Cryoswitch Controller

Terminal-accessible control system for two independent cryo/RF switches driven by a Teensy microcontroller. Designed for remote operation over SSH.

Architecture

┌──────────────┐   USB Serial    ┌──────────────┐   4-bit one-hot   ┌───────────┐
│  Host PC     │ ──────────────► │   Teensy     │ ────────────────► │ Switch 1  │
│  (Python CLI)│   115200 baud   │              │                   └───────────┘
│              │ ◄────────────── │              │ ────────────────► ┌───────────┐
│  SSH access  │                 │              │                   │ Switch 2  │
└──────────────┘                 └──────────────┘                   └───────────┘

Each switch is controlled by 4 GPIO pins in a one-hot encoding:

• Channel 0: 0000 (all off)
• Channel 1: 1000
• Channel 2: 0100
• Channel 3: 0010
• Channel 4: 0001

Quick Start

1. Flash the Teensy

Open cryoswitch_control.ino in the Arduino IDE (or PlatformIO), select your Teensy board, and upload.

Pin mapping:

Switch	Pin 0 (CH1)	Pin 1 (CH2)	Pin 2 (CH3)	Pin 3 (CH4)
Switch 1	5	4	3	2
Switch 2	23	22	21	20

2. Set Up the Host

On the Linux machine connected to the Teensy:

cd host/
sudo bash install.sh

This will:

• Install pyserial via pip
• Add your user to the dialout group (for serial port access)
• Create a udev rule so the Teensy appears as /dev/cryoswitch
• Install a cryoswitch command you can run from anywhere

After first-time setup, log out and back in for the dialout group change to take effect.

3. Use It

# Interactive mode (auto-detects the Teensy)
cryoswitch

# Or specify port explicitly
python3 host/cryoswitch_cli.py --port /dev/ttyACM0

# One-shot commands (great for scripting)
cryoswitch --cmd "SET1 3"
cryoswitch --cmd "SET2 1"
cryoswitch --cmd GET

Interactive Commands

Command	Description
s1 <0-4>	Set switch 1 to channel (0 = off)
s2 <0-4>	Set switch 2 to channel (0 = off)
off	Turn both switches off
status	Query current state from device
help	Show command reference
quit	Exit (turns switches off by default)

Safety feature: On exit, the CLI sends an OFF command to turn all switches off. Use --no-safe-off to disable this if you want switches to remain in their current state after you disconnect.

SSH Remote Access

The whole point of this tool is SSH access. On any machine that can SSH into the host:

ssh user@host-machine
cryoswitch

That's it. The CLI is pure terminal text — no GUI, no X forwarding, no port forwarding needed.

For scripted/automated control from a remote machine:

ssh user@host-machine "cryoswitch --cmd 'SET1 3'"
ssh user@host-machine "cryoswitch --cmd GET"

Serial Protocol Reference

All commands are newline-terminated ASCII at 115200 baud.

Host → Teensy

Command	Description
SET1 <0-4>	Set switch 1 channel
SET2 <0-4>	Set switch 2 channel
OFF1	Turn off switch 1
OFF2	Turn off switch 2
OFF	Turn off both switches
GET	Query current state
ID	Device identification
PING	Heartbeat check

Teensy → Host

Response	Meaning
OK <sw1> <sw2>	Command succeeded
STATE <sw1> <sw2>	Response to GET
ERR <reason>	Error (e.g., ERR INVALID_CHANNEL, ERR UNKNOWN_CMD)
CRYOSWITCH V1	Response to ID
PONG	Response to PING
READY	Sent on boot

Troubleshooting

Problem	Solution
Permission denied: /dev/ttyACM0	Add yourself to dialout: sudo usermod -aG dialout $USER, then log out/in
No Teensy found	Check USB cable, try ls /dev/ttyACM*, or specify --port manually
No response from device	Teensy may need a reset; unplug and replug USB
/dev/cryoswitch doesn't appear	Re-run sudo udevadm control --reload-rules && sudo udevadm trigger
Box-drawing characters look wrong	Ensure your SSH terminal supports UTF-8 (export LANG=en_US.UTF-8)

File Structure

cryoswitch_control/
├── cryoswitch_control.ino   # Teensy firmware
├── README.md                # This file
└── host/
    ├── cryoswitch_cli.py    # Python terminal UI
    ├── requirements.txt     # Python dependencies
    └── install.sh           # One-shot host setup script