P11

P11 – ESPHome interface for Panasonic air conditioners and heat pumps (CN-CNT)

A small open-hardware board that connects a Panasonic air conditioner or air-to-air heat pump to Home Assistant through the indoor unit's CN-CNT service port. It runs ESPHome on an ESP32-C3 Super Mini with the panasonic_ac component. Everything stays local: no Panasonic cloud and no Comfort Cloud adapter (CZ-TACG1).

This design is based on the Ingenious Makers ESPHome Panasonic Climate Interface. Compared with the original, it:

• uses SMD parts throughout: AO3400A MOSFETs in place of 2N7000, US1A in place of 1N4001, 0805 resistors and an SMD electrolytic capacitor;
• adds an optional on-board DS18B20 temperature sensor;
• is a 4-layer board with solid GND and 3.3 V inner planes.

Features

• Full climate control from Home Assistant: mode, target temperature, fan speed and swing.
• Outdoor temperature, defrost status and live power consumption from the unit.
• Daily energy (kWh) calculated from the power reading.
• Optional room temperature from the on-board DS18B20.
• Powered from the unit's own 5 V on the CN-CNT port, so no extra power supply is needed.
• USB-C on the ESP32-C3 Super Mini for the first flash. After that, updates go over the air.

Hardware

Schematic

You can also get the schematic as a PDF: docs/schematic.pdf.

Level shifter. Each signal uses the classic single-MOSFET bidirectional shifter. The AO3400A gate is tied to +3V3. The source goes to the ESP32 pin with a 10 kΩ pull-up to 3.3 V, and the drain goes to the CN-CNT pin with a 10 kΩ pull-up to 5 V.

Power. The ESP32-C3 Super Mini is powered through its 5V pin from CN-CNT pin 1, and its on-board regulator supplies the 3.3 V rail. D1 sits reverse-biased across the 5 V input and conducts if the cable is plugged in the wrong way round.

Connections

J1 – CN-CNT (pin 1 is the end nearest the board edge, next to U2)

[!WARNING] CN-CNT pin 4 carries 12 V. The board leaves it unconnected, but a cable with the wrong pin order can still put 12 V on the 5 V or signal lines, and that destroys the board and can damage the indoor unit's controller. Check your cable with a multimeter before plugging it in, and always switch the unit off at the breaker before you open the indoor unit.

Cable

The CN-CNT socket on the indoor unit is a JST PA series header, 5 pins at 2.0 mm pitch, which mates with a JST PAP-05V-S housing. J1 on the board is a standard 2.54 mm pin header, so the two need an adapter cable:

• AC end: a JST PAP-05V-S housing with SPHD-001T-P0.5 crimp contacts.
• Board end: a 5-pin 2.54 mm Dupont housing.

Wire it straight through, pin 1 → pin 1 through pin 5 → pin 5. You can leave the pin 4 (12 V) wire out, because J1 pin 4 isn't connected anyway.

Bill of materials

You also need the adapter cable from the CN-CNT socket to J1 (see Cable): 1× JST PAP-05V-S housing, 5× SPHD-001T-P0.5 crimp contacts, 1× 5-pin 2.54 mm Dupont housing with contacts, and some wire.

Any logic-level N-MOSFET in SOT-23 with V_GS(th) well below 3.3 V can replace the AO3400A, for example BSS138 or 2N7002.

Building

1. Order the PCB. Generate Gerbers and drill files from P11/P11.kicad_pcb in KiCad (File → Fabrication Outputs), and order it as a 4-layer board.
2. Solder the SMD parts first (Q3, Q4, D1, R1–R5, C1), then J1 and U2. Watch the polarity of C1 and D1 and the orientation of U2; the silkscreen shows the correct way round for each.
3. Flash the firmware onto the ESP32-C3 Super Mini over USB-C (see Firmware) while it's still loose. Once the module is soldered in, C1 blocks a straight USB-C plug (see Known issues).
4. Solder the ESP32-C3 Super Mini to the board.

Use this top view as a placement reference. J1 pin 1 is on the left, at the board edge.

[!CAUTION] Don't power the board from USB and the CN-CNT port at the same time. Many ESP32-C3 Super Mini clones have no diode between USB VBUS and the 5V pin, so the two supplies would back-feed each other.

Firmware

The ESPHome configuration is in panasonic-cn-cnt.yml. It uses the panasonic_ac external component in cnt mode:

uart:
  tx_pin: GPIO21
  rx_pin: GPIO20
  baud_rate: 9600
  parity: EVEN

climate:
  - platform: panasonic_ac
    type: cnt
    # ...

Before you flash it:

1. Copy secrets.yaml.example to secrets.yaml, in the same folder as the YAML file.
2. Fill in your Wi-Fi credentials, a fallback hotspot password and an OTA update password.
3. Generate an API encryption key with openssl rand -base64 32 and put it in api_encryption_key.

secrets.yaml is listed in .gitignore, so it won't be committed by accident.

Then flash it:

esphome run panasonic-cn-cnt.yml

The first flash has to go over USB. Do it before you solder the module in, or use an angled USB-C cable on an assembled board (see Known issues). If the board isn't detected, hold BOOT while you plug in USB. After that you can update the firmware over Wi-Fi. Home Assistant finds the device on its own through the ESPHome integration.

Known issues

rev 1.0: a straight USB-C cable doesn't fit. On the assembled board, capacitor C1 sits right in front of the ESP32-C3 Super Mini's USB-C socket and blocks a straight USB-C plug. For the first flash you need either:

• to flash the ESP32-C3 Super Mini before you solder it to the board. This is how the prototype was built, and it fits the assembly order above, which fits the module last; or
• an angled (90°) USB-C cable.

After the first flash, updates go over Wi-Fi, so this only affects the first flash and recovering a board that won't boot. If there is a rev 2, it will fix this by moving C1 out of the way of the connector.

Credits

• Ingenious Makers for the original Panasonic climate interface design.
• DomiStyle/esphome-panasonic-ac for the ESPHome component and for reverse-engineering the protocol.

License

This project is licensed under the GNU General Public License v3.0. The license covers the hardware design files, documentation and ESPHome configuration.

Disclaimer

This project is not affiliated with or endorsed by Panasonic. Opening your indoor unit and connecting third-party hardware may void its warranty. You build and use this project at your own risk.

Authors

• Denis Chaplygin - Initial work - akashihi