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# Police flasher project?

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#### marvel6869

##### New Member
CAN ANY ONE HELP ME I WANT TO BUILD A POLICE LIKE FLASHER THAT FLASHES 3TIME ON LEFT AND 3TIME FLASH ON THE RIGHT?

Here is the circuit you need:

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Here is another one.

I doesn't strobe three times but alternates dual strobes with dual LEDs. (see attachment)

Speed is variable between 10 and 20Hz.

Boncuk

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Boncuk, if you connect the 2 driver transistors to 3 4017 pins (not 2) the lights will be on for 3 periods.

Then add just 2 diodes, each from the 555 output to the base of one driver transistor.

So the 4017 is used for sequencing, and the lights flash at the 555 rate.

Then you get 3 left flashes, followed by 3 right flashes and it only needs 2 diodes more than your circuit.

can i used or how can i convert it from 12v to 9volts? thnk you

if you connect the 2 driver transistors to 3 4017 pins (not 2) the lights will be on for 3 periods.

Then add just 2 diodes, each from the 555 output to the base of one driver transistor.

So the 4017 is used for sequencing, and the lights flash at the 555 rate.

Then you get 3 left flashes, followed by 3 right flashes and it only needs 2 diodes more than your circuit.

It's a little more complex than that as shown in my POLICE LIGHTS project.
You have to take into account the voltage across the gating diode and the minimum voltage on the output of the 555.
See my "50 555 PROJECTS" on Talking Electronics website, for the circuit.

Boncuk, if you connect the 2 driver transistors to 3 4017 pins (not 2) the lights will be on for 3 periods.

Then add just 2 diodes, each from the 555 output to the base of one driver transistor.

So the 4017 is used for sequencing, and the lights flash at the 555 rate.

Then you get 3 left flashes, followed by 3 right flashes and it only needs 2 diodes more than your circuit.

Thanks Mr RB,

the decimal counter needs to be connected for one gap between outputs. Otherwise the connected LED just lights for two clock pulses without interruption. Having one more output pin would solve the problem.

I didn't want to make it more complicated cascading two counters.

Boncuk

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Hi marvel6869,

you can use either circuit for 9V.

Just adapt the LED current limiting resistor values accordingly.

Boncuk

Hi colin55,

I guess neither circuit will flash a pair of LEDs three times alternating. With the values given in your circuit the LEDs flash ten times, while with mine they flash twice.

Boncuk

Colin- does your circuit actually synchonise to exactly 3 beats per light? I think a 4017 solution would be better.

Boncuk- sorry I didn't explain the mod to your circuit very well and I made a mistake.
1. First add 2 diodes so that the 4017 has 6 diodes to the 2 transistors.
This means each led will be on for a period of 3 ticks.
2. Now attach the 555 output through another 2 diodes to the base of each transistor.

Now when the 555 output is low it turns off the transistors. So the leds flash in time to the output of the 555. The 4017 sequences 3 flashes of LEDa and 3 flashes of LEDb.

Colin made a good point about the diodes might not fully turn off the transistors when the 555 output is low. You could get around this in heaps of ways by using FETs, or darlingtons, or schottky diodes, or 2 resistors from base to ground. Also a CMOS 555 might do it too with no other mods.

Here is my circuit to stop all the jumping around with descriptions that don't make any sense.
The point to note here is the fact that you described a circuit without actually building it. I learnt not to try that trick, 40 years ago when I suggested a frequency-to-voltage converter without having actually built it.
No 555 is going to turn off a transistor via a gating diode.
Both of my circuits flash each LED 3 times. You can adjust the dual 555 circuit to produce the exact flash-rate, and effect, you desire.

Hi Mr RB,

I guess you meant it that way.

Timing cap is increased from 100 to 220nF. The rest is unchanged except for four additional diodes.

Power supply is now 9V as desired by the OP. LED forward voltage is assumed 3.5V for a forward current of 20mA.

Boncuk

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This circuit will not work:

No 555 is going to turn off a transistor via a gating diode.

In that case Lab Center's simulation software isn't worth anything.

What else should an NPN transistor do if the base is forced to ground?

Boncuk

Here is my circuit to stop all the jumping around with descriptions that don't make any sense.
The point to note here is the fact that you described a circuit without actually building it. I learnt not to try that trick, 40 years ago when I suggested a frequency-to-voltage converter without having actually built it.
...

That's a bit unfair. The concept I proposed was perfect, I was just rushed and sloppy in describing it.

...
No 555 is going to turn off a transistor via a gating diode.
Both of my circuits flash each LED 3 times. You can adjust the dual 555 circuit to produce the exact flash-rate, and effect, you desire.
...

Now I think you have been sloppy. I proposed a number of working solutions, ie FETs, darlingtons, schottky diodes, with or without CMOS 555 these are all workable ideas and I was deliberately trying to avoid the messy 4 resistor addition that you used (which was my first knee jerk reaction before I thought of better ways).

After a bit of thought, the lowest possible parts count is probably using 2 darlingtons, driven by 6 resistors from 4017 (good idea Colin!), and 2 diodes to turn the darlingtons off.

Boncuk- the last circuit you drew may require schottky diodes, it needs to pull the bases of the transistors below 0.6v to properly turn them off. Also a CMOS 555 might be needed, they are the only type most people buy these days anyway.

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Hi marvel6869,

you can use either circuit for 9V.

Just adapt the LED current limiting resistor values accordingly.

Boncuk

Many Thanks

CAN ANY ONE HELP ME I WANT TO BUILD A POLICE LIKE FLASHER THAT FLASHES 3TIME ON LEFT AND 3TIME FLASH ON THE RIGHT?

The simplest way, interms of component count, is to use a PIC. Something like a 12F6xx series 8 pin pic will do the job nicely..

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This circuit will not work:

That's a statement without prove.

Well, it works perfectly in the simulation. Take a look at the screenshots. The base voltage is well below 0.7V when the timer output goes low.

What makes you sure it won't work?

Boncuk

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In my cirucit, you will see I have a voltage divider on the base of each transistor to turn it off.
Without the voltage divider, the transistor will not turn off.
Is that enough proof?
Why don't you actually build the circuit and prove it will work, before putting it on the web?

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i just want more simple circuit and also work as flasher.....

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