Introduction: 20W LED-strobe for RC-aircraft

This is my very first instructable, and keep in mind that English is not my native language. When that said, the idea was to create a strong strobe light with minimum weight and power consumption for use on my homemade, radiocontrolled multirotor drones (Ardupilot of course ;) ). When flying at higher altitudes and/or longer distances, it's difficult to have good visual contact with the aircraft. So I thought a flashing high-powered light would help me see it even when it's far away. In "old days" we used xenon flash tubes w/high voltage circuitry to accomplish strong flashes. Many kilowatts in a few microseconds can be substituted by watts in milliseconds, giving the human eye the same impression of light. Today we have high powered LEDs on the market for a very reasonable price. This is how to make a 20W pulse LED-strobe working at voltages between 11 - 16 volts DC (3S - 4S lipo), in a compact and lightweight package.

Edit: NOTE: Some Chinese clones of the Pro Mini will burn at 12V and more, as the internal 5V regulator doesn't accept input voltages above 12V. To solve this I recommend a 4.7v zener diode in series with the +V from battery to the "raw" input on the Arduino. Remember that zener diodes should be connected in the opposite direction; e.g. the cathode (marked with a ring) against the battery side. Other alternative is to use a cheap 7805 voltage regulator, and power the Arduino with +5V into the "Vcc" (not "raw").

Step 1: What You Need From EBay (or Other Source):

2 pcs. 10W cool white LEDs (approx. USD 3 for both - be sure it's the 9-12V/900mA version)

1 pcs. Arduino pro mini clone, 5V/16MHz (approx. USD 2)

1 pcs. IRF540N MOSFET transistor (You can buy 10 for less than USD 3)

Some wires and (optional) transparent heat-shrink tube, 20 mm with before shrinking

Step 2: Programming the Arduino Clone

You should first program the arduino, or else (like me) end up in the end soldering Tx/Rx lines on the finished strobe. How to program the Arduino is not explained as I presume you know how to do this. The code will follow with explanation in the end of this instructable. If you like, you may also solder some header pins to GND, Tx and Rx for later modificatons of the software. It's up to you. My goal was to keep the weight to a minimum.

Step 3: Assembling the Parts:

On the backside (no components side) of the Arduino I've sticked som double-sided tape, and fixed the two LEDs onto the Arduino as pictured. Remember to fix the LEDs so they have the same polarity on each side. The heat sink on the LEDs is not conducting any current nor connected to the anode or cathode on the LEDs.

Step 4: Solder LEDs Together:

Use some wire to connect the two LEDs together; anode to anode and cathode to cathode. Or the easy explanation: + to + and - to -. You can trim the edges of the LED's connectors, so that it will be a smaller footprint on the final build.

Step 5: Gluing the MOSFET

I've used fast dry superglue to mount the MOSFET as pictured on the backside of one LED. Also I've cut most part of the legs,

Now it's time to solder it all together. The legs on the MOSFET is as pictured (seen from left to right on the heatsink side): 1 - drain, 2 - source and 3 - gate.

* The "minus" (-) side of the LEDs should be connected to source (leg in the middle) on the MOSFET

* The "plus" (+) side of the LEDs should be connected to "raw" on the Arduino (not Vcc), and also the +12V power wire from the battery/power source

* The ground wire (minus wire from 12V power) should be connected to GND on the Arduino, and to leftmost leg at the MOSFET (drain).

* Finally, the gate on the MOSFET (rightmost leg on the pictures) should be connected directly to pin 13 on th Arduino with a short wire.

If you want, you can pack it all in a transparent shrink-tube to protect the circuit from rain and dirt when installed on the drone/aircraft. With approximately only 15 grams of mass, the finished product is very lightweight for it's use.

You may change the code yourself of course, but be aware that if the duty-cycle of the LEDs is to high, they will get very hot and probably damaged. In this code there is a total of 1240 mS (milliseconds) for one cycle, in which the LEDs are turned on only 40 mS. This gives us 40/1240 * 20 = 0.65 watts average power consumption, even when the LEDs are flashing at full 20W power in pulses. They will not get hot at this average level. This is also good news for the aircraft's battery in respect of flight time.

NOTE (!!!!):
The battery power shall to the "raw" connector on the Arduino, NOT the "Vcc".
The Pro mini (and it's 5V clones) have a built-in voltage regulator which accepts voltages up to 16V or more, and regulates the voltage down to 5V internally on the board. This is important - if you confuse the "raw" input with the "Vcc", you WILL damage your Arduino.

Step 6: Code and a Short Video

Practical tests have shown that the strobe is clearly visible at least 400 ft (120 meters) away on a clear, sunny day. In darker conditions the strobe will, of course, be visible at much longer distances.
Enjoy the project!

Step 7:


NishadhK made it!(author)2017-07-09

does it use for bike 12v battery?

is it harmful or not ?

einyaa made it!(author)2017-07-09

It will work very well.

AirS3 made it!(author)2016-03-10

what makes the led flash 3 times? is it the mosfet or arduino?

einyaa made it!(author)2016-03-10

It's the arduino counting, the mosfet flashing ;)

AirS3 made it!(author)2016-03-10

ty.. can i use these things using 12v power? how?

einyaa made it!(author)2016-04-19

You should consider to follow this instructable with the Arduino pro mini. I can't assist you in building with another parts, as the attiny. But it is possible to use this MCU if you can program it.

Jean0x7BE made it!(author)2016-04-13

Very nice indeed - will definitely make this!

einyaa made it!(author)2016-04-19

Cool :)

synespro made it!(author)2016-04-15

Thank you SO SO much! I have had so much fun with this! Thank you~

I have come to a challenge that i could not overcome and could not find any leads from my own research. I wondered if you can help: When I have light (10w LED) Turning on doing the digital strobing, there is a start up flicker , as if the power is ramping up. This messes up the frequency. When turning off it is a clean OFF. Do you have any ideas why this is the case, and how to remedy it? I am using the final diagram i made earlier with the voltage regulator, and transistor, arduino, and led. Thanks a million!

einyaa made it!(author)2016-04-19

Hi and thank you for your nice comment :). My first thought when reading about your problem is voltage drop. When the LED turns on, the circuit conducts much more current than when it's off. This may cause a voltage drop; the LED is not powered with enough current and the voltage drop may interfere with the arduino's stability. If so, solder an electrolytic capacitor (e.g. 100µF/10V) on the + and - wires on the arduino board, and be sure you have wires with sufficient cross-sectional area. As an example AWG16 should be fine.

Another issue "may" be some oscillations in the MOSFET. Try a resistor on 100 ohm between the gate and the arduino, instead of direct connection. Hope this may help you out! Also solder a ceramic 100pF capacitor between gate and source.

The third issue is your power supply. Do you use a switchmode power supply for your strobe? In that case it may be the supply itself not beeing able to deliver a steady voltage when sudden changes in current occur. Try another supply.


synespro made it!(author)2016-01-18

Thank you for this. If I wanted to use this on the ground, and use brighter lights, like 50w or 100w LEDs , How can do that? What would be the right MOSFET? Thank you so much

einyaa made it!(author)2016-04-19

Hi. The problem with higher powered LEDs than 10W is that they require a higher working voltage than 12V. If you know how to do it (power the arduino with less than 12V at "raw" or regulated 5V to the "Vin"), it should be no problem. The MOSFET I suggest can handle up to 60 volts and 33 amps. Another way to do this is to use several 10W LEDs in parallel in a 12V system. As they use about 1A or less each, you can use up to 20-25 x 10W LED in this construction. For higher currents you can connect two or more MOSFETs in parallel too (pin 1 to 1, 2 to 2, 3 to 3). I suggest max. 3 MOSFETs directly from the arduino. If more I would use some kind of buffer between the arduino output and the gates on the FETs.

So if you can use 10 pcs of 10W LEDs to accomplish your goal, then you can do so without any changes in the rest of the circuit, except probably also use an electrolytic capacitor (470µF/16V) between the GND and RAW on the ardino (+ to RAW), to avoid resetting at higher power surges. Good luck!

GunnarN1 made it!(author)2016-01-28

Thanks for this. Finally made me delve into the Arduino world.
Having fun programming interesting Strobe-Patterns now..

By the way, there's a lot of fake 2303 USB to Serial-chips out there, which won't work with Prolifics new drivers, which sense the copied chips.

Their old drivers still seems to work on Windows 10 though.

In a thread discussing this, I found v. of the Windows 7 drivers. You can get it from here:

einyaa made it!(author)2016-01-29

Thanks for nice comment! I'm glad you made it and for the tip of 2303HX-drivers for Windows 10.

synespro made it!(author)2016-01-19

Thank you that helps alot! I have an arduino Nano. I was thinking of powering the Nano with its usb power from a plug, and use a heatsink with the Led. Does this image look like it would work? I really appreciate your help. Thank you. I am inspired to run several LEDs in parallel in the future, per your suggestion.

einyaa made it!(author)2016-01-19

You have connected the MOSFET correct in the picture, but confused D and S. Also connect a wire between source (S - pin 3)) on the FET to GND on the Nano. Then it should work ;)

1=Gate, 2=Drain, 3=Source (from left to right, when looking at the FET's front).

1: Gate to Arduino, 2; Drain to LED, 3: Source to GND

synespro made it!(author)2016-01-20

I Think Ive almost got it. I appreciate your attention. I made an
updated graphic to save us both time. I had the Transistor facing
backwards. Is this correct? Thanks in advance!

synespro made it!(author)2016-01-20

I made that picture from your original instructions indicating:

"* The ground wire (minus wire from 12V power) should be
connected to GND on the Arduino, and to leftmost leg at the MOSFET

synespro made it!(author)2016-01-20

I did some research, And i believe this is the right setup

einyaa made it!(author)2016-01-20

Yes. This will work :) Good luck on your project!

Source must be common GND. Drain to LED.

If this is a high power system, I would probably (just in case) use a 1000 ohm resistor between the Gate and D13. And a 470µF capacitor on the nano between Vcc and GND. Just to protect the Nano from going into reset/beeing disturbed by the high current pulses in your setup. But it will probably work fine as it is in your schematic.

synespro made it!(author)2016-01-20

Thank you! I would not have thought to add the resistor and the capacitor for protection. The arduino Nano does not have a Vcc pin. What would you suggest?

einyaa made it!(author)2016-01-21

You may use "5V" instead of Vcc. This should work good regardless if powered via "Vin" (7-12V) or by the USB (5V).

synespro made it!(author)2016-01-19

Sorry i am but a humble man and confused.
When you said

* The ground wire (minus wire from 12V power) should be connected to GND
on the Arduino, and to leftmost leg at the MOSFET (drain)."


* Then connect a wire between source (S) on the FET to GND on the Nano.

Which one is correct?

oliveira.igorm made it!(author)2015-12-07

Cool mod for a drone. Looking foward to seeing a video of it on field!

einyaa made it!(author)2015-12-11

As you wish :)

oliveira.igorm made it!(author)2015-12-11

Thanks! It works really well!

nyffeler made it!(author)2015-12-11

Can you tell us the type and manufacturer of the LEDs you are using?

einyaa made it!(author)2015-12-11

Only search for 10W LED on eBay. Be sure it's the 9-12V version.

seb0p made it!(author)2015-12-09

Nice. I was looking for that. But how did you programm the Pro Mini clone? There is no usb port or else on this thing.

einyaa made it!(author)2015-12-09

I use a PL2303HX USB to TTL -adapter and connect GND to GND, Vcc to Vcc from the adapter to the mini. Adapter Tx goes to Rx on the mini, and Adapter Rx to the mini's Tx. Just when the IDE is starting to upload the compiled code, press "reset" on the mini for a second. Or you can use a FTDI-adapter (which resets the mini automatically when uploading).

Another approach is to use an Arduino Nano, which is a mini with an USB-adapter integrated on the board. But this one is a little bit larger than the pro mini.
Or you can try this:

Yonatan24 made it!(author)2015-12-08

You should add it in to the Instructable if you think it's important, Not everyone looks at the comment section

einyaa made it!(author)2015-12-08

Thanks. I just did. I'm new to this and edited it now.

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