z21aio

Async Python library for Z21 DCC command station communication using UDP protocol.

Features

• Pure Python asyncio implementation
• Control locomotives (speed, direction, functions F0-F31)
• Track power control (on/off)
• System state monitoring
• Support for multiple simultaneous Z21 connections
• No external dependencies (stdlib only)

Requirements

• Python 3.10+
• Z21 command station (Roco/Fleischmann)

Installation

pip install z21aio

Or install from source:

git clone https://github.com/botmonster/z21aio.git
cd z21aio
pip install -e .

Quick Start

import asyncio
from z21aio import Z21Station, Loco

async def main():
    # Connect to Z21 station
    async with await Z21Station.connect("192.168.0.111") as station:
        # Get serial number
        serial = await station.get_serial_number()
        print(f"Connected to Z21, serial: {serial}")

        # Turn on track power
        await station.voltage_on()

        # Control locomotive at address 3
        loco = await Loco.control(station, address=3)
        await loco.set_headlights(True)
        await loco.drive(50.0)  # 50% forward

        await asyncio.sleep(5)

        await loco.stop()
        await station.voltage_off()

asyncio.run(main())

Documentation

https://z21aio.readthedocs.io/en/stable/

API Reference

Z21Station

Main class for communicating with a Z21 command station.

# Connect to station
station = await Z21Station.connect(host, port=21105, timeout=2.0)

# Track power control
await station.voltage_on()
await station.voltage_off()

# Get station info
serial = await station.get_serial_number()

# Subscribe to system state updates
station.subscribe_system_state(callback, freq_hz=1.0)

# Clean disconnect
await station.logout()
await station.close()

Loco

Control a locomotive on the track.

# Get control of locomotive
loco = await Loco.control(station, address=3)

# Speed control (-100 to 100, negative = reverse)
await loco.drive(50.0)   # 50% forward
await loco.drive(-30.0)  # 30% reverse
await loco.stop()        # Normal stop (with braking)
await loco.halt()        # Emergency stop

# Function control (F0-F31)
await loco.set_headlights(True)  # F0
await loco.function_on(2)        # F2 on
await loco.function_off(2)       # F2 off
await loco.function_toggle(3)    # Toggle F3

# Get current state
state = await loco.get_state()
print(f"Speed: {state.speed_percentage}%")

DccThrottleSteps

Throttle step modes for locomotive control.

from z21aio import DccThrottleSteps

# Available modes
DccThrottleSteps.STEPS_14   # 14-step mode
DccThrottleSteps.STEPS_28   # 28-step mode
DccThrottleSteps.STEPS_128  # 128-step mode (default)

Examples

See the examples/ directory for complete working examples:

File	Description
basic.py	Quick start - connect, power on, drive locomotive
multi_station.py	Connect to multiple Z21 stations simultaneously
speed.py	Speed control - forward, reverse, stop, emergency halt
functions.py	Locomotive function control (F0-F31)
monitor.py	System state monitoring (current, voltage, temperature)
loco_state.py	Get and subscribe to locomotive state updates

Protocol Documentation

This library implements the Z21 LAN Protocol as documented by Roco/Fleischmann.

Development

Setup

git clone https://github.com/botmonster/z21aio.git
cd z21aio
python -m venv .venv
.venv/Scripts/activate  # Windows
# source .venv/bin/activate  # Linux/macOS
pip install -e ".[dev]"

Enable Pre-commit Hooks

To enable the pre-commit hooks that run flake8 and pytest before each commit:

git config core.hooksPath .githooks

This ensures code quality checks run locally before pushing to the repository.

Running Tests

pytest tests/ -v

License

MIT License - see LICENSE file for details.