The 60 GHz fall-detection module (R60AFD1-V) already decides, on its own, whether a person has fallen. It exposes that decision as a single 3.3 V logic pin — GP1 goes High the moment a fall is detected, and Low when the alarm clears. This article shows how to turn that one pin into a local audible / visual alarm with no microcontroller and no firmware: a transistor, a relay, and a buzzer. No serial parser, no broker, no network.
This is the module, not the finished Wi-Fi radar. The finished unit has no exposed GPIO; this article is for integrators building the sensor into their own product or a local alarm.
What GP1 is, exactly
| Pin | Level | Meaning |
|---|---|---|
| GP1 | High = fall detected, Low = clear | Active-high fall alarm |
| GP2 | High = someone present, Low = empty | Occupancy (optional here) |
Two hard facts about the pin:
- It is a 3.3 V TTL logic output. It swings 0 V / 3.3 V, not 5 V.
- It is weak (mA-level). You must never connect a load — relay coil, buzzer, LED string — directly to it. You switch the load through a transistor or MOSFET.
The one rule that prevents burned boards
GP1 switches a transistor. The transistor switches the load. GP1 never touches the load.
Nearly every “it doesn’t work / the module died” case in this setup comes from skipping that rule.
Bill of materials
| Qty | Part | Notes |
|---|---|---|
| 1 | R60AFD1-V module | 60 GHz fall module, UART + GPIO |
| 1 | Logic-level N-channel MOSFET (e.g. AO3400, IRLZ44N) | Gate fully on at 3.3 V. An NPN (S8050 / 2N2222) + 1 kΩ base resistor also works |
| 1 | 5 V relay, or active 5 V buzzer | Relay if you want a dry-contact output; buzzer for sound only |
| 1 | Flyback diode (1N4007) | Required across the relay coil; not needed for a buzzer |
| 1 | 10 kΩ resistor | Gate pull-down, keeps the MOSFET off at boot |
| 1 | 5 V supply, ≥ 500 mA | Module peaks at 300 mA; ripple ≤ 100 mV |
| — | Wires, breadboard / PCB | — |
If you use an NPN instead of a MOSFET, replace the 10 kΩ gate pull-down with a 1 kΩ base resistor between GP1 and the base; emitter to GND, collector to the load.
Wiring
R60AFD1-V Load side (5 V)
┌──────────────┐
GP1 ─┤ GP1 │
│ │ 10 kΩ Gate
│ GND ├───┬───────▱▱───────┤ G
└──────────────┘ │ ├─ N-ch MOSFET (logic level)
│ D ────┤ D
│ S ────┴── GND (5 V supply −)
│
+5 V supply ──► relay coil ──► D (MOSFET drain)
│
1N4007 (cathode to +5 V, anode to D)
│
buzzer / NO contact ──► load ──► GND
Plain-text steps:
- Connect the module 5V and GND to your 5 V supply.
- GP1 → 10 kΩ pull-down → MOSFET gate. Tie the gate to GND through the 10 kΩ so it stays off until GP1 drives it.
- MOSFET source → 5 V supply GND.
- MOSFET drain → one end of the relay coil (or buzzer +).
- Other end of the coil / buzzer → +5 V.
- Flyback diode (1N4007) across the relay coil: cathode to +5 V, anode to the drain side.
- The relay’s NO (normally open) contacts switch your buzzer, siren, light, or any 5 V / 12 V load.
When GP1 goes High, the MOSFET turns on, the coil energizes, and the NO contacts close — the buzzer sounds. When the alarm clears (GP1 Low), the relay releases.
Expected behavior
- Power on: allow ≥ 30 s for the module to boot and stabilize before trusting the output.
- On a fall: GP1 rises to 3.3 V, the relay closes within milliseconds, the alarm sounds.
- Alarm duration: the module’s fall report defaults to 15 s; for production use ≥ 60 s to suppress false trips from someone who stumbles and recovers. (Configurable 5–180 s over UART.)
- Static-dwell (optional): the dwell alarm can drive a second stage after long stillness; default 300 s, production ≥ 30 min.
Add GP2 for “only alarm when someone is present”
GP2 is High when someone is in the coverage area. You can use it to arm the alarm: feed GP2 into the relay coil’s supply path (or a second transistor) so the buzzer only sounds when a person is actually present. This prevents the relay from latching on a stale state with nobody in the room.
Power and false-alarm reality
- Power quality matters most. 4.5–5.5 V, ripple ≤ 100 mV, solid ground. A weak or noisy supply is the #1 cause of unstable detection.
- False alarms are possible. Moving non-living objects (fans, swinging curtains, flowing water) can trip the sensor; a person lying on their side with the chest not facing the radar may be missed. Design redundancy: use GP1 for a fast local alarm and UART / MQTT for logging and confirmation.
- Not a medical device. This is a sensing building block, not a life-safety system. Do not use it as the sole safeguard; not for diagnosis or treatment.
Where to go next
- The GPIO / UART split and the full data set: GPIO vs UART.
- Full module families and specs: Module spec sheet.
- Fall detection tuning and expectations: Fall radar guide.
Evaluation units are on Tindie.