2nd TinyG and X limit switch input and SpON not working?!

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  • December 10, 2016 at 8:51 pm #10058
    TayTech
    Member

    Hey guys,
    A few months ago my TinyG decided to give up on the limit switch inputs as in, no 3.3v available on that side of the board. I had played around with a few reed relays (3v with very low ma pull) on the SPon output as I was triggering a secondary 12v relay which connected the 240V to my spindle as there was no other way to activate my spindle through programming. I don’t doubt I accidentally shorted things out or popped something I shouldn’t have so that one went down to my error.
    So the new board arrived and I hooked everything up and this time with a 3V relay with little to no current draw as it says it has up to 30ma or something available on there. I had it work once then disconnected things, powered it down, reconnected everything neater and now my X axis limit input AND SpOn doesn’t work.. no light or voltage output when you type M03.
    I’ve tried resetting all settings on the board etc but nothing. I know its not the limit switch as everything has been tested.. It’s just about the same issue as I had before.
    I obviously have ripped out my 3v relay cause for whatever reason it’s causing the drama but I need to get this X axis limit back working.. the Spindle relay I will work out some other way I guess unless the next board has a 12V switchable relay!
    Help would be very much appreciated as I really want to use this over christmas!
    Cheers
    Mitch

    December 11, 2016 at 5:46 am #10062
    cmcgrath5035
    Moderator

    Mitch – For reference if you have not seen them, schematics are here:

    3V is derived from Vmot by regulator U7. The 3.3V available on pins 1 and 2 of J13 (the limit switch I/O strip) is the same 3.3 V that powers the Atmel device and all the leds.
    From your description, it sounds like tinyG is still communicating with your control computer, but SpOn not working.
    Are other LEDs on?

    Do you still have 3.3V on J13 pins 1 and 2?

    How did you connect your 3volt relay?
    If you connected it from the SpOn port to ground, I doubt the relay would operate, the port pins individually can’t handle much output current(to operate the relay). Solutions include adding an off board 3V logic buffer device or use the SpOn lead to operate a Solid State relay. SSRs use opto isolators on the input stage.

    December 11, 2016 at 10:20 am #10064
    rickcaddell
    Member

    One possible problem with driving relays with a 3.3V output is that relay coils are inductors and have inductive kickback, ie. V = L di/dt. Outputs switch very fast and when the current changes rapidly (di/dt is change in current vs. change in time) across a coil (ie. inductor) the voltage goes very high. This is what may have blown the output, and other things on the board. The best way to power a relay is with a buffer gate like a relay driver. Another way is a diode from the output to 3.3 volts to clamp the voltage so the it does not go much higher than 3.3 volts, or a zener around 3.3 volts from the output to ground.

    December 11, 2016 at 9:43 pm #10068
    Zootalaws
    Member

    Or even more easily/safely with an optical-coupled mosfet, such as in an ssr.

    Small SSRs are wonderful things 🙂

    Oops… edit: I see SSRs were already mentioned. My bad.

    December 11, 2016 at 9:49 pm #10069
    Zootalaws
    Member

    Dr:bs

    • This reply was modified 7 years, 11 months ago by Zootalaws.
    • This reply was modified 7 years, 11 months ago by Zootalaws.
    December 12, 2016 at 9:25 pm #10074
    TayTech
    Member

    Thanks again for your continued support firstly,
    The relay was tiny and was a bitch to connect wires to as it was designed for a PCB, I understand that it may have been a voltage spike on switching so that is good to know for the future thanks! I tried a solid state but the only one I could use was a latching relay and had no way to unlatch it once it turned on… If you guys can recommend one I could find that would be great!
    But back to the issue at hand, the other LEDs light up fine , just not the SpOn light. Also is there a way to get the X axis limit back up? any jumper soldering needed? I had a look at the schematic but my circuit reading skills are on the lower side. I couldn’t see a J13 on the board when I was checking it out on the weekend- where is this located?
    The relay was connected with the coil attached to SpOn and ground- linking the 12V+ and – spliced into the fan output which was set to 12V.

    Hope that helps..!
    Cheers guys
    Mitch

    December 13, 2016 at 9:31 pm #10079
    cmcgrath5035
    Moderator

    Mitch

    The relay was connected with the coil attached to SpOn and ground- linking the 12V+ and – spliced into the fan output which was set to 12V.

    I read this to say you were attempting to use the relay to switch 12V on and off under SpOn control. Can I assume that was for test purposes? The current available from the fan regulator on tinyG will not be adequate to actually run a spindle.

    The challenge with inductive spikes is that they affect circuits rather randomly, similar to ESD damage. It is possible that an inductive spike damaged the silicon chip in the area of of the SpOn output gate which possibly could have affected near by gates, perhaps the X limit inputs. That comment is about adjacent on the die, not necessarily on the pin-out (lead frame).

    Based on the evidence so far in the thread, it seems as if the SpOn output port is no longer functional. I don’t know of any good options to recover it. Perhaps someone else has some ideas

    December 14, 2016 at 7:11 am #10084
    TayTech
    Member

    The 3V relay would pass the 12V from the fan to another relay (12v) which passed 240V/10A (4PDT saddled relay. Worked well- when it worked… haha.
    Ok so I don’t know exactly what all your terms mean but I am guessing it’s gone bang again. is there any possibility to use the 4th axis and its limits instead and somehow change the programming to make A axis the new X?
    Cheers
    Mitch

    December 14, 2016 at 8:43 pm #10088
    cmcgrath5035
    Moderator

    is there any possibility to use the 4th axis and its limits instead and somehow change the programming to make A axis the new X?
    Cheers

    I actually pondered that last night, but I don’t see how to make it work, easily at least. Your could make the A axis behave like a linear axis, but then you would have to translate Gcode that has “X” commands into Gcode with A commands. Messy.
    You could of course run without limit switch, but you would have no homing function either.

    Have you tested any of the other I/O ports, such as coolant or Spindle Direction, just to gauge the extent of damage?
    And to pile on the bad news (sorry), Electrostatic Discharge (ESD) and inductive overvoltage spikes often result in cracks in the oxide layer of the silicon device. Those cracks can then grow over time, due to oxidation of the underlying silicon. So it might work today, but not tomorrow.

    December 14, 2016 at 9:38 pm #10091
    TayTech
    Member

    Ahh, bugger. I’m guessing with custom firmware in the board it could be substituted but not via control software. So I’m guessing for now all I can do is switch the A min limit with the X just to be used as a safety limit instead of homing and just not home it… Could spend another $250+ AUD on a 3rd Tiny G..
    Hmm makes me sad and I wouldn’t get it before Christmas I doubt. I’ll check the damage next time I head up to the workshop.
    Mitch

    December 17, 2016 at 1:25 am #10101
    Zootalaws
    Member

    You could just use a simple contact switch just to get you going – get a length of shielded twisted pair Ethernet cable (cheap as buggery) to run and you should be fine for interference.

    I started with cheap contact switches from a stripped-down 3D printer and never replaced them, because they worked fine and never glitched. I bought a bunch of optical switches – they’re still in their packet, unopened.

    And before you blow up another Tiny, make an opto-electrical isolation board to run all of your external voltages through. 🙂 #hindsightoftheboltedhorse

    • This reply was modified 7 years, 11 months ago by Zootalaws.
    • This reply was modified 7 years, 11 months ago by Zootalaws.
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