SPDT simulation, relay, optocoupler or something else?

Question

I am currently working on a project where we have to pilot the command of a machine via a remote control based on some input.

Normally, the remote control is a simple push button but we are working on making this push button to be activated based on some logic, hence we need a mcu to send a signal to the machine to simulate a push button which is normally mechanic.

We are currently designing the remote control schematic and PCB but first we have a small doubt on one point:

The machine user manual mention this:

The remote is a normally open SPDT switch connected to the machine with a 1/4 inch stereo phone jack. The sleeve contact of the phone jack is at common, the tip contact is the normally open signal PCA*. The jack is metal threaded and bulkhead mounted on the rear of the device. A harness connects the jack to the MCU PWA with a 4 pin, locking, polarized connector.

Activation of the switch results in signal PCA going low as long as the switch is held. The third signal PPP*, is low if the cable is connected and the pendant is not pressed. This provides positive identification of a correct and functioning remote control

A few questions:

1. Should we rather use a relay or an octocoupler to simulate this SPDT switch ?
2. I don't very well understand what they mean by "The sleeve contact of the phone jack is at common, the tip contact is the normally open signal PCA". How do you understand this ?

EDIT: the asterisk lead nowhere.

Answer 1

1. You can use a sealed signal relay (< 2A) such as an Omron G6. There are other options, but the relay is straightforward and should just work.

2. A 1/4" stereo plug has three electrically isolated parts- the tip, the ring and the sleeve (image from this site, ignore the balanced, hot/cold designations).

It's not entirely clear from the verbal description how the switch is to be connected other than that the N.O. contact goes to the tip. I could make an educated guess (N.C. to ring and common to sleeve), but it would be much better to get even a hand scrawled schematic from the supplier.