The Sunrise Wake-Up Alarm

In this tutorial, you’ll learn how to build a sunrise wake-up alarm. It’s a light-sensitive circuit that will activate a buzzer when you have light shining directly on it. Place it in your window at night and the alarm will activate in the morning when the sun rises.

This circuit uses an active buzzer that works with 9V. Find the breadboard diagram and full parts list below the video.

The Components You’ll Need

  • 9V Battery
  • Breadboard
  • Wires (For example Dupont male-to-male)
  • LDR: Photoresistor
  • Q1: Transistor BC547
  • R1: Resistor 1 kΩ (replace with a potentiometer to adjust sensitivity)
  • Buzzer: Active (9V)

To test this circuit, I recommend you connect it on a breadboard since it’s quick and you can easily try different resistor values. If you decide that you want this more permanent, you can solder it onto a stripboard or even make your own PCB design out of it.

Below you can see how I connected this circuit on a breadboard:

Sunrise wakeup alarm on a breadboard

How The Circuit Works

This circuit is very similar to the Automatic Night-Light Circuit. But while the night-light turns on the transistor when it gets dark, this circuit turns on the transistor when it gets light.

The photoresistor and the resistor make up a voltage divider. And to understand it, you should also know how the transistor works.

When it’s dark, the photoresistor will have high resistance – much higher than R1. That means the voltage divider gives a low voltage out to the base of the transistor and it stays off. When the transistor is off, the buzzer is deactivated.

When there is a lot of light shining directly on the photoresistor it will have low resistance. This will give a higher voltage out to the base of the transistor so that it turns on. This means the buzzer gets activated and starts making sound.

The sunrise wake-up alarm on a breadboard


Did you build this circuit? Do you have any questions about how it works or how to build it? Let me know in the comment section below.

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5 thoughts on “The Sunrise Wake-Up Alarm”

  1. Sir u r amazing. U teach very impressively. I m addicted watching your vedios.
    I am looking for such simple circuits. I want to understand the working of each component when it is connected to the circuit. I can understand zener diode, diode, led, resistor, working seprately i mean in very simple circuit.
    But when a big circuit made up. I got confused.
    For example – In a AC to DC converer circuit I can understand only up to output voltage from bridge rectifer after that i how to add capacitor, zener etc..
    I m very eager to learn.

    Plz make a vedio on plastic ferrit transformer in ac dc converter .. How these are used…

    Plz keep making such vediod like sunrise wake up circuit…. It is simple circuit and use of each component is clearly visible..
    Thanks a lot sir

  2. Sir keep making such simple circuits. I have watched many vediod from different sources.. But they all didn’t help me a little bit. But your one vedio have done it… U r amazing.
    May Allah prosper you. Have a good health sir..

  3. Going to use the light sensitivity circuit to determine when male is delivered .When mail is delivered and mail box is opened light hits phototransistor alarm will go off.

  4. Hei! Jeg er student ved en ingeniørlinje for telematikk, og går tredje semester. Dette semesteret har et elektrofag der vi skal levere et prosjekt. Jeg har tatt inspirasjon fra guiden din om “sunrise wake-up alarm” og ser at du bruker en buzzer. Jeg har lyst å ha en annen lyd, og ser derfor på muligheten for å kjøpe en ferdig programmert lydchip, og en liten piezo speaker, er dette noe du tenker kan være mulig? Har du noen tips?

    • Ja, dette er absolutt mulig. Dette er ikke en kjempebra krets, men det er lett å bygge med få komponenter. Et problem med denne kretsen er at strømmen til basen til transistoren styres av LDR’en, som igjen påvirker hvor mye strøm som er tilgjengelig for hva enn du styrer via transistoren. Så du er avhengig av at LDR verdien i lys er lav nok.

      Mitt tips er å teste ut kretsen så raskt som mulig. Ikke planlegg deg ihjel. Bygg, test, forbedre ;)


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