A tutorial on how to make a Police Lights themed LED Flashing/Blinking LED circuit using 555 timer IC and a few other electronics components. This circuits alternatively flashes between Red LED’s and Blue LED’s while blinking each of them individually similar to police strobe lights. Explanation of how this circuit works is also included in the video tutorial.
You can also club this circuit with police siren circuit, which is the next project in this 555 timer projects series: Police Siren Circuit Using 555 IC.
- 2 x 555 Timer ICs
- LED’s: 3 x Red, 3 x Blue
- Resistors: 2 x 1M, 2 x 68R (Resistors for LED’s)
- Capacitors: 1uF, 100nF
- Few Breadboard Connectors
- (5-12)V Power Supply
Note: Depending on the power supply used and the way LEDs are connected (series or parallel) you need to use a different resistor than 68R used in series with the LED’s. Refer to the table shown in the video tutorial above for resistor to be used for basic scenarios. You may also visit http://ledcalc.com/ to calculate the resistor based on LED arrangements.
How This Circuit Works
[Do watch the explanation given in the video tutorial for better visual understanding]
In a previous tutorial: Adjustable Flashing/Blinking LED Circuit using 555 Timer IC, we learned how to configure 555 timer IC to operate in astable mode. We also connected 2 LED’s in opposite polarity at the output so that they toggle ON and OFF at regular intervals of time. You may refer to that tutorial to understand the working of 555 timer IC in astable mode and how the values of capacitor and resistor influence the flashing rate.
In this police strobe lights style flashing LED circuit, we have used two copies of similar astable circuits configured at different frequencies. The first 555 timer IC, uses a bigger capacitor and so it takes more time to toggle the output. The second 555 timer IC uses a smaller capacitor and so it toggles the output very fast.
Now coming to the arrangement of LED’s, The first LED group (Red LED’s) turns ON when there is positive voltage at the anode and negative voltage at the cathode. This scenario happens when the output of first 555 timer IC is ON and the output of second 555 timer IC is OFF at the same time.
Similarly, the second group of LED’s (Blue LED’s) turn ON only if the output of the first 555 timer IC is OFF and the output of second 555 timer IC is ON.
So when the output of the first 555 timer IC is ON, only the first group of LED’s have a chance of turning ON and they blink at the speed with which the second 555 timer IC toggles the output.
Similarly when the first 555 timer IC turns OFF, only the second group of LED’s have a chance of turning ON and they blink at the speed with which the second 555 time IC toggles the output.
Repetition of this cycle again and again creates this cool LED flasher effect similar to flashing lights used on police cars.
If you have any queries/suggestions, feel free to post them in the comments section of this video: Police Lights Themed Flashing LED Circuit Using 555 IC