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  1. #11
    One thing!

    I can't work out from the silk-screen labelling on that board which of the axis-inputs are ground and which are connected to the inputs to the micro controller.

    If you have a multimeter (and you really need one for this - even a cheap one from Amazon) - you need to check which 6 pins in line on the axis-limits inputs are all connected together - these are the ground returns. For the remaining 6 pins, I expect each pair, for X/Y/Z to be shorted together - these are what you connect the resistors to.

  2. #12
    <deleted>

  3. #13
    Quote Originally Posted by Kitwn View Post
    2v strongly suggests a lack of pull-up resistors which leaves the inputs floating as Doddy has suggested. The inputs are hovering in an indeterminate state and susceptible to every light switch and cosmic particle in the vicinity. No input to any electronics should be left like this and many devices include the pull-up resistors internally, typically 10 Kohms. Some microcontrollers allow inputs to be selected as floating or pulled-up from software.
    ATMEGA328 has an option for an internal 100k-ish pull-up.

  4. #14
    Quote Originally Posted by JeanB View Post
    My switches are wired as NO and when I check the voltage across the + and - pins, I get ~2 volts and if press the micro switch, I get 0 volts. From all the information I gathered, the bottom row of pins are all to ground???? Before changing my switch wiring to shielded wires, I tried, as suggested on the internet, to add a .47µF capacitor across the micro switch………nothing.
    Attachment 27575

    Aha, thanks to Kitwn for making me realise that you're already well aware of the pin layout on the board - I'd missed that bit of your reply in my haste to reply. Hopefully you should be able to understand my earlier ramblings and ignore the bit about identifying the ground-returns on the board.

  5. #15
    I've just had a closer look at the picture and the blue board at the bottom is an Arduino Nano microcontroller board (or clone thereof). If the inputs from the switches are connected directly to the Nano without any other external circuitry then the inputs will be high impedance, floating unless they are specified as ' PULL-UP' in the software configuration.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  6. #16
    Quote Originally Posted by Kitwn View Post
    I've just had a closer look at the picture and the blue board at the bottom is an Arduino Nano microcontroller board (or clone thereof). If the inputs from the switches are connected directly to the Nano without any other external circuitry then the inputs will be high impedance, floating unless they are specified as ' PULL-UP' in the software configuration.
    Completely agreed.

    My gut feeling is the the inputs will be (for god sakes!) configured with internal pull-up. But that is insufficient in this type of environment (it's barely good enough for bench-level development). The problem is not the ATMEGA328 chip, nor the Nano, but the implementation of the Nano onto the Developower board where the use-case should have been well understood by the designer. That board should have had pull-ups/downs on each input to the Nano. It's a poor design, destined to fail and cause frustration wherever it is used.

  7. #17
    Doddy,
    We're obviously both talking at once!

    Re the use of capacitors, the time constant for a .47uF cap and a typical 10K pull-up resistor is 0.47 mS, so a delay of about 1mS will result when the switch opens. Less if the smaller values of resistor are used. The delay when the switch closes depends on the resistance of the switch and the wiring to ground but will only be microseconds. I use 1uF capacitors on the inputs to my traditional cheap Chinese parallel break-out board without any obvious issues with delays and no noise-related false triggering.

    Edit: Just seen your latest post (16) and agree completely. External resistors and noise filtering are a must.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

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  9. #18
    JeanB's Avatar
    Lives in Laval, Canada. Last Activity: 2 Weeks Ago Has been a member for 3-4 years. Has a total post count of 10.
    Good Morning Doddy,

    Thank you for all the info, however, as I am not very good in electronics, would it be easier to install an 8 channel Optocoupler as per Amazon Canada: “Elegoo CA-EL-SM-005”. This would only cost $12.86 and make for a nicer setup?

    (https://www.amazon.ca/ELEGOO-Channel...id=11192166011).

    From my understanding of the pictures, I would plug the micro switches to screw terminals and the Dupont connectors from the Developower board to the pins on the Optocoupler.

    Could I have my micro switches as NC connected to the NC of the Optocoupler since it is a preferred position for security reasons?

    Thanks,

  10. #19
    JeanB's Avatar
    Lives in Laval, Canada. Last Activity: 2 Weeks Ago Has been a member for 3-4 years. Has a total post count of 10.
    Thank you for your help.

    See my answer to Doddy

  11. #20
    JeanB - Yes, to some extent. I don't like it, but it can be made to work:-

    The relay board is low-side switched, so the existing 0V through the micro-switches to the 3 inputs (X/Y/Z) would work. You have to provide a 5V supply to the relay board as well, likely rated around 250mA for 3 relays.

    The relays are change-over contacts, so connect +5V to the NO contact, and 0V to the NC contact and use the pole contact(s) as the drive into the controller card. That way the contact is either connected to +5V or to 0V, without any floating or high-z input resistance at play. The optoisolator input requires a good few milliamps and I think it unlikely to be as susceptible to noise.

    The problem this does introduce is switching time (but not really important) and contact bounce (when the relay switches for a couple of milliseconds). Again, I don't think this is going to be important.

    The bit I said about about NO/NC contacts being +5/0V - can't be arsed working out which way around - try and see. But if you want to change the microswitches from NO to NC then just swap the NO/NC contacts on the relays to match.

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