IoT Haunted Doorstep - Table of Contents

Project Introduction - Part 1 |  Breadboard Basics - Part 2  | The Build - Part 3 |  Giving it a Try - Part 4

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Welcome to my Halloween project for 2018 - Haunted Doorstep.


The original idea for the project came about when I was playing with a "smart doorbell" idea (which I implemented as a desktop project). Someone suggested, "you have a knocker, why not use that?". I noted the suggestion, and started thinking, how could I make a door knocker smart?


I went through the obvious ideas, mechanically linking it to a switch, using the handle and strike to complete a circuit. Then I stumbled on a tutorial for creating a capacitive touch sensing circuit from scratch. The sensitivity was enough that it could detect touch through glass, or in my case, detect someone about to touch the knocker. Which of course only meant one thing, how can I scare people with this?


Once I had that idea, there was a cascade of additions mostly relating to the specific setup of my house:


Capacitive Horror - Part 1 - Layout



On my road, there is no street lighting, so if I turn off the lights, it is dark! Behind the front door, I have a traditionally switched light, which I can control from a relay. The outside light on the house is a "smart" light switch, which I can send UDP commands from a python script to control. This should allow me to turn off all the lights for any potential trick or treaters, and enhance any other effects.



I have a few little speakers (100W Peak, but physically small, about 100X65X65 (4"X2.5"X2.5")) which should work discreetly in the porch to add some ambience. I can then trigger them when a touch is detected to add to the jump scare. So we will add an amplifier to drive the speakers.



I know I want to do something projected here, but as yet I am not sure what. I have 2 options, rear project something on the back of the blind to the living room window, or project externally, and include the whole of the house. Both are possible, both could be fun, but I am not sure which to do? Whichever I go with will be interactive, so when the capacitive sensor is triggered, the video will react. I am thinking of doing this through web sockets and css animations. This will be nice and responsive and work seamlessly to complete the jump scare effect.



To make this project work, there are some specific bits I will need to get this going:


Product Name
Part Link

Raspberry Pi Model 3

1Product LinkProduct Link

Audio Amplifier-ST Microelectronics  TDA7265TDA7265 which is 2 X 25W Which the power supply can handle and the speakers will be fine with

1Product LinkProduct Link

Mean Well RPD-60A - 12V and 5V 49W power supply. This can provide enough power to the amplifier and RPI.

1Product LinkProduct Link

10M Ω Resistor (10M worked for me in testing, you may need something else, trial and error will tell you!)

1 (ish)Product LinkProduct Link
Some really small capacitors, these might be needed to tune the capacitance for your application.1Product LinkProduct Link


Depending on what you want to actuate with the script, I already have:

  • Speaker (100W peak)
  • Projector
  • VGA over Cat 5 adapters
  • HDMI to VGA Adapter
  • I had a 5V logic optoisolated relay board that I can use to switch the lighting. Of course, you can make your own (or similar) with a relay and transistor. When working with mains, I would always recommend optoisolated - it'll save any nasty incidents with mains voltage and other electronics (like my ethernet network!)

Capacitive Horror - Part 1 - Schematic


Keep an eye out for Part 2 where we will breadboard a prototype capacitive sensing circuit from scratch and the basic code to get it working.