The non-inverting input(+) of one comparator is connected to the 1/3 output of the voltage divider and the inverting input(-) of the other comparator is connected to the 2/3 output of the voltage divider. These resistors create a voltage divider circuit with the value of 1/3 and 2/3 of the supply voltage as pin 1 is ground and pin 8 is Vcc. This is from where this IC got its iconic name. PIN 1 and PIN 8: These are connected between the ground and Vcc with three 5kΩ resistors. The internal circuit of the 555-timer is discussed below: It’s the oldest piece of tech and thus you can rely on it blindly and best of all, it’s affordable. When it comes to designing timer circuits, the very first thing which comes to mind is the 555 timer IC. The list of components required for designing a police siren circuit is given below: Components Required for Designing 555-Timer based Police Siren Previously, we have also built a siren generator circuit using UM3561 IC but for this tutorial, we will be using the more commonly available 555 Timer Circuit. For demonstration, I designed the circuit on the breadboard. In this project, we will use the astable mode of this IC with some external components to generate a police siren tone. We have discussed the working of all these three modes previously, you can check them out if interested. If you know a little about electronics then you must have heard of 555-timer IC and its 3 very popular circuits the astable multivibrator, the bistable multivibrator, and the monostable multivibrator. You’ll be surprised to know that the brains behind these tones are not a microcontroller but a humble NE555 timer IC. If you want to support me subscribe to my YouTube Channel: Ģ.Upon hearing a siren of a nearby police vehicle, one might think about how this tone is being generated. Similarly, changing the value of the lower value capacitor will change the "blinking rate" of the LED clusters. Increasing its value will increase the time between the successive toggling between the two LED clusters and vice versa. You can change the frequency of "toggling" between the successive LED groups by changing the higher value capacitor. This cycle continues as long as there is power in the circuit creating a cool LED flashing effect similar to the flashing lights used on police cars. Similarly when the first 555 timer IC turns OFF, the second cluster of Blue LEDâs turns ON and blinks at the speed at which the second 555 timer IC oscillates the output. Now, when the first 555 timer IC is ON it turns on the first cluster of Red LEDâs and they blink at the speed at which the second 555 timer IC oscillates the output. Similarly, the second cluster of the Blue LEDâs turn ON only when the output of the first 555 timer IC is OFF and the output of the second 555 timer IC is ON.
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