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