Emergency Flashers

Introduction: Emergency Flashers

This Instructable is about the evolution of a circuit and its construction in it I will be covering three things I see little mention of in circuits on the net. Building on an idea, optocoupling, and circuit isolation. Although optocoupling and circuit isolation are the same things circuit isolation can be achieved with diodes as optocoupling uses light and through fiber optics can be achieved over great distances and power differentials.

An Instructables member wanted to make emergency flashers for his truck out of Luxeon Star high powered LED lights or something like them. He wanted the lights to flash left, right, left, right, and if he could get them to stay on when he wanted them to. So the first thing I did was to go to Luxeon Stars website and down loaded the datasheets on their high powered LEDs and drivers. 

I came up with a simple 555 timer clock to a JK Flip Flop controller to flash the LEDs left to right and back. I chose the 555 timer because it is the easiest multivibrator to get and use by novices but any multivibrator will do.

Step 1: The First Circuit Evolution

It wasn’t long after starting and I realized the circuit would need a voltage regulator for the JK Flip Flop, 12 volts is fine for the 555 timer however the JK Flip Flops I have in stock run on 5 volts.

To the circuit I added an on indicator LED, LM7805 voltage regulator and high speed diodes to isolate and protect the circuit from power surges and feedback.

Step 2: The First Prototype

In the first test prototype I skipped the on Indicator LED and the on switch and after numerous calculations came up with values for the resistors and capacitors to be tested. A switch to turn on the LEDs without flashing was impractical so I came up with speeding up the flashing until the LEDs look like they are on all the time so I added a 50 k Ω pot to the 555 timer circuit. This circuit will function as desired whether it is connected power through LEDs to JK flip flop or flip flop to diode to ground.

Step 3: Parts

The 1N4001 diodes, LM7805 voltage regulator, and the NE555 timer can be found at Radio Shack or you can get them and the other ICs on line I get my ICs at Mouser Electronics and found them to be good to deal with.


1 - LM7805             voltage regulator
1 - NE555                timer
1 - SN74LS73A        JK Flip Flop
2 – FR151                diodes
2 – 2N3906             transistors

You can get the diode and IC datasheets at:




From your local Radio Shack or on line electronics store get:

1 – breadboard for testing
1 – protoboard
1 – switch
1 – Green LED
1 – 50k ohm pot (Variable Resistor)
2 – 150 ohm ¼ watt resistors
3 – 1k ohm ¼ watt resistors
1 – 220uF 16 volt electrolytic capacitor
1 – 4.7uF 16 volt electrolytic capacitor
2 – 1uF 16 Volt electrolytic capacitors
And lots of wire

I always get extras just in case I need them.

Step 4: Then Test the Circuit.

I assembled the circuit on a breadboard and test all its functions and driving circuits, you can add a transistor to the LED circuit the addition of a 2N3906 can boost the output from 50 milliamps to 200 milliamps to drive more LEDS, for driving circuits above 200 milliamps I like to use optocouplers to connect circuits of different powers.

I included drawings of the components for novices in electronics to make things easier for them to construct the circuit themselves.

Step 5: Optocouplers

Optocouplers are an LED on one side and a phototransistor on the other side; optocouplers allow the transmission of a signal from a low powered circuit to a high powered circuit using light to transmit the signal. Optocouplers and fiber optics enable sensitive electronic control circuits to operate and receive data from circuits a thousand times more powerful without expensive transitional circuitry and with little chance of feedback or power surges damaging the signal circuit.

Optocouplers come in analog and digital ICs packages consisting of 1, 2, 3, and 4 couplers and a variety of voltages and powers.

Step 6: The Finished Left Right Flasher

The next step is to connect this circuit to the Luxeon Star high powered LED driver. With circuits of different voltages current and power I like to isolate them with diodes and optic isolators to prevent power feedback that can damage the lower power circuit, so I added three Isolating diodes and two optocouplers.

The Luxeon Star LED driver to use with this circuit is the six wires dimmable driver for strobe function you connect a 2N3904 transistor collector to Dim wire and emitter to dim ground wire and base to in coming signal.

For this function I replaced the 2N3904 with an optocoupler capable of carrying the same current, now the signals are carried by light and there is little chance of feedback or power surges damaging the signal circuit from the Luxeon Star LED driver.

To the parts list add K815P optocoupler, can be purchased at Mouser.



Step 7: Luxeon Star High Power LEDs

Luxeon Star has manuals, datasheets, and how to videos, available on line at:


The datasheets and videos take you through the construction of the high powered LEDs and wiring the LED drivers. For flashers you need the dimmable LED drivers connected for strobe as shown in these picks.

Step 8: Stepping Things Up One

I hate not using all of an IC and just using one JK Flip Flop in an IC with two Flip Flops irks me besides I can make the flasher do something different, I can make it flash Right, Right, Left, Left, and back with the addition of And gates.

To the parts list add a 100k ohm pot, a K845P optocoupler, and SN74LS08 And gate, both And gate and optocoupler can be purchased at Mouser.


Send the 555 timer clock pulse to the first JK Flip Flop and one side of all four of the two input And gates. From the first JK Flip Flop connect the Q to the second Flip Flops clock. From the second Flip Flop connect Q to two of the And gates second input and the Q to the other two And gates second input. Connect the set of the JK Flip Flops to the 5 volt power now when you connect the LEDs up to the And gates the same way as in the Left Right Flasher, they flash Right, Right, Left, Left, and back.

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    3 Discussions


    5 years ago on Introduction

    Going back to the original circuit requirements, "to flash left, right, left, right" why do you need a 74LS73 ? You could have achieved this just with the 555 and then would not have to use the 7805 and all of it's associated components. Then just add op transistors to drive the Luxeon Stars.

    Josehf Murchison
    Josehf Murchison

    Reply 5 years ago on Introduction

    Clean square wave 50/50 and the second JK plus an and gate you can flash twice on one then flash twice on the other.