🌐 Complete System Integration

End-to-end guide: nRF52840 + iOS + Zwift + Matter

Home / System Guide

System Overview

┌─────────────────┐      BLE        ┌──────────────┐
│   nRF52840      │◄────────────────►│    Zwift     │
│ Fitness Sensor  │    HR & Power    │     App      │
└────────┬────────┘                  └──────────────┘
         │
         │ Matter/Thread
         │
┌────────▼────────┐
│  Thread Border  │ (HomePod mini, Apple TV)
│     Router      │
└────────┬────────┘
         │
         │ Thread Network
         │
┌────────▼────────┐
│   iPhone with   │
│  Control App    │
└─────────────────┘

What You Get

🔵 BLE Broadcasting

Zwift sees your sensor as:

  • Heart Rate Monitor
  • Cycling Power Meter

🌐 Matter Control

Your iPhone can:

  • Turn sensor on/off remotely
  • Adjust workout intensity
  • Monitor connection status

🏠 Smart Home

Works with:

  • Apple Home automations
  • Siri voice commands
  • HomeKit scenes

Complete Setup Process

Phase 1: Hardware Setup (15 minutes)

1. Flash nRF52840 Firmware

# Navigate to firmware directory
cd fitness-sensor-matter

# Build firmware
west build -b nrf52840dk_nrf52840

# Flash to device
west flash

# Verify it's running
screen /dev/ttyACM0 115200

Expected output:

nRF52840 BLE & Matter Fitness Sensor Emulator
============================================
Bluetooth initialized
BLE advertising started
Matter initialized
Ready for commissioning!

2. Verify BLE Broadcasting

  • Open BLE scanner app (nRF Connect)
  • Look for "Bike Sensor Matter"
  • Verify services: Heart Rate (0x180D), Cycling Power (0x1818)

Phase 2: iOS App Setup (10 minutes)

1. Build iOS App

  1. Open Xcode
  2. Create new project with provided code
  3. Add Info.plist and Entitlements
  4. Build and run on your iPhone

2. Setup HomeKit

  1. App opens → Tap "Get Started"
  2. Grants HomeKit permission
  3. Creates home if needed

Phase 3: Pairing Device (5 minutes)

Method A: Via iOS App

  1. In app, tap "+" button
  2. Tap "Open Home Settings"
  3. Settings app opens
  4. Tap "Add Accessory"
  5. Scan QR code OR enter code: 20202021-3840
  6. Wait for commissioning (30-60 seconds)
  7. Name device: "Bike Sensor"
  8. Assign to room: "Home Gym"
Pairing Success Signs:
  • ✅ Green checkmark in Home app
  • ✅ Device appears in control app
  • ✅ Status shows "Connected"

Phase 4: Connect to Zwift (5 minutes)

1. Ensure Sensor is Active

  • Open control app
  • Verify sensor is ON (green heart)
  • Check status: "Broadcasting to Zwift"

2. Pair in Zwift

  1. Open Zwift
  2. Go to Settings → Devices
  3. Search for sensors:
    • Heart Rate: "Bike Sensor Matter"
    • Power Meter: "Bike Sensor Matter"
  4. Tap to pair each sensor
  5. Wait for connection (blue icon)

3. Verify Data Flow

  • Start a ride in Zwift
  • Check your avatar moves
  • Verify HR and power display
  • Values should update every second

Phase 5: Test Control (5 minutes)

1. Basic On/Off

In control app:

  • Toggle sensor OFF
  • Check Zwift: sensors disconnect
  • Toggle sensor ON
  • Check Zwift: sensors reconnect

2. Intensity Control

In control app:

  • Set intensity to 50 (low) → ~105 BPM, ~118W
  • Set intensity to 150 (medium) → ~143 BPM, ~255W
  • Set intensity to 200 (high) → ~171 BPM, ~327W

Watch Zwift display update!

Daily Use Workflows

Option 1: Manual Control

  1. Power on nRF52840
  2. Open control app → Turn ON
  3. Open Zwift → Pair devices
  4. Adjust intensity as needed
  5. After workout → Turn OFF

Option 2: Automated (with Shortcuts)

Create a "Start Cycling" shortcut:

1. Turn on Bike Sensor
2. Set intensity to 127
3. Wait 5 seconds
4. Open Zwift

Activate with:

  • "Hey Siri, start cycling"
  • Home screen widget
  • Automation at specific time

Option 3: Advanced Automation

Morning Routine:

Time: 6:00 AM (Weekdays)
Actions:
  - Turn on Bike Sensor
  - Set intensity to 100
  - Play workout playlist
  - Turn on HomeKit lights

Testing Scenarios

Test 1: Variable Intensity Workout

Simulate interval training:

Time Intensity Expected Power Expected HR
0:00 50 ~118W ~105 BPM
5:00 200 ~327W ~171 BPM (SPRINT!)
8:00 100 ~187W ~138 BPM (recover)
13:00 200 ~327W ~171 BPM (SPRINT!)
16:00 50 ~118W ~105 BPM (cool down)

Adjust via app while riding!

Test 2: Endurance Ride

Set intensity to 127 and let it auto-vary:

  • Power: 220-230W (±10W natural variation)
  • HR: 127-133 BPM (±3 BPM variation)
  • Cadence: 78-82 RPM (±2 RPM variation)

Test 3: Recovery Ride

Low intensity for app testing:

  • Intensity: 30
  • Power: ~91W
  • HR: ~76 BPM
  • Perfect for debugging!

Troubleshooting Common Issues

Issue Check Fix
Zwift Not Seeing Sensor ✓ Sensor is ON in control app
✓ Bluetooth enabled
✓ No other apps using sensor
✓ Device within BLE range (~10m) 		- Close Zwift completely
- Toggle sensor OFF then ON
- Reopen Zwift
- Search for sensors again
Control App Shows "Offline" ✓ nRF52840 has power
✓ Thread border router active
✓ Both on same network 		- Check nRF52840 serial output
- Restart Thread border router
- Re-commission device
Values Don't Update Check serial console for:
HR: 120 BPM | Power: 150 W | Enabled: 1 		If Enabled: 0:
- Turn sensor ON in app

If values frozen:
- Check BLE connection
- Restart nRF52840
Can't Commission Device 1. Reset nRF52840 (power cycle)
2. Remove old accessory from Home app
3. Reset HomeKit: Settings → Home → Reset
4. Try commissioning again
5. Use manual code if QR fails: 20202021-3840

Performance Optimization

Battery Life (if using battery)

Mode Current Draw Runtime (1000mAh)
BLE active ~15mA ~66 hours
Thread active ~8mA ~125 hours
Both active ~23mA ~43 hours

Update Rate Tuning

Modify in firmware (main.cpp):

// Faster updates (0.5 seconds)
k_sleep(K_MSEC(500));

// Slower updates (2 seconds) - save power
k_sleep(K_SECONDS(2));

Advanced Features

Custom Training Plans

Create preset intensity profiles in iOS app:

// Tabata Protocol
func startTabata() {
    // 20 sec high intensity
    setIntensity(220)
    wait(20)
    
    // 10 sec rest
    setIntensity(50)
    wait(10)
    
    // Repeat 8 times
}

Multiple Sensors

Connect multiple nRF52840 devices:

Security Notes

Network Security

  • Matter uses Thread protocol
  • End-to-end encrypted
  • Local network only
  • No cloud connection needed

Privacy

  • No data collected
  • No telemetry sent
  • All processing local
  • HomeKit sandboxed

FAQ

Q: Can I use this with other fitness apps?

A: Yes! Any app that supports BLE Heart Rate and Power sensors (TrainerRoad, Rouvy, Sufferfest, etc.)

Q: Does it work without the iOS app?

A: Yes! BLE works independently. iOS app is just for remote control.

Q: Can I control it from Android?

A: Not with this app, but you could build an Android Matter controller.

Q: What's the range?

A: BLE: ~10m, Thread: ~30m through border router

Q: Can multiple phones control it?

A: Yes! All phones with Home access can control it.

Q: Does it affect Zwift performance?

A: No impact. Zwift only uses BLE, not Thread.

Quick Reference Card

Action Command/Steps
Power On Plug in nRF52840 → Wait 5 seconds
Start Workout Open app → Toggle ON → Open Zwift → Pair
Adjust Intensity Open app → Slide intensity bar → Watch Zwift
End Workout Finish in Zwift → Toggle OFF → Power down
Emergency Reset Unplug → Hold button → Plug in → Re-commission

🎉 You're all set! Happy training! 🚴‍♂️💪

For more details, check out:

nRF52840 Fitness Sensor Documentation

Home | Quick Start | Testing

Copyright © 2025 Darren Soothill. All rights reserved.
Contact: darren [at] soothill [dot] com