PLCs and building-management systems in care homes and commercial buildings do not speak MQTT or JSON. They want a dry contact — a switch that closes. The 60 GHz fall module (R60AFD1-V) gives you exactly that opportunity through GP1 (active-high: High = fall detected). With one optocoupler you turn GP1’s 3.3 V logic into an isolated contact the PLC can read, with no microcontroller and no network in between.
This is the module, not the finished Wi-Fi radar. The finished unit has no exposed GPIO.
What GP1 is, and why isolation matters
| Pin | Level | Meaning |
|---|---|---|
| GP1 | High = fall detected, Low = clear | Active-high fall alarm |
| GP2 | High = someone present, Low = empty | Occupancy (optional) |
Two properties drive the design:
- GP1 is a 3.3 V TTL logic output, weak (mA-level). It cannot source a PLC input directly, and it must never see the PLC’s 24 V.
- The PLC side is typically 24 V and a different ground domain. Connecting the two grounds directly invites ground loops and a 24 V fault that destroys the 3.3 V module.
An optocoupler solves both: the radar’s GP1 drives the opto’s LED; the opto’s phototransistor switches the PLC input. The two sides share no electrical connection.
Bill of materials
| Qty | Part | Notes |
|---|---|---|
| 1 | R60AFD1-V module | 60 GHz fall module, UART + GPIO |
| 1 | Optocoupler, e.g. PC817 / LTV-817 | NPN phototransistor output, VCEO ≥ 35 V |
| 1 | Resistor 220–330 Ω | Limits LED current from GP1 (3.3 V) |
| 1 | Pull-up 4.7 kΩ – 10 kΩ | For the PLC side, if required by the input type |
| 1 | 5 V supply, ≥ 500 mA | Module peaks at 300 mA; ripple ≤ 100 mV |
| — | PLC digital input (24 V), wires | Sinking or sourcing per your PLC |
The phototransistor in a PC817 comfortably handles the few mA a PLC digital input draws, and its 35 V rating covers 24 V.
Wiring (sinking PLC input — the common case)
Most PLC digital inputs are sinking: they sink current from an external 24 V through the field device.
Radar side (3.3 V) PLC side (24 V, isolated)
┌──────────────┐
│ R60AFD1-V │
│ GP1 ─┐ │
│ ├──▱▱───┤─── opto LED anode (220–330 Ω)
│ GND ├──────┤─── opto LED cathode
└──────────────┘ │
opto phototransistor
collector ───► 24 V (via 4.7k pull-up if needed)
emitter ───► PLC digital input (Ix)
PLC COM / 0V ───► 0 V
Plain-text steps:
- Power the module from 5 V (4.5–5.5 V, ripple ≤ 100 mV); radar GND is its own domain.
- GP1 → 220–330 Ω → opto LED anode; LED cathode → radar GND.
- Opto phototransistor collector → PLC 24 V (or through a 4.7 kΩ pull-up to 24 V, depending on the input).
- Opto phototransistor emitter → PLC digital input (Ix).
- PLC COM / 0 V → 0 V.
When GP1 goes High, the LED lights, the phototransistor conducts, and the PLC input energizes — your ladder logic sees a fall event and can trigger a call system, lighting, or HVAC. When the alarm clears (GP1 Low), the contact opens. The two grounds never connect.
If your PLC inputs are sourcing instead, swap the polarity: emitter → 0 V, collector → PLC input, and the PLC provides the 24 V internally. The opto still isolates.
Behavior and tuning
- Boot: allow ≥ 30 s after power-on before trusting the output.
- On a fall: GP1 rises; the PLC input turns on within milliseconds.
- Alarm duration: fall report defaults to 15 s; for production use ≥ 60 s to reject someone who stumbled and recovered (configurable 5–180 s over UART).
- Static-dwell (optional): a second stage after long stillness; default 300 s, production ≥ 30 min.
Add GP2 to arm the contact
Feed GP2 (High = someone present) into the loop so the PLC only registers a fall when a person is actually in the coverage area — preventing a stale trigger with the room empty.
Caveats
- Power quality first. A weak or noisy 5 V supply is the #1 cause of unstable detection.
- False alarms happen. Moving non-living objects (fans, curtains, flowing water) can trip it; a side-lying person may be missed. Use GP1 for a fast local/open-contact signal and UART/MQTT for logging; design redundancy.
- Not a medical device. A sensing building block, not a life-safety system; not for diagnosis or treatment.
Module specifications (R60AFD1-V datasheet)
Every figure below is taken from the R60AFD1-V datasheet v2.1 (MicRadar / 云帆瑞达). Nothing here is assumed.
Interface 1 — the connector you actually use (2×3, 2.0 mm pitch):
| Pin | Signal | Level | Notes |
|---|---|---|---|
| 1 | 5V | 5.0 V | Power input + |
| 2 | GND | — | Ground |
| 3 | RX | 3.3 V TTL | UART receive |
| 4 | TX | 3.3 V TTL | UART transmit |
| 5 | GP1 | 3.3 V / 0 V | High = fall alarm, Low = clear |
| 6 | GP2 | 3.3 V / 0 V | High = occupied, Low = empty |
Interface 2 (2×4) is the programming/debug port: 3V3, GND, SWC, SWD, GP3–GP6. GP3–GP6 are spare and user-redefinable.
Electrical (operating):
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| VCC | 4.5 | 5.0 | 5.5 | V |
| Average current (ICC) | — | — | 100 | mA |
| Peak current (Ipeak) | — | — | 300 | mA |
| Operating temperature | −20 | — | +70 | °C |
| Storage temperature | −40 | — | +85 | °C |
Supply ripple must be ≤ 100 mV; the supply must deliver enough current and transient response for the 300 mA peak.
RF and detection:
| Parameter | Value |
|---|---|
| Frequency | 61 – 62.5 GHz |
| Tx power | 8 dBm typ, 10 dBm max |
| Antenna gain | 8 dBi |
| Detection radius (motion / fall / static dwell) | 1.5 m typ @ 2.8 m ceiling |
| Beam angle (horizontal / pitch) | 100° / 100° |
| Motion output latency | ≤ 100 ms |
| Nobody → nobody-absent output | 10 – 60 s |
| Fall detection latency | 5 – 20 s (15 s typ) |
Install and configuration:
- Ceiling mount, vertical down; install height 2.2 – 2.8 m (default height setting 2.3 m — must match the actual height).
- Fall report time: default 15 s, adjustable 5 – 180 s; normal projects use ≥ 60 s.
- Static-dwell report time: default 300 s; normal projects use ≥ 30 min.
- Power-on stabilization: ≥ 30 s before trusting the output.
- Module volume: 35 × 31 × 7.5 mm. Protocol: SIP-S V1.0 (generic UART) and the Tuya standard protocol.
The key point for this article: GP1 is a 3.3 V logic output, not 24 V — which is exactly why the optocoupler is required between it and the PLC.
Where to go next
- The GPIO/UART split: GPIO vs UART.
- Local relay/buzzer from GP1 (no PLC): Local fall alarm.
- Full specs: Module spec sheet.
- Fall tuning: Fall radar guide.
Evaluation units are on Tindie.