to make my door alarm I've got a new
make code project let's get rid of the
on start block but we're going to keep
the forever block because we're going to
keep checking the magnetic field
measured by the microbits magnetometer
its
Compass go to logic and find the if
block and drag that in and also in logic
you'll find the comparison block so get
that hexagonal block and drop it on top
of
true then if we go to input and click on
more you'll find a block called magnet
magnetic force drop it in the first Hole
In the comparison block and we're going
to change it so it measures the overall
strength of the magnetic force your
microbits magnetometer can measure
magnetic force in different dimensions
but we're just interested in just how
strong it is overall and we're going to
pop a number in here that we might need
to change later but I'm just going to
pick 200 for the moment it measures the
strength of magnetic field in a unit
called micro Teslas and I'm going to try
200 to to start with if the magnetic
field Falls below 200 micro Teslas I'm
going to show an angry face because what
that will mean is the magnet has gone
away from my microbit somebody's opened
the door and uh we want to know
someone's been in the room so it's going
to show an angry face on the
display how do I know what number to
pick for the magnetic force how do I
know how strong my magnet is well we're
going to do something to sort that out
so if we go to input drag in on button a
press
and we'll add a show number block and
let's copy the magnetic force block if I
right click on it duplicate and drag it
in here and drop it there what this
means now is that when I press button a
I can measure the amount of magnetic
force measured by my microbit I can see
it on the
display so we're ready to try this out
now doesn't work in the simulator so
we're going to need to put this on a
real microbit so uh I'm going to call it
door alarm and I'm going to download the
hex file and transfer it to my microbit
I fix the microbit in the battery pack
to the door frame using something like
blue Tack and put the magnet on the door
itself very close to it have a look on
the back of your microbit board and see
where the compass is you need to make
sure the magnet is close to the compass
chip on the back of your
microbit now we can calibrate it with
the door closed press button a and get a
reading of the magnetic field strength
in my case it's around
453 microteslas
I'm then going to open the door and
press button a again and take a reading
with the door open it's 129 micro Teslas
now it can still measure some magnetism
don't forget the Earth is magnetic and
there are other things probably in my
house that are magnetic as well so the
microb bit is still picking up some
magnetic field so my number of 200
should work pretty well if it's more
than 200 it means the door is shut which
sounds likely cuz with the door shut I
had 453 micro Teslas if it's below 200
that probably means someone's open the
door in this case I know that when my
door is open I have 129 micro Teslas so
that should work okay now I should be
able to tell when someone open my door
an angry face will appear on my microbit
display and I'll know that somebody has
been in my room there are lots of things
you could do to this project to augment
it you could perhaps add a delay to give
yourself some time to get out the room
remember if you need to reset it you can
just press button a to show the magnetic
force again and that will clear the
angry face off the display on your
microbit uh maybe you could add an
audible alarm as well you could add a
music block so that when somebody opens
your door it makes an audible sound to
warn you that somebody has been inside
your room there are all sorts of ways
you could modify this
project