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I'm trying to interface a steering wheel control interface with an Arduino.

The interface connector has 6 pins, A to F.
These pins are interconnected with 8 push buttons, SW1 to SW8:

schematic

simulate this circuit – Schematic created using CircuitLab

These buttons don't have a common ground, so I can't connect them directly to the Arduino.

How can I interface these with the Arduino, in order to know which button is pressed?

What came to my mind is creating a network of resistors, injecting +5V somewhere, and reading an analog value that would be dependent on which button is pressed, but I'm not sure how to do that, or even if it is the best solution.

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Hoping that only one button will be pressed at a time, I have a software solution based on polling :

Let A is connected to Pin1, B is connected to Pin2 and so on..

First configure Pin1 as output port and all others as inputs. And out a logic '1' at Pin1. Read the values at Pin2 to Pin6.

  • if Pin2 = '1' then SW1 is pressed.
  • if Pin4 = '1' and then SW5 is pressed.

Now repeat the above steps with Pin2 as output port and others as input ports (Change the conditions accordingly).

EDIT: As Spehro Pefhany commented, this will work for upto two switches pressed simultaneously.

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  • \$\begingroup\$ I think it will work for up to two switches pressed simultaneously. 1+2+5 is indistinguishable from 7 or both 7 + 1+2+5. \$\endgroup\$ – Spehro Pefhany Jul 27 '14 at 18:24
  • \$\begingroup\$ @SpehroPefhany Yes.. I see my mistake. Edited the answer. \$\endgroup\$ – nidhin Jul 27 '14 at 18:31
  • \$\begingroup\$ I think you'd have to configure each input with an internal pull-down (not sure if Arduino has this capability). \$\endgroup\$ – kjgregory Jul 27 '14 at 20:39
  • \$\begingroup\$ @KGregory if the test bit is 0 then internal pull-up can do the job. But I am also not sure if Arduino has this capability. \$\endgroup\$ – nidhin Jul 28 '14 at 3:58
  • \$\begingroup\$ Thanks, Arduino does have the pull-ups, so I've done it this way: pin A to 0, pin B, D and F as INPUT_PULLUP, then read their values. Repeat with pin C against B, F and D, and finally pin E against D and F! \$\endgroup\$ – Benjamin Jul 28 '14 at 9:10

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