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10. Light Alarm Clock¶

In life, there are various kinds of time alarm clocks. Now let’s make a light-controlled alarm clock. When morning comes, the brightness of light increases and this light-controlled alarm clock will remind you that it’s time to get up.

../_images/10_clock.png

You Will Learn¶

  • Photoresistor working principle

  • Stopping sound playback and stopping scripts from running

Build the Circuit¶

A photoresistor or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity.

Build the circuit according to the following diagram.

Connect one end of the photoresistor to 5V, the other end to A0, and connect a 10K resistor in series with GND at this end.

So when the light intensity increases, the resistance of a photoresistor decreases, the voltage division of the 10K resistor increases, and the value obtained by A0 becomes larger.

../_images/10_circuit.png

Programming¶

1. Select a sprite

Delete the default sprite, click the Choose a Sprite button in the lower right corner of the sprite area, enter bell in the search box, and then click to add it.

../_images/10_sprite.png

2. Read the value of A0

Create two variables before and current. When green flag is clicked, read the value of A0 and store it in variable before as a reference value. In [forever], read the value of A0 again, store it in the variable current.

../_images/10_reada0.png

3. Make a sound

When the value of current A0 is greater than the previous 50, which represents the current light intensity is greater than the threshold, then let the sprite make a sound.

../_images/10_sound.png

4. Turning the sprite

Use [turn block] to make the bell sprite turn left and right to achieve the alarm effect.

../_images/10_turn.png

5. stop all

Stops the alarm when it has been ringing for a while.

../_images/10_stop.png