pm

Re: i/o shield for limit switches, user buttons and controls

Post by onekk » Fri Aug 21, 2015 9:28 am

I'm interested in the PCB or even in a complete kit

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xfredericox
Posts: 292
Joined: Mon May 04, 2015 10:46 am

Re: i/o shield for limit switches, user buttons and controls

Post by xfredericox » Fri Aug 21, 2015 10:10 am

i would also be interested in a group deal purchase

EU
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