This circuit uses a 555 timer to produce a noise that sounds like a ray gun (similar to that of starwars) that has a changing frequency depending on the value of capacitors and resistors used. It uses basic components such as resistors and capacitors to produce a unique sound. The final product of this project should be a blinking LED and a speaker that produces a laser-like sound. This project is centered around the 555 timer chip. The 555 timer chip has three different modes: monostable, astable, and bistable.

In monostable mode the 555 acts as a pulse timer. It requires a trigger mechanism or input device. The internal comparator sees an input and sets the state of the flip-flop to change the output from a low state to a high state. This allows a connected capacitor to start charging up (this is the case in the Laser Ray Project).

In astable mode the 555 timer outputs a continuous stream of rectangular pulses with a specific period.

In bistable mode the 555 timer alternates between two stable states. An example of this would be a light switch, as it can rest in the on or off position.

IMG_8270.MOV
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Supplies

-Breadboard

-Wires

-555 timer

-220k resistor

-470R resistor

-100n capacitor

-10u capacitor

-white LED

-8R speaker

-power source (6-12v)

Step 1: Construct the Circuit

The constructed circuit shown below will produce our laser ray sound. When constructing your circuit it is important to note which direction your polarized capacitor and LEDs' are facing. Ensure that they are by the length of their legs.

IMG_8270.MOV
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Step 2: What Does Each Component Do in the Circuit?

The 555 timer is currently in a monostable mode, meaning that it will produce a single "pulse" output that is dependent of the values of our resistor and capacitors.

We can calculate the duration of the pulse output by time(t)=1.1*R*C when the Resistor and Capacitor are in series. Once the voltage across the capacitor is equal to 2/3 of the supply voltage, the output of the 555 timer returns to low. The output will remain low until the trigger pin is pulsed again. We determine the amount of time it takes to charge the capacitor by taking the voltage across a capacitor =Vcc*(1-e^-t/(R*C)) and manipulating the equation to solve for t. The result is the equation above (1.1*R*C).

If we use the values of our 555 timer where R = 220Kohms and C = 100nF

t = 1.1*220000*0.0000001

t = 0.0242 sec

t = 24.2 milliseconds

This mean that our 555's pulse will cause the output to go high for 0.0242 seconds. When the trigger pin is high, it will make our pin 7 (discharge pin) drain all charge off of our 10uF capacitor, making the voltage across the capacitor 0. When the pulse is high, the audio output will create the laser sound, the LED will flash, and the 555 timer will return to its stable state. By changing the value of our capacitor to be greater than 100nF we can increase the interval in which the laser ray goes off. A larger capacitor value means a longer charge time.

In the schematic below the speaker is represented by the 8 Ohm resistor in the bottom right. Image one shows the charge being sent to the LED and opening the 10uF capacitor. Image two shows the capacitors charging, which we can see graphically at the bottom of the image.

Step 3: Real Life Applications

This project already has applications in real life projects. We can see this in radar, entertainment, and communication. A primary example of this would be in law enforcement. Police squad cars equipped with with sirens and flashing red and blue lights are a prime example of this 555 timer. Another example of this is modern home security.