Goblin detector and Jam review – a guest post from 8-year-old Annabel

Liz: Annabel Oakley is eight years old. That makes her our youngest ever guest blogger! Here’s her account of a day out at a the PyCon UK Raspberry Jam in September at Coventry University, and the goblin-scaring project she made with her Raspberry Pi. Thanks very much, Annabel – and thanks also to Dad, who helped out with the Goblin Detector and drove the car!

Annabel wanted a project to show at the  computer conference. She decided to make a Goblin Detector which would sound a buzzer and flash a light, when her brother or sister went in her bedroom.


Annabel used a Raspberry Pi computer and a motion sensor.

Annabel and goblin detector
Her dad showed her what to do, and Annabel wired it up and wrote the program to control it.

goblin detector
The program was written in a computer language called Python. The Goblin Detector has a motion sensor in a margarine tub. It connects to the Raspberry Pi using three wires.


The Raspberry Pi has an add-on called Pibrella which gives it three lights, a buzzer and a button. It waits 5 seconds to let you get out of
the room, then it waits for movement. When it sees movement, it sounds a buzzer. You can press the button to stop the buzzer, and it will wait for movement again.

The motion sensor is very cheap, only £3, and can be found in light switches which turn off automatically. It has three wires:

• Positive
• Signal
• Negative

The program waits for a high current on the Signal wire, which means it has seen some movement. You can find out how to make and
program one yourself on Annabel’s dad’s website.

Then Annabel and her dad set off for the computer conference. The ticket was only £5 for children!

Annabel, book
When Annabel got there, she got given a goody bag which included a brand new Raspberry Pi, a book and other goodies!

Annabel wrote a program to put the words “Hello World” on the screen in Minecraft.


Some teachers were also at the conference. The teachers were learning how children used computers.

There were also some computer programmers helping the children and
teachers. The grown-ups were not allowed to touch the keyboards. The children had to do everything themselves! There were lots of grown-up computer programmers around to help out, and some of the children were already experts.

Lots of people were interested in Annabel’s Goblin Detector.

We let the children take it apart and program it for themselves. It was easy to put it back together.

Most of the children at the computer conference were girls. There was a whole pack of Brownies!


Annabel also saw some robots which  could be programmed to dance.

Annabel made a friend called Sam and they wrote a program to take lots of photos, and then turn those photos into an animated video.

sam and annabel
There were some famous programmers helping out, such as Carrie Anne Philbin and Ben Nuttall, who work for the Raspberry Pi charity.

Miss Philbin, famous programmer
Sam and Annabel had to show off their animation to everyone else.


You can watch their 8-second animation here.



Link for “make and
program one yourself” should of course be:


…let’s hope my server holds up under the load. I’ll shift it to a larger server if it gets slashdotted (gods bless the cloud!).

Any questions, I’ll try to answer them here and might even be able to get Annabel to answer them in person between 6pm and bedtime (BST).


Yoink – sorry! I’ll fix that right now.


Thanks Andrew and thanks Liz and team. Great read for my kids.


This was great! How I wish we could get things like this to happen in the states.


You can. Just find a venue and announce it on Twitter. Connect with the Raspberry Jam people to help promote. Ask for it to be listed in Pi Weekly newsletter.
Did 5th Jam on the 5th October.
About 20 people turned up with projects to show and another 20 came to be inspired.

It’s amazing how little effort is needed to get a Jam setup.
There appear to be a lot of people looking for local Jams like yourself just waiting for someone to kick it off.


And watch this space tomorrow: Jams are about to become even easier to set up and promote.


Glad you enjoyed PyCon UK (I’m one of the organisers of the event). We couldn’t have done it without the help of the RaspberryPi Foundation and their amazing education team. We’re already planning next year’s event. :-)


It was great meeting Annabel and Sam, I was really impressed with their animations at PyConUK Raspberry Jam. But I’m sad that their first animation did not get a mention, so I’ve uploaded it! We call it ‘The many faces of Alex Bradbury’. In fact he was directed not to move for continuity reasons by the directors. He is taking it to Sundance next year.




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