Mazzy mini

mazzy mini

A small KiCad PCB for probing and mapping the factory wiring harness of a 2011 Mazda 3-compatible vehicle using a Metra 70-7903 pigtail adapter (403-TS18 harness interface).

What it does

The board plugs into the factory harness via Metra 70-7903 pigtail (the one we ordered, 24-pin + 16-pin connectors) and provides:

• 40 through-hole solder/probe pads (TP1–TP24 for the 24-pin side, TP25–TP40 for the 16-pin side) — one pad per Metra pigtail wire, labeled with known wire color/function or UNKNOWN for unidentified signals. These pads are intended to be soldered to the pigtail wires, not mated as removable connectors.
• SN65HVD230 CAN transceiver on 3.3V, wired to CAN_TX/CAN_RX for a Raspberry Pi Pico 2 W (GP4/GP5) to sniff and identify the 2011 Mazda 3-compatible MS-CAN bus by jumper-probing the unknown pads.
• CANH/CANL screw terminal (J1, Phoenix 1725656) plus CANH/CANL probe pads (TP45/TP46) for jumpering candidate harness wires onto the bus while identifying MS-CAN.
• Onboard 3.3V LDO (AMS1117-3.3) fed from a user-selectable BAT12 (constant) or ACC12 (switched) source via JP1 solder jumper.
• P-channel MOSFET reverse-polarity protection (PMV100EPAR, Q1) with a 15V gate-source zener clamp, plus a unidirectional SMBJ15A TVS clamp at the raw 12V harness input (Q1 pin 3 / VIN_RAW, ahead of the reverse-polarity MOSFET) for ESD and positive-overvoltage protection.
• Optional CAN termination (120Ω R4 across CANH/CANL, DNP by default) — leave unpopulated on the already-terminated 2011 Mazda 3-compatible factory MS-CAN bus. When fitted, place R4 as close as possible to the U1 CANH/CANL pins.
• 3.3V power LED (D1) for quick confirmation that JP1 and the 12V input path are live.
• USB-C 5V input rail (J5 receptacle with 5.1kΩ CC pull-downs, unidirectional 5V ESD TVS (SMF5.0A, D4), and ferrite bead to 5V_USB) exposed to the Pico header for bench Pico power. It does not feed the AMS1117 12V input.
• 3.3V ideal-diode OR (two LM66100 controllers, U3/U4) combines the onboard AMS1117 3V3 and the Pico's PICO_3V3 onto a common 3V3_SYS logic rail (which powers U1) so neither regulator can back-drive or fight the other.
• Rail/debug probe pads — TP41 (3V3), TP42 (5V_USB), TP43 (VIN12), TP44 (GND), TP45 (CANH), TP46 (CANL).

Known wires (24-pin side)

TP25–TP40 are the 16-pin pigtail side; all currently UNKNOWN.

Schematic source

The schematic is defined in Python using SKiDL in circuit.py. Running it generates the netlist used by KiCad.

pip install skidl
python circuit.py

The KiCad project files (circuit.kicad_sch, circuit.kicad_pcb, etc.) are the primary design artifacts and are checked in alongside the source.

JP1 — power source selection

Solder jumper JP1 selects whether the onboard 3.3V regulator is fed from BAT12 (always on) or ACC12 (ignition-switched). Leave it open while mapping unknown harness pins so the board is only powered intentionally.

R4 — CAN termination (DNP)

R4 (120Ω across CANH/CANL) is marked do not populate. The 2011 Mazda 3-compatible factory MS-CAN bus is already terminated at both ends. Only fit R4 if you are running a standalone bench test with no other termination present; when fitted, place it as close as possible to the U1 CANH/CANL pins (at the transceiver, not the connector end).

3.3V ideal-diode OR (U3 / U4)

The onboard AMS1117 3V3 and the Pico's PICO_3V3 are combined onto a common 3V3_SYS logic rail (which powers the SN65HVD230, U1) through two LM66100 ideal-diode controllers. Each device's ~CE pin is tied to the common output, giving automatic reverse-current blocking, so neither regulator can back-drive or fight the other under any operating condition. This replaces the previous JP3 isolation jumper.

USB-C power

5V_USB is routed to the Pico-facing header and its probe pad only; it does not diode-OR into the AMS1117 12V input. However, with a Pico plugged into J4, the Pico's PICO_3V3 feeds the 3V3_SYS rail through the LM66100 OR, so the Pico can power the onboard CAN transceiver (U1) even without the 12V harness supply.