Local Fall Alarm From a 60 GHz Radar Module: Driving a Relay and Buzzer From GP1, No Firmware

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.