Looking around in past post but not really seeing what I want…

looking for the simplest 2 LED strobe that alternates back and forth flashing twice each. Runs at 9vdc. Example Left LED, quick flashes twice then the Right, LED quick flashes twice and repeat until powered off.
I don’t have time duration but I think most of us have seen something similar in the grill of a police car or on a construction vehicle, even on some mail delivery vehicles. Again nothing fancy. ICs are ok but not wanting to program anything…
Thank You

 

Maybe use the trusty old 555 as an astable to trigger a 4017 decade counter with Q0 connected to an LED via a resistor to ground, Q1 left unused, Q2 to the same LED, Q3 unused, Q4 to the other LED and so on. Q8 connected to the reset pin. This should turn the LEDs on with a 50/50 mark space ratio

There are examples of the 555 with the 4017 to make an “LED Chaser” on the web which can be adapted as above

 

Maybe use the trusty old 555 as an astable to trigger a 4017 decade counter with Q0 connected to an LED via a resistor to ground, Q1 left unused, Q2 to the same LED, Q3 unused, Q4 to the other LED and so on. Q8 connected to the reset pin. This should turn the LEDs on with a 50/50 mark space ratio

There are examples of the 555 with the 4017 to make an “LED Chaser” on the web which can be adapted as above

Thank You. I have seen these. I’ll check it out

 

Looking around in past post but not really seeing what I want…

looking for the simplest 2 LED strobe that alternates back and forth flashing twice each. Runs at 9vdc. Example Left LED, quick flashes twice then the Right, LED quick flashes twice and repeat until powered off.
I don’t have time duration but I think most of us have seen something similar in the grill of a police car or on a construction vehicle, even on some mail delivery vehicles. Again nothing fancy. ICs are ok but not wanting to program anything…
Thank You

Does this need to be a "triggered" circuit or begins flashing at power on?

 

[broken record mode]
An 8 pin micro can do it with just 1 capacitor, two resistors, and the two LEDs.
[/broken record mode]

 

[broken record mode]
An 8 pin micro can do it with just 1 capacitor, two resistors, and the two LEDs.
[/broken record mode]

Don't forget the regulator if the source happens to be above 5 Volts.

OP says 9 Volts.

 

Does this need to be a "triggered" circuit or begins flashing at power on?

Just begins strobing on power on, ends at off.

 

Just begins strobing on power on, ends at off.

A simple effect. Power on ( left led flash-flash then right led flash flash) repeat

 

A simple effect. Power on ( left led flash-flash then right led flash flash) repeat

You could use a dual 555 timer and a couple transistors. One timer to do the double flash, and the other to alternate between the left and right LEDs.

 

Don't forget the regulator if the source happens to be above 5 Volts.

OP says 9 Volts.

PIC has some with built in shunt regulator, so one more resistor.

 

You could use a dual 555 timer and a couple transistors. One timer to do the double flash, and the other to alternate between the left and right LEDs.

I’ll have to look into how to do that. Thank you!

 

I’ll have to look into how to do that. Thank you!

Alternate and flash aren't synchronized, but it doesn't sound like you want the added complexity of doing that.

 

View attachment 318655
Alternate and flash aren't synchronized, but it doesn't sound like you want the added complexity of doing that.

Oh My… your sources of circuits must be vast. Very kind of you to share this circuit. The values of resistors/capacitors critical? I can experiment…..

 

your sources of circuits must be vast. Very kind of you to share this circuit.

I drew it from scratch.

The values of resistors/capacitors critical? I can experiment…..

Depends on the alternate and flash rates you want. You can use this nomogram from National Semiconductor to estimate values. Or you can do the calculations from the datasheet.

If you make RB much much larger than RA, you'll get about a 50% duty cycle.

 

Yeah OK. I’m trying to simulate the front grill strobes in this video….ah guess I can’t attach a video

Here is a link:
https://www.facebook.com/share/r/ZwSYmVmWHsVnr64C/?mibextid=UalRPS

 

Yeah OK. I’m trying to simulate the front grill strobes in this video….ah guess I can’t attach a video

What are the flash and alternate rates?

 

If you din’t want to go with the micro, the 555 and 4017 solution is much better.

 

If you din’t want to go with the micro, the 555 and 4017 solution is much better.

I have built flashers with these ICs so I think I’ll breadboard this up. I think I can figure this out

 

If you din’t want to go with the micro, the 555 and 4017 solution is much better.

Thinking about connecting two outputs of the 4017 to one LED makes me wonder if it’s okay to effectively connect two outputs together. Maybe, instead of connecting the LED directly (with one current limiting resistor to ground) the outputs should be connected to the LED via a resistor at each output, or maybe a diode for each output and one resistor from the LED to ground.

Perhaps someone could say if this is necessary, I’d probably use diodes to protect the 4017 just in case!

 

It will take two CMOS ICs and some high gain transistors. two hex inverters for a one device pulse generator, (CD4049) then a CD4017, with outputs "0" and "2" triggering one transistor to light one LED for two flashes, then outputs "5" and "6" triggering the other transistor to flash the other LED. Two buffers diode-OR'ed for the two quick flashes. And run it all on 9 volts with a resistor that allows more that the 20 mA because the flashes are short.
The LEDs can handle a fair amount more for shorter time periods. The transistors can be MPSA12 or 13 so that they can switch on fully with a CMOS direct drive. And it could be only one current limiting resistor because only one LED at a time will be lit. Or a resistor for each color if different colors are used.