Smol Pairing & Calibration

Overview

This guide covers how to pair, calibrate, and update your Smol Slime trackers and receiver. You’ll use a serial terminal (such as nRF Connect or PuTTY) to run setup and troubleshooting commands.

Table Of Contents

• Setup & Software
• Pairing Trackers (First Time)
• Adding More Trackers
• Calibrate Trackers
  • Basic Calibration
  • 6-Sided Calibration
  • Magnetometer
• Update Firmware (Optional)
• Troubleshooting
  • Linux: SlimeVR Server Cannot Detect Receiver
  • Trackers Paired but Not Appearing in SlimeVR Server
• Reference
  • Receiver Commands
  • Tracker Commands
  • Button Shortcuts
  • Status Codes

Setup & Software

You’ll need a serial terminal program to send commands to your trackers and receiver.

• Recommended: Download and install nRF Connect for Desktop.
  • Install the Serial Terminal module inside it.
• Linux/Mac:

  • sudo screen /dev/ttyACMX 115200
    

    (Find your port with sudo dmesg.)
• Windows Alternative: PuTTY

Pairing Trackers (First Time)

When first flashed, trackers and receivers boot into pairing mode automatically.

1. If the devices are not in pairing mode:
   • Receiver: Run pair
   • Tracker: Hold the SW0 (Function) button for 5 seconds (or short RST/GND 3 times)
     • The LED blinks once per second while in pairing mode.
2. Watch for esb_event output in the receiver console:
   • <inf> esb_event: Added device on id 0 with address 95CB23A0FDF7
3. Plug the tracker into your computer via USB.
4. The tracker’s LED flashes four times once pairing is successful.
5. Repeat for all trackers.
6. Exit pairing mode by entering exit on your receiver.

Adding More Trackers

You can pair individual trackers to your receiver one at a time using the add command (on the receiver) and then the set command (on the tracker).

1. On the tracker, run: info
2. Copy its "Device Address" (e.g. 95CB23A0FDF7).
3. On your receiver: add 95CB23A0FDF7 (replace the device address with yours).
4. Copy the pairing ID from the receiver output:
   • [00:46:06.485,778] <inf> esb_event: Pair the device with D94BDEF1E442005B
5. On your tracker: set D94BDEF1E442005B
6. Confirm pairing on the tracker — you should see:
   • [00:30:51.060,028] <inf> esb_event: Paired
7. Repeat all steps for each additional tracker.

Calibrate Trackers

Basic Calibration

The basic calibration runs an accelerometer and gyroscope zero rate offset. This is usually all you need. There are two methods. When calibrating, place the tracker flat on a surface and keep it still until the LED indicates completion.

• Method 1: Press the SW0 (Function) button twice, then wait until the LED blinks four times to confirm calibration.
• Method 2: Connect your tracker to your computer and run calibrate.

6-Sided Calibration

The 6-sided calibration aligns the accelerometer across all six axes. This method requires you to hold the tracker perfectly still on all 6 sides.

1. Connect your tracker to your machine while it is powered on.
2. Run the 6-side command.
3. Place the tracker on each side as prompted. The console will tell you when to rotate, or you can watch for the LED success blinks.

Magnetometer

Magnetometer calibration is disabled by default. When enabled, it runs automatically — no button or command required. Slowly rotate your tracker 360° on each of its six sides while it’s flat on a surface.

The LED will blink when you place it flat on each side and will blink continuously when it is ready to save.

Update Firmware (Optional)

For flashing new trackers and receivers, check the Flashing Firmware Guide.

1. Download the latest firmware version from Pre-Compiled Firmware.
2. Connect your tracker to your computer via USB, and ensure it is powered on.
3. Run the dfu command in your terminal.
4. Your tracker will appear as a USB drive labelled SLIMENRFTRK or NICENANO etc. (depending on your tracker hardware)
5. Copy the UF2 firmware file to your tracker.
6. If your tracker isn't paired after update, see Adding More Trackers.

Troubleshooting

Linux: SlimeVR Server Cannot Detect Receiver

For Linux systems, a udev rule may need to be created for the SlimeVR Server to detect your receiver as an HID device.

Create the rules file:

touch /etc/udev/rules.d/99-hid-dongle.rules

Add the following rules to the file:

sudo tee /etc/udev/rules.d/99-hid-dongle.rules > /dev/null <<'EOF'
SUBSYSTEM=="usb", ATTR{idVendor}=="1209", ATTR{idProduct}=="7690", MODE="0666"
KERNEL=="hidraw*", SUBSYSTEM=="hidraw", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="7690", MODE="0666"
EOF

Ensure it worked:

cat /etc/udev/rules.d/99-hid-dongle.rules

Note: You may need to update the idVendor and idProduct values for your receiver. Use lsusb to find the correct IDs.

Trackers Paired but Not Appearing in SlimeVR Server

• On your receiver: exit.
• Reboot the tracker: reboot or press the SW0 button.
• Reboot the receiver: reboot.
• Ensure the IMU is detected on the tracker: info.
  • Functioning: IMU: ICM-45686
  • Non-Functioning/Not Detected: IMU: None

Reference

Receiver Commands

• info - Get receiver information
• list - Get paired trackers
• reboot - Soft reset the receiver
• pair - Enter pairing mode
• add <address> - Manually add a tracker
• remove - Remove last paired tracker
• exit - Exit pairing mode
• clear - Clear stored trackers
• dfu - Enter DFU bootloader
• uptime - Get receiver uptime
• meow - Meow!

Tracker Commands

• info - Get tracker information
• reboot - Soft reset the tracker
• battery - Get battery information
• scan - Restart sensor scan
• calibrate - Calibrate sensor ZRO
• 6-side - Calibrate 6-side accelerometer
• mag - Clear magnetometer calibration
• pair - Enter pairing mode
• set <address> - Manually set receiver (Receiver's add command must be completed first)
• clear - Clear pairing data
• dfu - Enter DFU bootloader
• uptime - Get tracker uptime
• debug - Print debug log to troubleshoot tracker or firmware
• reset <type> - Reset calibration/stats for "zro", "acc" (6-Sided enabled only), "mag", "bat", or "all"
• meow - Meow!

Button Shortcuts

• Reset - 1 Press
• Calibration - 2 Presses
• Pairing Mode - Press and Hold for 5s
• DFU Bootloader - 4 Presses
• Deep Sleep - Press and Hold for 1s

Status Codes

Status codes consist of one or more status values (added together) listed below:

Created by Shine Bright ✨, Depact and Seneral. Edited by Brisfknibis.