555 Based Flash Contoller with Alternating Flash Rates

Thread Starter

Bronxville Tech

Joined Mar 30, 2012
Anyone have any links to a schematic that allows for a 555 (or 556) based controller that can drive a 36V/100W LED with alternating flash rates?

Here's where I'm looking to go eventually:

1. Strobe circuit allowing for 36v in and 36v out, DC.

2. Pulse rate flips from 9hz to 15hz every second.

3. Support for up to 4A

4. Latch timer. Trim pot to adjust "on" timer from 1 second to 10 seconds.

5. Heat not an issue. Unit will not be run for excessive cycles.

6. Fit in to smallest RS style project box.

7. Running from (6) 6V batteries so V regulation for sensitive lamps might be an issue.


Joined Sep 9, 2010
That change in frequency is small enough that you could use the control pin 5 to make the shift. Just use one half of a 556 at 1 Hz with the output sent thru a resistor to the control pin of the 2nd half. Roughly, the 2nd timer would be set to 12 Hz but would only operate at the two extremes when the control pin is Hi or Lo. You'll need to work out the math, or experiment around, to choose the right resistor values and get it all right.

You may want to search for "police siren" circuits, as that's what they do, shift between two frequencies.

You'll need a logic MOSFET to drive your LEDs from the 6v timer output.


Joined Mar 24, 2008
I will get back with you, right now I'm tired.

The post you put in Looking for Specialty Light Circuit is a hijack. A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits.

Since you already have this thread I'll just moderate (render invisible) the other one.

You mention 9V power supply, I assume it is not automotive? If it is please read our Terms of Service.


Joined Mar 24, 2008
Couple of side comments. Heat is always an issue, those who fail to plan for it will buy new parts. Things will get very toasty on the LEDs in under a second. 100W of electrical power for LEDs will be much brighter than a 100W light bulb, as LEDs are more efficient, but LEDs also get hot.

Raw LEDs do not drop 36V. Color matters, the amount of voltage a LED drops is dependent on it.

A white LED that is rated 100W is going to pull around 28A. If you have a bank of LEDs at 36VDC it will pull around 4A, as you mentioned.

What the above basically says is you are going to have to look up the LED for the datasheet. Their is a good chance you will have to use multiple LEDs.

Before we can begin to help, you will have to provide the LEDs specs you plan on using, this means a seller and datasheet, and probably a partial schematic.

The frequency shift is also a bit confusing, and will need defined a bit better.

You said alternating LEDs, so let us call bank 0 blue, and bank 1 red.

You are wanting this pattern?

<1 second @ 9Hz><flash><flash><flash><flash><flash><flash><flash><flash>

<1 second @ 15 Hz>