WEBVTT

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to make my door alarm I've got a new

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make code project let's get rid of the

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on start block but we're going to keep

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the forever block because we're going to

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keep checking the magnetic field

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measured by the microbits magnetometer

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its

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Compass go to logic and find the if

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block and drag that in and also in logic

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you'll find the comparison block so get

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that hexagonal block and drop it on top

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of

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true then if we go to input and click on

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more you'll find a block called magnet

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magnetic force drop it in the first Hole

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In the comparison block and we're going

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to change it so it measures the overall

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strength of the magnetic force your

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microbits magnetometer can measure

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magnetic force in different dimensions

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but we're just interested in just how

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strong it is overall and we're going to

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pop a number in here that we might need

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to change later but I'm just going to

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pick 200 for the moment it measures the

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strength of magnetic field in a unit

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called micro Teslas and I'm going to try

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200 to to start with if the magnetic

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field Falls below 200 micro Teslas I'm

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going to show an angry face because what

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that will mean is the magnet has gone

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away from my microbit somebody's opened

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the door and uh we want to know

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someone's been in the room so it's going

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to show an angry face on the

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display how do I know what number to

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pick for the magnetic force how do I

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know how strong my magnet is well we're

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going to do something to sort that out

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so if we go to input drag in on button a

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press

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and we'll add a show number block and

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let's copy the magnetic force block if I

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right click on it duplicate and drag it

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in here and drop it there what this

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means now is that when I press button a

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I can measure the amount of magnetic

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force measured by my microbit I can see

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it on the

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display so we're ready to try this out

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now doesn't work in the simulator so

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we're going to need to put this on a

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real microbit so uh I'm going to call it

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door alarm and I'm going to download the

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hex file and transfer it to my microbit

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I fix the microbit in the battery pack

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to the door frame using something like

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blue Tack and put the magnet on the door

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itself very close to it have a look on

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the back of your microbit board and see

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where the compass is you need to make

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sure the magnet is close to the compass

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chip on the back of your

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microbit now we can calibrate it with

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the door closed press button a and get a

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reading of the magnetic field strength

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in my case it's around

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453 microteslas

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I'm then going to open the door and

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press button a again and take a reading

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with the door open it's 129 micro Teslas

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now it can still measure some magnetism

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don't forget the Earth is magnetic and

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there are other things probably in my

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house that are magnetic as well so the

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microb bit is still picking up some

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magnetic field so my number of 200

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should work pretty well if it's more

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than 200 it means the door is shut which

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sounds likely cuz with the door shut I

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had 453 micro Teslas if it's below 200

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that probably means someone's open the

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door in this case I know that when my

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door is open I have 129 micro Teslas so

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that should work okay now I should be

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able to tell when someone open my door

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an angry face will appear on my microbit

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display and I'll know that somebody has

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been in my room there are lots of things

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you could do to this project to augment

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it you could perhaps add a delay to give

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yourself some time to get out the room

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remember if you need to reset it you can

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just press button a to show the magnetic

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force again and that will clear the

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angry face off the display on your

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microbit uh maybe you could add an

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audible alarm as well you could add a

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music block so that when somebody opens

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your door it makes an audible sound to

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warn you that somebody has been inside

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your room there are all sorts of ways

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you could modify this

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project