Update: Looks like somebody had this idea before me and made a product out of it. Just Google Fake TV. In fact, you can also buy a clone of this from AliExpress – again, just search for ‘fake tv’ in AliExpress. The Chinese versions can be had for about $12 in your hand and that includes a power supply (no doubt of somewhat dubious quality and safety standards). So what follows is a fun project, but it’s easier and possibly cheaper to buy direct from China.
The idea of leaving a light on at home while you’re out is to give the burglar an uneasy feeling that somebody’s at home and it might be worth trying the next house along instead. A TV on at night plays a constantly-changing light-show against your window which really does say I’m at home and I’m awake. Of course, you could leave a real TV on but that’s an eco-disaster since TV’s consume 50W at best and hundreds at worst. Plus you might not want to be burning your TV in for days on end if you’re not at home.
Why not use some of these neopixel RGB LED’s and a microcontroller to simulate the same effect? With just a few eurodollars, an hour of build time and a power budget of 5W absolute maximum, it sounds like a winner.
I used a Digispark for this project since the system is neither demanding in terms of processing nor I/O connectivity. Digspark’s have a USB connector for power input from one of those bazillion USB mobile chargers you now possess. I found a female micro USB to female USB A type socket adaptor on AliExpress (that cost about the same as the DigiSpark).
The light-dependent resistor (LDR) lets the device save power during daylight hours. I fitted a little black tube around the LDR so that you don’t get the LEDs feeding the LDR. Which would be bad. In any case I added some hysteresis to the software to avoid oscillating between day and night modes.
I built using some of my favourite prototyping board. It’s not stripboard (Veroboard) so you have to solder your own wires but it’s cheap, pre-cut to commonly-used sizes. I get mine from eBay – search for ‘prototype PCB’. I had to file down the end of the board so as to not foul the USB connector on the Digispark.
For more detal: Fake TV Security Light