Aircon Auto-Off

A tiny, standalone IR transmitter that automatically sends the “OFF” command to the Hackspace air conditioner at regular intervals.
Designed to prevent the AC unit being left on accidentally.

Powered by a Raspberry Pi Pico WH and an Adafruit IR transceiver module, this device replays the exact infrared OFF signal captured by David Turner and published at:

🔗 https://wiki.hackhitchin.org.uk/index.php?title=User:DavidTurner

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Features

• Sends the AC “OFF” IR command periodically (default: once per hour)
• Uses hardware-timed PIO via the micropython-ir library for reliable IR modulation
• 100% offline — no Wi-Fi or internet required
• Runs indefinitely on USB power
• Compact, neat 3D-printed enclosure
• Simple wiring thanks to the Adafruit IR module with built-in driver transistor

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Hardware Used

• Raspberry Pi Pico WH
• Adafruit Infrared Transceiver Module
  (IR LED + receiver + transistor + resistors onboard)
• The Pi Hut STEMMA JST-PH 4-pin to female header cable
• USB Micro-B cable
• USB wall power adapter
• 3D-printed housing (CAD included in repo)

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Wiring

The Adafruit IR board includes the correct transistor/resistor network, so it connects directly to the Pico:

Pico Pin	IR Module	Function
3V3	VIN	Module power
GND	GND	Ground
GPIO 16	OUT (receiver)	IR input (not used)
GPIO 17	IN (transmitter)	IR output

The IR LED faces outward through the enclosure toward the AC unit.

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Repository Contents

/
├── README.md           ← you are here
├── main.py             ← MicroPython script that sends the OFF IR code periodically
├── ir_tx/              ← micropython-ir library folder (copied from Peter Hinch repo)
│   ├── __init__.py
│   ├── rp2_rmt.py
│   └── ...
└── CAD/                ← CAD source and printing files
    ├── main enclosure.step
    └── ...

main.py

• Contains the raw OFF pulse train captured from the original AC remote
• Configurable interval (OFF_INTERVAL_SECONDS)
• Uses Player class from micropython-ir to replay precise IR timings

ir_tx/

• Local copy of Peter Hinch’s micropython-ir library
• Handles pulse timing using RP2040 PIO

enclosure/

• STL, STEP and CAD files for the 3D-printed housing
• Ensures the IR LED points correctly at the AC unit

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How It Works

1. The AC OFF command is stored as a list of microsecond durations:
   [mark, space, mark, space, ...]
2. micropython-ir generates the pulses matching these timings exactly.
3. The device loops indefinitely:
   • Send OFF pulse train
   • sleep(interval)
   • Repeat

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Installation

1. Flash MicroPython to the Pico WH
2. Copy main.py and the ir_tx/ folder into the Pico’s root directory
3. Connect the IR module using the JST-PH cable
4. Place inside the 3D-printed case with M2 caphead screws
5. Power using USB wall adapter

The unit will immediately begin sending the OFF command at your chosen interval.

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Credits

• Original IR capture:
  David Turner – https://wiki.hackhitchin.org.uk/index.php?title=User:DavidTurner
• IR library:
  Peter Hinch’s micropython-ir
• Hackspace:
  Hitchin Hackspace