Here is the pinout for SAE J1772. It consists of a L1 (AC Line 1), L2/N (AC Line 2 / Neutral), PE (GND), PP (Proximity Pilot / Plug Present), CP (Control Pilot / 1 kHz Square Wave).

SAE J1772 Pinout

This is the Signaling Schematic. This shows where signals are generated in the EV handshaking procedure. We'll be signal tapping the EVSE Connector via an adapter.

J1772 Signaling Schematic

This is a TeslaTap, a commercial off the shelf product. It's a passive adapter, which just does pin remapping. I'll be disassembling the J1772 end to gain access to the PP/CP signals.

TeslaTap Passive Adapter

Here you can see the two resistors labeled R6/R7 in the EVSE Connector on the block diagram. This is for the Proximity Pilot. When the mechanical latch is pressed, the 330 Ohm R7 is added causing a voltage shift commanding the vehicle to shut off prior to disconnecting.

R6/R7 Resistors in the EVSE Connector

I used some 3-way Wago 221 Series Lever Nuts to maintain the connection while passing a wire outside of the enclosure. This will allow me to monitor the PP/CP signals.

Wago Lever Nuts for Signal Tapping

Here you can see the 1kHz Square Wave being transmitted on the CP. The vehicle controller looks for this 1 kHz CP before initiating charging.

1kHz Square Wave on the Control Pilot

Here you can see our 1 kHz CP drop from high to low. We have significant activity happening on both the highside and low side when charging initiates.

CP Signal Drop During Charging Initiation

Once we zoom in we can see what looks like a couple of distinct steps at various voltage levels, approximately 20 mV per divission.

Zoomed View of Voltage Steps (~20 mV/div)