So it’s that time of year again. The UK seems to have become more upbeat about Halloween in the last few years, certainly a difference from my youth when trick or treating was distinctly frowned upon! We always get lots of little horrors dropping by so we have a big bowl of treats waiting – along with a little surprise.
You may have seen the ‘Pumpkin Pi’ I made last year, this was a complete hoot and worked very successfully.
This year I thought I’d try something different – and a little more animated! I like the ultrasonic sensor that the Pumpkin Pi uses, it’s really easy to set up and there are loads of resources online – Python is my favourite flavour and it’s really easy to set up simple distance measuring with the sensor which can lead to all sorts of Hocus Pocus.
The initial thought was, I want something hidden that can jump out of a box with a ghastly scream. Achieving that took a fun afternoon of hackery and a lot of bits and pieces I had lying around.
So, to build a motion-sensing-ghoul-in-a-box I used the following recipe:
1 garden fence trellis
1 bicycle inner tube
Lots of scrap wood
Lots of glue, staples, tape and wishful thinking.
1 Raspberry Pi
1 Ultrasonic Sensor
1 mask (35p from Tesco!)
Making the base…
I saw the trellis in the back of the shed and knew that it would be perfect. Getting enough spring for it to ‘jump’ quickly and effectively was going to be tricky. I looked at elastic bands and the few springs I have lying around and none was going to have enough oomph. I’d seen some really powerful catapults made using tyre inner tubes so I found an old one with a puncture and re-purposed this.
I stapled the sliced up tube to the trellis and then attached them to the frame like this..
Then added a small screw as a latch to hold it down under tension (you can’t see the screw in this picture – but you can see it holds it nicely!
Then it was time to go inside and put together the electronics. This was quite straightforward, I set up the sensor and the Python code to measure the distance. I then took a relay board I designed for sHazBot, my PiWars robot and used this to turn a motor backwards and forwards rapidly to act as a ‘trigger’ Releasing something held under load can be tricky but this method works very well.
I 3D printed a little cam to push against the trellis and release the spring…
Time to put it all in the box – added a speaker to play some horrible screams, and a battery so it can all run headless (how appropriate) and it all fitted in nicely.
Finally I added a *really scary* (?!) mask that cost the grand sum of 35p! I also added LEDs to the eyes for extra effect.
Spooky Ghoul-in-a-box – primed and ready!
I think the end result works really well, think I’ll be leaving this out on our front drive on Monday to welcome any callers who may happen to pass by!
The video is a bit dark and best viewed in a dark room. But hey, it’s a horror movie! It’s also a LOT louder when you’re standing next to it (I turned it up to 11)
(No ghouls were harmed in the making of this video.)
Have a terrifyingly happy Halloween everyone!
Until next time..