39:I[87087,["$1","$35","$5","$6","$9","$7","$8","$a"],"default"] 3c:I[27201,["$1"],"IconMark"] 3a:Tea7,

There is nothing quite like the feeling of turning a regular house appliance into a fully automated smart device. Today, I am excited to share the first version of my DIY IoT Relay Controller and its companion piece: a portable switch designed to solve a very specific winter dilemma.

The Core Build: The Relay Controller v1

The main engine behind this build is a Wemos D1 Mini paired with a 5V relay and an embedded power supply module. To keep everything safe, compact, and organized, I packaged the entire setup inside a durable, empty plastic electronic project box enclosure.

One of the most critical parts of the design process was building in a fail-safe mechanism. I wired the default mode to the Normally Closed (NC) port of the relay. This ensures that if the microcontroller fails, encounters a software bug, or drops power internally, the light stays on and can still be managed normally via a physical wall switch.

For the electrical interfaces, one side of the case exposes a DIN Rail twin connector with four dedicated terminals:

Negative Input/Output
Positive Input
Output: Normally Open (NO)
Output: Normally Closed (NC)

Relay Controller - My First Custom IoT Relay and Switch Deployment

The Control Ecosystem: From Raspberry Pi to Local LAN

On the software side, the Wemos D1 Mini hooks directly into my home network over Wi-Fi and speaks via MQTT protocol.

The backend architecture consists of:

A local Raspberry Pi running a custom IoT solution designed entirely by me.
An MQTT server acting as the message broker.
A central Web endpoint that exposes a visual dashboard.

The application is reachable inside my local area network (LAN) and securely over the internet. To remove daily friction, I built an auto-login system that identifies known MAC or IP addresses on my LAN, providing instantaneous dashboard access without entering passwords every time. From this web dashboard, I can toggle power or activate an "invert mode" toggle in case I choose to swap the wiring to the Normally Open (NO) channel down the road.

Light - My First Custom IoT Relay and Switch Deployment

Solving the "Cold Winter Night" Problem: The Switch Controller

While having full web controls over the internet is fantastic, using a smartphone to turn off the lights right before bed isn't always the fastest user experience. To fix this, I created a second peripheral: a physical Switch Controller.

This companion device features:

Another Wemos D1 Mini module
A tactical microswitch
A 5V lithium battery charger circuit + battery pack
An optional auxiliary light that can be toggled via the web page

Instead of printing a brand new shell, I repurposed a cheap, portable battery-operated light bought from AliExpress, customizing its chassis to hold my smart hardware.

Remote Switch - My First Custom IoT Relay and Switch Deployment

The primary mission of this device is simple: mapping a physical button to trigger the main Relay Controller across the room. Now, instead of arguing over who has to step out into the freezing winter air to turn off the overhead light, the controller sits right on the nightstand. One tap from beneath the comfort of the blankets, and it's lights out!

3b:Tac1,

Every engineer loves a clean, factory-spec replacement, but true engineering shines when resourcefulness beats supply chain limitations. This was the case when a friend’s universal laptop docking station suddenly lost power. The diagnosis was simple—a frayed wire inside the proprietary, incredibly rare male adapter jack. However, finding a matching replacement part or a whole new adapter in the local market proved to be an operational dead end.

Instead of letting a perfectly functioning docking station become electronic waste, it was time for a hardware intervention. By choosing modification over replication, the station was retrofitted with a standardized power interface.

The Custom Solution

To bring the unit back to life securely, the design strategy shifted toward using a widely available, highly reliable component: a standard 12V universal female barrel jack—the exact type frequently trusted in musical keyboards and consumer electronics.

The modification was executed in a series of precise, modular steps:

Custom Sub-PCB Assembly: The new female barrel jack was soldered onto a generic perfboard snippet to provide strong mechanical stability and neat, strain-relieved wire leads.
Chassis Integration: A carefully measured hole was drilled through the side of the plastic casing, allowing the sub-board to be firmly screwed down into the internal chassis layout.
Electrical Tethering: The leads from the new port were securely routed and soldered directly to the mainboard's primary input nodes, ensuring a low-resistance power path.
Adapter Conversion: The original power brick had its rare proprietary plug snipped and replaced with a heavy-duty matching male barrel jack, ensuring the factory voltage and ampere ratings matched the device's original parameters flawlessly.

Engineering a Lifeline: The Custom Power Port Mod for a Rare Docking Station

Hardware Reborn

Thanks to this clean internal layout, the docking station was successfully saved from the scrap heap. This robust workaround not only solved the immediate booting issue but also permanently upgraded the unit. By moving away from a fragile, proprietary plug to a ubiquitous universal standard, future repairs—should they ever be needed—will take seconds rather than weeks of sourcing.

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