The main concept of "Police Light " circuit !

Hi everyone ..
I'm a new member her
and I just have finished the police lights circuit , and it works perfectly

but !

I really wanna understand how it works like this .. I've read some information about 555timer and the 4017B IC .. and I'm kind getting their purpose but I need someone to explain the main Idea of this circuit and why we need the transistors here in just a few words

I really need your help

thank you

Jan

View attachment 64144

In layman terms:

The 555 works as a clock or metronome and sends pulses from time to time via his leg # 3. The pulse interval is determined by the capacitors and resistors connected to the other legs.

Every time the 4017 sees a pulse coming from the 555 it turns off the output pin that is active at the moment and turns on the next one (they are numbered from zero to nine). When the count reaches more than nine the 4017 just returns to leg zero and start over again.

The 4017 doesn't have enough "strength" (doesn't provide enough current) to drive 4 LED at the same time with one output, so it drives a transistor instead.

The transistor acts like a wall switch, turning the load on or off according to the voltage received on his Base Leg (that's the one in the middle). If voltage goes high the transistor closes the circuit and the corresponding LED group shines.

now it's getting clear
but why each transistor's base is connecting with three diodes

and thank you for your reply

As you can see pins 0, 2 and 4 are connected to the same point. The same occurs with pins 5,7 and 9.

The diodes allow each pin to power the correspondent transistor but not the pins in the neighborhood.

Your are Welcome

are they used for make each 2 LEDs flash 3 times within a second !

uh that's right ^.^

thaank you very much my friend
I really appreciate your help

Jan De said:

are they used for make each 2 LEDs flash 3 times within a second !

Click to expand...

No. That happens because pin 0 is connected to the (let's say) the red LEDs. When Pin 2 goes high it's also the turn for the red LED. Then Pin 4, again the red.

The same occurs with 5, 7 and 9 and the blue LEDs. That's why you see "three reds - three blue - three reds - three blue - etc.

Good luck pal!

All the 555 circuits have been copied from my site. He has used an old Police Lights circuit and he has made a couple of mistakes. The 4k7 current limiters for the LEDs should be 470R.
The circuit can be made much simpler by using 470R resistors for the gating:
View attachment 64149

Menticol said:

No. That happens because pin 0 is connected to the (let's say) the red LEDs. When Pin 2 goes high its also the turn for the red LED. Pin 4 again the red.

The same occurs with 5, 7 and 9 and the blue LEDs. That's why you see "three reds - three blue - three reds - three blue - etc.

Good luck pal!

Click to expand...

this is actually what I mean , but you say it in a professional way
it's completely clear now

colin55 said:

All the 555 circuits have been copied from my site. He has used an old Police Lights circuit and he has made a couple of mistakes. The 4k7 current limiters for the LEDs should be 470R.
The circuit can be made much simpler by using 470R resistors for the gating:
View attachment 64149

Click to expand...

you're right the new one doesn't have diodes and it looks simpler
but the LED resistors will not make different if I change it to 470 right ?

I did a uC version the other day (12F675) which makes it easy to do the quick triple flash on each colour while oscillating between the colors (red & blue in my case). Yes a uC is a bit of overkill but I could alter the behaviour with firmware which i prefer.