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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.

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  • \$\begingroup\$ What is 'PCA' and 'PPP' which are asterisks but never explained? Why is PPP the third signal and how does this relate to the first and second signals (which you fail to identify as such? Is PPP the middle connection of the jack plug which is connected LOW when the switch is not pressed and goes HIGH (or open circuit? - please clarify which) when it is? BTW its optocoupler not octocoupler. I'm certain if you simply did a sketch of a 3.5mm jack plug and labelled it you'd answer question 2 for yourself. (common is usually another way of saying ground or 0V) \$\endgroup\$ – JIm Dearden Jul 19 '16 at 9:47
  • \$\begingroup\$ @JImDearden, the asterisks lead nowhere, reason why I am asking As from my understanding I suppose "PCA" mean Principal component Analysis but no idea what is PPP \$\endgroup\$ – chris Jul 19 '16 at 9:52
  • \$\begingroup\$ en.wikipedia.org/wiki/Switch#Contact_terminology \$\endgroup\$ – JimmyB Jul 19 '16 at 9:54
  • \$\begingroup\$ "Should we rather use a relay or an octocoupler to simulate this SPDT switch ?" - If you don't know anything else about the circuit (voltage, polarity, current) you really should use a relay. \$\endgroup\$ – JimmyB Jul 19 '16 at 9:56
  • \$\begingroup\$ To me, it looks like PCA and PPP are defined just there. PCA is the push button, normally open, connected to "common" a.k.a. "low" when activated. PPP "is low if the cable is connected and the pendant is not pressed", so it's just the inverse of PCA, i.e. the other contact of the SPDT. \$\endgroup\$ – JimmyB Jul 19 '16 at 9:59
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  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).

enter image description here

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.

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