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I have a joystick that is connected to an arcade board. I would like to “listen” for movement on the joystick using a Raspberry Pi or similar. The joystick runs on 12V, and I would be using the Raspberry Pi’s 3.3v GPIO.

Would a relay in series with the joystick signal wire be appropriate for this? If so would a fly back diode be recommended too? This is the relay board that I was looking at (12V): https://s.click.aliexpress.com/e/j9MIN2Y

Are there any precautions that I should take to avoid adversely affecting the existing system?

Thanks!

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A relay is almost certainly NOT the right tool for the job.

The first step in wiretapping an interface in order reverse-engineer it is to determine the nature of the signals you want to look at. For voltage signals, you need a high-impedance buffer amplifier (like the input of an oscilloscope) that will cause minimal disruption to the existing circuit. For current signals, you need a low-impedance shunt or other measurement technology (e.g., Hall-effect), like the input to a milliammeter.

Other kinds of signals (such as capacitive, inductive or resistive sensors) might require some special ad-hoc techniques.

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  • \$\begingroup\$ I'm glad I asked before buying one. Would this coupled with an ADC be any use? i1.wp.com/henrysbench.capnfatz.com/wp-content/uploads/2014/11/… \$\endgroup\$ – Michael Jun 7 '19 at 20:04
  • \$\begingroup\$ @Michael You should first determine if the signal is in fact a current signal and not a voltage or modulated signal. The ACS712 is designed for well one ampere so it's probably inappropriate even for a current-signal joystick. \$\endgroup\$ – nanofarad Jun 8 '19 at 0:55
  • \$\begingroup\$ @AndreyAkhmetov Since I am just interested in whether the circuit is open or closed, does it matter whether I check for voltage or current? As far as I am aware, the joystick mechanism is just a microswitch for each direction, the signal wire goes from the board to the microswitch, and then to ground back on the board. \$\endgroup\$ – Michael Jun 8 '19 at 20:02
  • \$\begingroup\$ Actually, I'm not even particularly interested in which direction the joystick is being moved, so if there was a way to "listen' on the common ground wire coming out of the joystick then that would be even better for me. \$\endgroup\$ – Michael Jun 8 '19 at 20:12
  • \$\begingroup\$ @Michael We've been under the assumption that we're interested in whether the switch is open/closed. If it's such a connection to ground then there's a decent chance that it's a voltage signal; check with test equipment to make certain (since you have the board and joystick available while we have to guess) \$\endgroup\$ – nanofarad Jun 8 '19 at 22:28

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