A friend setup his home systems to turn on his PC using Amazon Alexa and tasker to trigger a Raspberry Pi to operate a relay and effectively activate the power button.

What a wonderful idea!

I have a host of Raspberry Pi’s, but instead of Alexa I have chosen the Google Home (Assistant) for my voice control.

My PC is located upstairs from my router and connects using 802.11ac WiFi. Being WiFi that rules out using Wake-on-LAN, which I used to do. So using a RPI to trigger a relay is genius.

As far as the Raspberry Pi goes I’m a coder. I can write code. When it comes to the electronics I really struggle with the electrickery parts.

But all this involves is a single 5v relay. A relay is a switch that uses low voltage to make a high voltage connection. But in my case I’m just using a relay to connect/short the PC’s low voltage motherboard jumper in the same way as the PC’s case power button does.. It’s a momentary low voltage connection that when the motherboard sees connected powers on the the PC.

So all I have to do is replace the power button with my relay and RPI.

The Raspberry Pi

I decided on the Raspberry Pi Zero W. This makes for a very clean small unit that already has WiFi built in so I don’t need a WiFi USB dongle or a Pi HAT.

The idea is the Pi stays connected to my LAN and when I send it the signal it trips the relay.

For processing the signal I need a web service. That’s the bit I talk to and tell it to power on my PC. It’s a RPI so I need a lightweight server with extensions that can talk to GPIO – Node.js and Express!

The Web Service

Using Node.js and Express gave me a simple interface to serve HTTP and handle requests. Add to that the gpio program I can then use Node.js to talk to the RPI GPIO. So now when I send a HTTP request to the Express server Node.js can process it and trigger a GPIO port to do something – like activate a relay.

Taking it a step further I wanted to make it work with my Google Home. The obvious way was to use “if this then that” (IFTTT.com) and a webhook. So now I can talk to my Google Home, it passes the request to IFTTT.com which then sends a web request to my RPI’s express server.

Of course I built in some simple security. You need a token passed in json format to make express process the request.


The Web browser

I then extended the idea of just a web service into a human readable web page interface. So now I can just use a browser to access a form style page and power on my PC using a mobile phone browser – as long as I know the token.

I’ve since added tcp-ping​ and socket.iointo the project so now the web GUI gets updated with when the PC is on or not. I use it to check if port 445 is accessible on the PC and if it is then the web interface updates to show the status.


Items of Note

It’s worth noting that my PC maintains power to one or two USB ports even when it’s off – as long as it’s not off at the wall outlet. So I can power my RPI Zero W from the PC that I’m going to turn on with my RPI. No need of any additional power sockets or transformers.

On Github

You’ll find the full project here: https://github.com/warlord0/scorpion

It works with Node v8