I ordered a J1772 connector from China for around $100 and got a big surprise during prototyping my EVSE circuit. I thought about using a micro-controller but realized its not really needed as I didn't have a development environment. But when I looked into the J1772 Proximity function, I realized the S3 switch and 150/330 Ohm resistors must be built into the plug. The one I received had the proximity pin wired to the cable (like the pilot conductor/pin) and the latch had no S3 switch or the 150/330 resistors. I made the dumb mistake of assuming even a Chinese J1772 plug manufacturer would have properly dealt with the proximity function - my bad assumption. Before you buy one anywhere, make sure they have implemented the proximity function in a manner that will work correctly as returning it can be difficult. I suspect they may have sent me a prototype without the proximity implementation.
The latch which releases the plug from the receptacle must be tied the J1772 defined S3 switch which causes the EV to see the 150+330=480 Ohms when the latch is pressed so it can cut its current draw to prevent arching upon removal. While engaged, S3 is closed presenting 150 Ohms to the EV so the EV knows its safe to draw current. I'm going to need to either buy another J1772 plug/cable or implement the proximity with a disconnect switch on the EVSE. Its still much cheaper than buying one. That of course requires the operator to know to engage an EVSE switch before pulling the plug out - not fool-proof.
The latch which releases the plug from the receptacle must be tied the J1772 defined S3 switch which causes the EV to see the 150+330=480 Ohms when the latch is pressed so it can cut its current draw to prevent arching upon removal. While engaged, S3 is closed presenting 150 Ohms to the EV so the EV knows its safe to draw current. I'm going to need to either buy another J1772 plug/cable or implement the proximity with a disconnect switch on the EVSE. Its still much cheaper than buying one. That of course requires the operator to know to engage an EVSE switch before pulling the plug out - not fool-proof.