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I am building a small controller box based on an Arduino or similar MCU board.

There are upto 6 buttons on the controller.

In regards to ground, can I daisy chain the ground round all switches? Fundamentally it seems to work ok. For example: Arduino GND--> Btn1 --> Btn2 --> Btn3 etc.

Or is it better to have a single wire to each button from the Arduino GND pin.

This seems an easy way in terms of less wiring.

The wire is 7/0.2 (24AWG).

What are the pro's and cons here?

Additionally, there are 3 GND pins on the Ardunio, why would you use all 3?

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Daisy chaining the buttons will introduce a single point failure in your system: if the wire fails (cut or otherwise) anywhere along the buttons chain, none of those beyond that point will work. You could mitigate this by adding another GND wire in parallel of the first one (the probabilities of failure happening twice at a given location are low, except if you have those wires through a mechanism).

With AWG24 over short distances (you say in a box), you don't even have to take into account the resistance of the wire - and at the frequencies you certainly deal with (since those are mechanical buttons), propagation times of signals do not matter either.

You're fine.

Note that the above ONLY applies to buttons, biased using an extremely low voltage (<50VDC according to BS 7671 18th ed.) using a pull-up sufficiently strong to force next to no requirement on signal quality. This is the case when driving directly from IO pins with internal pull ups enabled on microcontrollers such as Arduinos.

If the number of wires is important to you, you could even chose to use Charlieplexing.

enter image description here

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You can use single ground wire that connects to all buttons in a chain.

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  • \$\begingroup\$ Thanks, ive already established that seems to work, but any pros and cons of doing that wit this type of scenario? \$\endgroup\$
    – Dan Sewell
    May 15, 2020 at 10:57
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    \$\begingroup\$ It's simple and there's less wires that way. There is no benefit from having multiple ground wires, except if the only wire breaks. But why would it, any other wire could break too, and you don't double wire them either. \$\endgroup\$
    – Justme
    May 15, 2020 at 16:47
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Daisy-chaining +ve / -ve lines to inputs / outputs of a controller is standard.

Daisy-chaining safety ground wires between equipment is a no-no as disconnection at one point could render all of them a shock hazard. Single point grounding is a must.

Daisy-chaining ground wires also causes noise and interference in signal paths between systems.

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  • \$\begingroup\$ Are you mixing up safety earth "ground" in mains wiring and current return path "ground" as in battery operated equipment? There will be no shock hazard or noise and interference if the Arduino pushbuttons are wired with a single return wire to Arduino ground pin. \$\endgroup\$
    – Justme
    May 16, 2020 at 10:18
  • \$\begingroup\$ Hi Justme, The first paragraph in my answer shows that we are in agreement as far as common lines of inputs and outputs are concerned. That's how it's always done and there is no problem with that. The second and third paragraphs are not related to that but only mention instances where daisy-chaining is bad. \$\endgroup\$
    – vu2nan
    May 16, 2020 at 11:48

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