TinyG v7 very sensitive to noise/emi?

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  • December 22, 2018 at 11:29 pm #11252
    mkeeley
    Member

    Hi, I have the v7 board. I have updated it to the latest firmware.

    I was trying to get homing to work, and was troubleshooting the homing switches with a multimeter. I discovered that just touching the probe of the multimeter to the limit switch contacts (to check the voltage) tripped the board! (i.e. spindle light flashes, serial console reports a limit switch was hit).

    After some more tests, I tried with the probe completely disconnected from the multimeter i.e. just an un-terminated wire. I can touch just about any point on the TinyG board with my wire, and it trips the limit switches. i.e. motor contacts, earth pins, power pin etc. Not always of course, but a couple of touches will trip it.
    (as a side note, touching the RS485 “A” or “B” with the un-terminated wire puts the board into reset).

    I have some electronics experience, and that seems way more sensitive than it should be. Any ideas?

    December 23, 2018 at 5:10 am #11253
    Zootalaws
    Member

    Earthing problem

    December 23, 2018 at 5:41 am #11254
    cmcgrath5035
    Moderator

    For discussion purposes, you may find these schematic sheets helpful.
    tinyGv7 ports are on this sheet – https://github.com/synthetos/TinyG/blob/master/hardware/v7schematics/DipTrace%20Schematic%20-%20tinyG-v7-pg1.pdf
    tinyGv8 ports are on this sheet –
    https://github.com/synthetos/TinyG/commit/a364308c8800ee2fb2227bb83f5d8edce0aae304#diff-c752e2755161eb51bfb73d76d5581df7

    Simple answer looking at schematic would be yes, v7 pins are likely more sensitive. On v7, all switch ports are pulled high by a 2.7K resistor. If you compare with the typical V8, a 0.22uF chip cap to ground was added to the PCB was added for each port

    Are you sure that unused switch ports are turned off, e.g. $ysx=0 ?
    Are your switches wired with shielded twisted pair, shield grounded at tinyG end only?
    Are you using NC switches ?

    I run a v7, but don’t have Limit switches so can’t compare results.

    Adding something like https://www.ebay.com/itm/20-Wima-MKS2-22uf-100v-5-5mmLS-Metallized-Polyester-Capacitor-0-22uf-63v/283306163530?hash=item41f65cfd4a:g:WpMAAOSwOjBZZQcZ:rk:14:pf:0 right at each port connector might help.

    December 23, 2018 at 6:22 am #11255
    mkeeley
    Member

    yes, unused switches are off. I have 3 set to homing only (xmax, ymax, zmax) and 1 set to limit only (amin) – this is my emergency stop button. They are all NO switches, and that is how I have configured the tiny ($st=0).

    Regarding twisted pair – I can’t see how that would help, as twisted pair is only useful with differential signals (i.e. Data+ / Data-).
    My connector is shielded, but with several connectors running through it (8 core cable). The shield is connected to ground at the board, and each limit switch uses one of the connectors, ground uses one, and three are left unconnected.

    I have some electrolytic caps, I’ll try adding those.

    Do you think the unconnected wires in the cable would cause an issue?
    What about adding the caps at the switch end?

    December 23, 2018 at 8:46 am #11256
    cmcgrath5035
    Moderator

    Maybe a picture of your stuff would help.

    Electrolytic – nope, you need good high frequency cap. 0.22uf ceramic or mylar, etc.

    Make a two wire connection between tinyG and each switch individualy; one wire ground, one wire the other switch terminal. The two wires should be shielded, typically two wire shielded is twisted pair but I understand your comment.
    Twisted pair is what is most available. Connect the shields together and ground them to Vmot “-” terminal. The four ground wires, one from each cable, to the Gnd on port terminal block.
    You can ground the structure of your machine if you want, separately, but do not consider the machine to be grounded for switch wiring purposes

    I could read your description above to say that you run 4 leads plus one ground between tinyG and the machine, but am not sure that is what you are saying. That would inevitably lead to a cable breakout mess at the machine end, as the switches ar in different physical locations.

    This is a good reference to read thru https://github.com/synthetos/TinyG/wiki/Homing-and-Limits-Setup-and-Troubleshooting#limit-switches

    December 23, 2018 at 5:56 pm #11257
    mkeeley
    Member

    Many thanks for your help.

    Here is my machine: 🙂
    Overview
    Zoom
    Hopefully you can see the annotations on the image.

    I built it as an experiment from DVD & Floppy drive mechanisms. It’s also kind of a test to see if I can get the TinyG working with Chilipeppr before I embark on buying a bigger machine (probably a 3020 from AliExpress/Ebay).
    i.e. If I can get the noise problems sorted.

    More details:
    Back Connections
    Zoom
    Back Connections
    The E-Stop is the only one configured as a limit.

    TinyG
    Zoom
    TinyG close up

    Switch
    Zoom
    Homing switch example

    I will try your suggestions and rewire the switches with better cable.

    Do you think connecting the base plates of the drive mechanisms to ground (or the shield wire perhaps) would also help?

    • This reply was modified 5 years, 10 months ago by mkeeley. Reason: Added image links
    December 23, 2018 at 5:57 pm #11258
    mkeeley
    Member

    Hmm, bit small. If you open the images in a new tab you can read them more easily.

    December 23, 2018 at 7:18 pm #11260
    cmcgrath5035
    Moderator

    Wow, cool junk box machine.
    It is amazing what can be fabricated from cast-offs just lying around.

    The 0.22uf conditioning might be enough, but it was early field experience with V7 that has Synthetos recommending NC over NO switches I suspect.

    In CNC world, the term EStop is usually read as an emergency power removal, not just abrupt removal of signalling to motors.
    If the reboot is what you want, it should work but be aware that some folks may misinterpret .

    The behavior you report sounds like limit behavior rather than homing behavior.
    Does you machine behave more normally with the A limit turned off ?

    When you rewire, do connect the sheield drain wires to Vmot- rather than the Port ground connector; keeps any collected noise off the tinyG board.

    And, grounding the base metal directly to Vmot – is probably OK, assuming that there is no other connections to motors or wires. But for sure leave the machine end of the shield drains floating.
    A shielded cable with shield connected at both ends is a great antenna and noise accumulator

    Good luck

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