← Back to Lab Stack
24GHz FMCW Human Presence
Microwave breathing micro-motion radar triggering optocoupled safety interlocks and Adafruit IO telemetry.
Hardware Automation
24GHz mmWave Radar & Thermal Safety System
The Story: A forgotten soldering iron is a fire waiting to happen. Traditional PIR sensors fail when an engineer sits still while soldering. I integrated a 24GHz FMCW millimeter-wave radar that detects chest breathing micro-movements, automatically controlling high-current AC relays with a cloud safety watchdog.
| Parameter | Engineering Specification | Design Notes |
|---|---|---|
| Radar Principle | 24GHz FMCW Doppler Radar (LD2410) | FMCW frequency sweep 24.00GHz – 24.25GHz |
| Sensing Sensitivity | Detects human chest breathing displacement ≥ 0.2mm | Zero false-off while engineer sits motionless |
| Detection Gates | 8 distance gates (0.75m per gate, max 6.0m) | Independently tunable threshold energy per gate |
| Galvanic Isolation | PC817 Optocouplers (3,750 Vrms Isolation) | Zero electrical path between 3.3V logic and AC mains |
| Relay Switch Rating | Songle SRD-05VDC-SL-C (10A @ 250VAC) | Flyback 1N4007 diode suppression on coil |
| Safety Watchdog | Hardware FreeRTOS watchdog + 300s software timer | Audible piezo buzzer warning 30s before auto-shutdown |
| Signal Name | Wire Color | Source Pin | Target Pin | Protocol / Notes |
|---|---|---|---|---|
| 5V VCC Supply | Red | 5V Rail | LD2410 VCC & Relay VCC | 5V regulated ≥ 1A rail powering coils and radar |
| Ground Rail | Black | GND | Common DC Ground | Isolated from AC Mains earth |
| Radar Presence Out | Yellow | GPIO 14 | LD2410 Pin 4 (OUT) | GPIO High (3.3V) = Person Present, Low = Idle |
| Relay 1 Trigger | Orange | GPIO 26 | PC817 Pin 1 (via 330Ω) | Opto Soldering Iron AC Mains cut-off control |
| Relay 2 Trigger | Violet | GPIO 27 | PC817 Pin 1 (via 330Ω) | Opto Hot Glue Gun / Auxiliary bench rail control |
| AC Mains Live IN | Brown | AC Live | Relay 1 & 2 COM Terminals | 230VAC 50Hz Mains input (1.5mm² double insulated) |
| AC Mains Out (Iron) | Blue | Relay 1 NO | Soldering Station AC Socket | Normally Open; energizes only when occupant confirmed |
- FMCW Doppler Radar: Detects human micro-presence up to 6 meters with zero false shutdowns while an engineer is concentrating.
- Optoisolated AC Mains: PC817 optocouplers isolate 3.3V logic from 230V mains, driving Songle 10A SPDT relays.
- Closed-Loop Cloud Sync: Streams live relay states and ambient DHT22 telemetry to Adafruit IO with real-time UI reflection.
LD2410 24GHz Radar
Optocoupled Relays
Adafruit IO
DHT22
MQTT