Using a Shelly 1 Gen4 to Remotely Power On/Off a FlexRadio

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Remote station control is one of the most powerful features of the FlexRadio ecosystem. With SmartSDR and VPN access, you can operate your station from anywhere. But one problem remains for many remote setups: how do you safely power the radio on and off when you're not physically there?

A simple and reliable solution is the Shelly 1 Gen4 smart relay, used as a dry contact switch to simulate pressing the FlexRadio power button. This approach is inexpensive, robust and integrates nicely with Node-RED, MQTT or direct API control.

Below is a practical guide based on a real-world remote shack setup. 

Important — Read Before Wiring

This project involves power connections. If you are not completely comfortable working with DC or AC wiring, do not proceed. Incorrect wiring can damage your FlexRadio or create a safety hazard.

This guide assumes you are only using the Shelly relay as a dry contact. Never switch the radio’s main power through the Shelly relay.

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Why the Shelly 1 Gen4 Works Well

The Shelly 1 Gen4 has several features that make it ideal for remote radio stations:

• Dry contact relay (no voltage injected into the radio) 
• Wi-Fi control 
• Local API + MQTT + WebSocket support 
• Tiny form factor 

Most importantly, the FlexRadio remote power pins expect exactly what the Shelly provides: a momentary contact closure, just like pressing the front panel power button.

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How the Flex Remote Power Input Works

The Flex series radio have a remote power control input that acts like a pushbutton.

When the two pins are briefly shorted together:

Pin A -----[momentary contact]----- Pin B

the radio powers on or off.

The Shelly relay simply replicates this momentary closure.

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Hardware Required

For this project you'll need:

• Shelly 1 Gen4 
• RCA cable (cut and stripped for bare leads)
• Wi-Fi access at the station 
• Optional: Node-RED or MQTT broker for automation 

Approximate cost: $15–20

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Wiring the Shelly to the FlexRadio

The Shelly has the following terminals:

O   I   SW   12V   L   N

For dry contact operation we only use I and O.

Flex remote power wiring

Flex Remote Power Pin 1  →  I (Shelly)
Flex Remote Power Pin 2  →  O (Shelly)

That’s it.

The relay simply shorts those two wires when activated.

Do not connect Line (L) or any voltage source to the I or O terminals when wiring the Flex radio. These terminals must only connect to the radio’s remote power pins. Introducing voltage here can damage the radio.

Shelly power

The Shelly itself must be powered using either:

AC Power

L → Line
N → Neutral

or

12V DC

12V+ → +12V
12V- → Ground

Shelly specifies a regulated 12V input. Connecting the device directly to a 13.8V radio power supply is not recommended and may damage the unit unless a regulator is used to step the voltage down.

Do NOT connect the Flex radio power supply through the Shelly relay.
The Flex draws up to 20+ amps on transmit, far beyond what a small relay should switch.

The relay is only controlling the button input, not the radio power.

Before connecting the Shelly to the Flex remote power pins, verify with a meter that there is no voltage present across the pins. The Shelly relay must be used as a dry contact only.

Quick Safety Checklist

• Verify 0V across Flex remote pins before connecting 
• Use Shelly I/O only (dry contact) 
• Never connect L or any voltage to I/O 
• Do not power Shelly directly from 13.8V without regulation 
• Do not switch the radio’s main DC power through the Shelly

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How to Trigger the Power Button


Because the Flex power input is a momentary switch, the Shelly should be triggered using a pulse, not a steady ON command.

Example sequence:

Relay ON
wait 1 second
Relay OFF

This mimics pressing the power button.


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Example Shelly API Command

The Gen4 devices use RPC commands.

To send a one-second pulse:

{
 "method": "Switch.Set",
 "parameters": {
   "id": 0,
   "on": true,
   "toggle_after": 1
 }
}

The relay turns on, then automatically turns off after one second.


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Using Node-RED for Control

In many remote stations Node-RED acts as the automation hub.

Example Node-RED flow:

Dashboard Button
       │
       ▼
HTTP Request / MQTT Publish
       │
       ▼
Shelly RPC Command

A simple Node-RED inject node can trigger the command above to pulse the relay.

This allows you to:

• start the radio remotely 
• shut it down 

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Recommended Remote Station Power Sequence

A reliable remote station typically uses two levels of control.

Step 1 — Turn on the power supply

AC outlet → ON

Step 2 — Wait 5–10 seconds

Allow the power supply to stabilize.

Step 3 — Send Shelly pulse

Shelly relay → 1 second pulse

The radio boots normally.

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Setting Up The Shelly On Your Network

Phone App

Power On: Install the Shelly 1 Gen4 and switch on the power. The device will create its own Wi-Fi access point (AP) and is immediately ready for Bluetooth pairing.

Open the App: Open the Shelly Smart Control app on your smartphone.

Add Device:

Bluetooth (Fastest): If Bluetooth is enabled on your phone, the app should automatically discover the new Shelly device.

Wi-Fi/AP Method: Click the '+' icon (or "Add Device") and select "Scan WiFi for devices".

Connect to Network: Follow on-screen instructions to select your home Wi-Fi network and enter the password.

Finalize: Name the device and it is ready to use. 

Alternative Setup (Web Interface)

If not using the app, you can connect to the device's hotspot (e.g., shelly1-xxxxxx) via your computer's Wi-Fi, then visit 192.168.33.1 in a browser to configure network settings.

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MQTT Integration

Shelly Gen4 devices also support MQTT.

Typical topics look like:

shellies/shelly1g4-XXXX/status/switch:0
shellies/shelly1g4-XXXX/rpc

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Why This Is Better Than Smart Plugs

Many operators try to use smart plugs to control their radio.

That approach has problems:

• sudden power loss can corrupt the radio shutdown 
• no graceful power control 
• potential RF noise from cheap devices 

Using the Shelly relay with the Flex remote power input is much cleaner.

It behaves exactly like pressing the front panel button.

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Sample Node-Red Code

For sample Node-Red code to toggle radio state to On or Standby see: 

https://github.com/n3bkv/shelly-flex-radio-control


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Final Thoughts

The Shelly 1 Gen4 is a fantastic tool for remote ham stations. With just two wires and a simple automation rule, you gain reliable remote control of your FlexRadio power.

Combined with Node-RED, MQTT,and a good VPN connection, it becomes part of a robust remote station infrastructure that can recover from crashes without a physical visit to the shack.

For under twenty dollars, it’s one of the most useful upgrades you can make to a remote Flex setup.

73







 

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