And now for something completely
different…
While perusing the Christmas tat in Poundland /Poundworld recently,
I found some cheap battery powered Christmas lights and thought I could hack
these.
I chose some LED Christmas trees, stars lights and multi-coloured
lights. These take 3v in the form of 2 x
AA batteries, but you can snip the battery holder of and connect them to your
Raspberry Pi or micro:bit.
The first thing I did was to
snip the battery holders off and connect them to my Raspberry Pi, I used some driver transistors to protect
the Raspberry Pi’s GPIO ports. I wrote a
simple Python script using the excellent GPIO Zero library to flash the lights
on and off. This worked well but I had
seen a simple Christmas decoration project in an old book called Digital Electronic
Projects for beginners by Owen Bishop.
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| Lights connected to my Raspberry Pi |
I thought I would build the
circuit to see how well it worked. The
project uses a 555 timer and CD4040BE 12-stage binary ripple counter to make a
set of 5 LED’s light up according to the binary sequence with some additional
add-on extension ideas. I modified the
circuit and replaced the CD4040BE with a CD4042BE 7-stage binary ripple counter
as I didn’t need all of those stages. I added
a UM66T-01L which is a melody generator IC and plays ‘Jingle Bells, ‘Santa
Claus is coming to town’ and ‘We wish you a Merry Christmas’. Finally I added driver transistors to drive
the LED strings as the CD4024BE can’t supply a lot of current via the
outputs.
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| Prototyping the circuit |
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| Prototyping the circuit |
I was happy with the circuit so I transferred it from the breadboard onto some stripboard. Overall I'm very pleased with how it worked out and there's not a single microprocessor in sight.
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| Final circuit built on stripboard |
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| Final circuit schematic |
