# Hardware & wiring — read before probing

The Cardputer's ESP32-S3 is a **3.3 V** part. Several targets you'll poke are
not:

- Car OBD/USB, PC USB: **5 V** VBUS.
- Some debug headers idle at 1.8 V.

**Always** go through protection. Never land a probe on a live target until
V-Sense has told you the voltage.

## Probe header

`src/core/pins.h` defines `pins::PROBE[]`. By default:

- `G1`, `G2` — the side Grove connector (safe, use these first).
- `G8..G13` — StampS3 pads via a breakout ribbon (optional).

## Minimum protection rig

| Signal        | Between probe and target                              |
|---------------|-------------------------------------------------------|
| Any GPIO in   | 1 kΩ series + 3.3 V clamp (BAT54S to 3V3/GND)         |
| V-Sense (G10) | resistor divider R1:R2 = 2:1 → 0–9.9 V range (ratio 3)|
| Level shift   | bidirectional shifter (e.g. TXS0108) for 5 V buses    |

Adjust `pins::VSENSE_RATIO` if you change the divider.

## USB host

To use **USB Enum** the S3 must supply VBUS to the target as a host. Use an
OTG adapter on the S3 USB port, keep the CDC console on the built-in USB, and
never hot-plug a 5 V target onto a GPIO — it goes on the USB D+/D-/VBUS lines
only.

## Safety checklist

1. Target powered from its **own** supply, common ground with the Cardputer.
2. V-Sense the line first. If it reads ≥ 5 V, shift or stop.
3. Start passive (Pin Scan / UART Sniff). Only replay/TX when you mean to.
4. It's your device. Keep it that way.