light activated buzzer project

Discussion in 'The Projects Forum' started by tacalert, Mar 14, 2012.

  1. tacalert

    Thread Starter New Member

    Sep 14, 2011
    Hello Everyone,
    I signed up for the forum seeking some help. My goal is to create a light activated buzzer - so when I hit it with a laser a buzzer sounds, exactly like this one shown on the video:

    I have found a circuit diagram for what I am looking for here:

    but I dont know what everything means or how to assemble it.

    Hoping someone with patience can school me.

    Thanks in advance
  2. enigma121

    New Member

    Mar 8, 2012
    You've already done most of the work it seems!

    First off if you're new to electronics (like me) its a good idea to get to know the symbols used for each component.

    There is loads of information on the internet regarding this. Just Google 'Electronic symbol' for more than enough results to keep you going.

    First of all power!

    The symbol at the top of the diagram (arrow pointing up) indicates a power source (in this case the positive terminal of a 9v battery/power supply). At the bottom of the diagram is an inverted triangle made up of horizontal lines. This represents ground and in the case of your diagram would be the negative terminal of the same 9v batter/power supply.


    In the case of your diagram the jagged lined component with R1/R2 etc written next to them are resistors. Each one has a value in Ohms (Ω). The ones required for the circuit pictured are 100KΩ (Kilo-Ohms), 4.7KΩ and 10KΩ.

    Still on the subject of resistors there is a light dependent resistor (photo resistor) in your diagram too.

    Obviously you have a buzzer in your diagram - again you can order this easily - Google is your friend. The wire going into the top of the buzzer (in the diagram would be your +ve (+9v)

    The item in the centre of the diagram is a LM741 Operational amplifier. Google 'LM741 Datasheet' to view specifications of the component. The numbers surrounding it represent the pins on the chip. The datasheet will allow you to match up these pin numbers with the actual chip.

    Finally, the last symbol in your circuit (circle with rectangle and arrow coming out of it) is a transistor. Google '2n222 transistor datasheet' to show you how the 3 pins on the transistor match up with your diagram.

    Best way forward would be to order the components from your local/online electronics shop (I use maplins but I'm UK based).

    Also buy single core wire, a 9V battery and a breadboard (basically a breadboard allows you to put the circuit together without soldering). This makes it easy for you to take apart and try again when something goes wrong!

    Hope this helps
    tacalert likes this.
  3. tacalert

    Thread Starter New Member

    Sep 14, 2011