The BLUE LED’s also will be ON for 100ms and for three times. Since Q5, Q7, Q9 are so connected to drive the BLUE pair. Q1-LED off for 100ms, as Q1 high every other output will be LOW, and Q1 is not connected to drive RED pair.īy the next clock Q5 will be high and all others will be low. Since Q0, Q2, Q4 are controls of RED pair, they will be ON for 100ms, three times as: As the overflow of count takes place, the counter resets itself and starts from zero again. The first transistor drives a pair of RED LED’s and second transistor drives a set of BLUE LED’s.Īs said earlier, the counter output gets incremented by one for every 100ms until the over flow. Here Q0, Q2, Q4 are connected to base of one transistor and Q5, Q7, Q9 are connected to another transistor base. Now the decade binary counter counts the number of pulses given at the clock and lets the corresponding pin output go high, for example, if the event count is 3 then Q2 pin of counter will be high and if 5 is count the pin Q4 will be high. So for every 100ms there will be a peak, with this peak the counter memory gains by one and so is the output. These pulses are fed to the DECADE BINARY COUNTER. This time duration can be changed by changing the value of capacitor. So the ON time is 50ms and OFF time is 50ms. The above figure shows the circuit diagram for poice lights. The timer here generates pulses of time period 100ms approximately.

RED LED (2 pieces) and BLUE LED (2 pieces) The timer here generates pulses which are fed to the 10-stage decade counter, the output of counter is so arranged to get a flashy lights as a police car.ġ0♟ capacitor, 100♟ capacitor (not a compulsory, connected in parallel to power). Circuit diagram with Parts list.In this project we are going to design a circuit, to make a flashing light similar to that on a police car. This police light circuit is designed by 555 Timer IC and a decade counter IC. When the capacitor C1 is charged the tone will rise and when the capacitor C1 is discharging the tone will fall. Then the capacitor C2 discharges, and transistor Q1 will be switched ON again to start a new cycle. This action continues until both transistors become OFF. As a result the collector voltage of Q1 drops and makes the Q2 more OFF. This results in an increase in the collector-emitter voltage of Q2.This change in voltage is coupled to the base of Q1 via the capacitor C2.As a result the transistor Q1 comes slightly out of saturation. The capacitor C2 will be charged almost to full supply voltage.

When the Q1 is switched ON, its collector voltage falls and makes the transistor Q2 ON. When the switch S1 is released the C1 will discharge and the transistor Q1 will become OFF slowly. When you press the push button switch S2 capacitor C1 will charge and this will make the transistor Q1 to ON slowly. The circuit given here produces an alarm similar to the police siren.

Police light ne555