basic-sleep-wake.md

Pressure switch alarm

Introduction Step @showdialog

You can use the ||power:Power|| blocks to control when your micro:bit goes to sleep in low power mode and wakes up to full power mode.

This will help save on batteries when you are running a program for a long time.

You can tell that the micro:bit is saving battery power as the red power LED on the rear of the board will turn off during low-power mode and on during full-power mode.

Simulator support

The power saving extension is not yet supported in the MakeCode simulator, so you will need to flash the program to the micro:bit to try it out.

Make a micro:bit pressure switch alarm @showdialog

In this tutorial you will create an intruder alarm that wakes up the micro:bit when someone steps on a home-made pressure sensor.

It is inspired by the Make it: Code it pressure switch alarm project available on the microbit.org website

Step 1: Start with a basic program

Let's start with a simple program that shows an angry face and plays alarming music when a pin is pressed.

input.onPinPressed(TouchPin.P0, function () {
    basic.showIcon(IconNames.Angry)
    music.playMelody("C5 G C5 G C5 G C5 G ", 120)
})

Step 2: Put the micro:bit to sleep

Displaying a face and playing a melody forever is going to use up battery power pretty quickly. Let's use the ||power:Power|| blocks to save energy before an intruder is detected and after the alarm has been raised

Drag a ||power:request low power|| block underneath the ||music:play melody|| block. After the alarm sounds, the micro:bit will now try to sleep and save power.

input.onPinPressed(TouchPin.P0, function () {
    basic.showIcon(IconNames.Angry)
    music.startMelody(music.builtInMelody(Melodies.Baddy), MelodyOptions.Forever)
    power.lowPowerRequest()
})

Step 3: Tell the micro:bit how to wake up

Good work. You've now told the micro:bit when to go to sleep, but it doesn't yet know how to wake up.

When you use the ||Power|| blocks to put the micro:bit to sleep, you will always need to tell it how to wake up again, otherwise it will just ignore you!

Drag ||basic:on start|| into the workspace and then add ||power:full power on pin P0||underneath ||basic:on start|| to tell the micro:bit to wake up when Pin 0 is touched.

input.onPinPressed(TouchPin.P0, function () {
    basic.showIcon(IconNames.Angry)
    music.startMelody(music.builtInMelody(Melodies.Baddy), MelodyOptions.Forever)
    power.lowPowerRequest()
})
power.fullPowerOn(FullPowerSource.P0)

Step 4: Try it out

Click |Download| to transfer your code.

When the micro:bit has sounded the alarm it will enter low power mode until you touch Pin 0 to wake it up again.

Step 5: Make the alarm @showdialog

Now you have your program, try making a pressure input switch out of cardboard and tin foil like in the picture. Connect the two foil pads on one side to pins 0 and GND on the micro:bit. When you step on the switch, the foil on the top completes an electrical circuit, and it sounds the alert.

More information is available in the Make it: Code it pressure switch alarm project.