Control high power LEDs (1W, 3W) from the APM 2.5 LED output

I was looking for a way to make the ARM and GPS LED signals more visible for quite a while. Ideally, I thought, I could drive high-power LEDs somehow from that outputs. A short question in the comments of my blog post with the LED poles didn't yield any results except the reflex-like pointing to the jDrones JDIO board.

Well, I do have a JDIO board and it's not usable for that purpose at all.

Reasons:

  1. The JDIO board is not a LED driver. It's basically just a switch with an Arduino attached. Primary function of a LED driver is to supply a constant current, not to switch stuff on and off
  2. The JDIO board has a current limit of 500mA per channel. That works for 1W LEDs but nor for 3W LEDs.
  3. The JDIO board does decode MAVlink but the (IMHO) most interesting and important infos, i.e. ARM and GPS status, are not evaluated.

So, I started googling and scanning eBay. On eBay I found an interesting assortment of LED drivers from a German supplier - KT-Electronic. I ordered a few drivers and a bunch of other stuff and sent the seller a question about how the driver likes being dimmed by PWM on the supply side. Within a couple of hours I received an email, pointing me to another driver. The email described the circuitry and included the datasheet for the IC that's used on those driver. Actually, the seller has 2 drivers with this chip, one configured to drive 1-3x 1W LED in series and one configured to drive 1x 3W LED.It turned out, that those ICs have a combined analog/PWM input to control the LED output. Analog/PWM combined? Yeah! You can either apply between 0.2 and 5.0V to the ADJ input, which will result to proportional dimming of the output, or send a PWM signal with 0 and 5V amplitude.

This is the module before the modification:

The SN3350 is easily accessible (latter photo, bottom right). All that needs to be done is to solder a servo cable to ADJ (bottom right pin) and GND (bottom center pin) and replace the MR16 pins with some cables. Soldering the cables to the IC requires somewhat of a steady hand but it's totally doable.

This is the module after the modification:

Now you only have to connect the supply line to the battery and the control line to the APM and you have the APM controlling up to (3) 1W high-power LEDs. Don't forget the cooling for the LEDs!

According to the seller, the boards are tested up to 24V supply voltage. The IC can do up to 40 volts but the capacitors are only 25V types. The eBay auction does say 12V for one and 6-16V for the other but that is the normal operating voltage or (in the latter case) the minimum voltage (16V for 3 LEDs). I already tested the modules with a 4S LiPo a couple of hours constant operation and they didn't get noticably hot.

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MR60
Comment by Hugues on June 11, 2013 at 9:59am
Great! Can you post a video in daylight of the leds turned on ?
Comment by Rob_Lefebvre on June 11, 2013 at 10:00am

Cool, thanks!  I actually bought some small/cheap aluminum LED flashlights, you know the type powered by 3 AAA batteries.  I cut off the battery section, so all I have left is the head. I tried running them on 5V, but they burnt out.  I guess I need a driver circuit like this.  

Comment by Acorn on June 11, 2013 at 10:09am

I could be wrong, but, shouldn't the red be on the left and the green be on the right?. . . According to aeronautic/marine regulation for lighting?

Comment by Stefan Gofferje on June 11, 2013 at 10:55am

@Hugues:

That will take a while because the high power LEDs are planned for my next frame. But I guess I can set something up as soon as it stops raining. But take my word for it - 1W LEDs are already nasty, especially with a reflector. 3W LEDs are what's used in warning lights for emergency and utility vehicles...

@Acorn:

There are no regulations at all for LEDs sitting on top of my desk ;).

Comment by Daniel Allen on June 11, 2013 at 11:03am

Thx! Question, are those wires going to the SN3350 acting like an opto IC? Just a simple voltage to switch it on?

Also I wonder if the chinese knockoffs do the same thing. They use different ICs with 8 pins.

Comment by Stefan Gofferje on June 11, 2013 at 11:22am

@Daniel:

Check the datasheet :). 0.2 - 5.0V against ground to the ADJ input proportionally dim the LEDs. That means, as the APM 2.5 outputs 5V against ground on the LED outs, the high-power LEDs flash with full brightness :).

Different ICs have different functions. I also have driver modules for 3x 3W here and those drivers don't have a modulation input.

Comment by Muhammad Al-Rawi on June 11, 2013 at 11:34am

I bought a bag of these off Ebay about a month ago. wonderful and extremely cheap little CC drivers. 

The capacitor is to smooth out AC, since these things are designed to be in little LED spotlights like these in place of these, so the cap can technically be removed. There's a bridge rectifier on there which is also unnecessary. 


Moderator
Comment by David Anders on June 11, 2013 at 3:10pm

Hi Stefan, that's quite cool.  Thanks for the tip about the German supplier.  I usually got mine from a local store here (limited supply) or LEDSupply.com.

I did post something similar back in Jan - http://diydrones.com/profiles/blogs/external-arm-and-gps-led-kit-fo....  It's just a 10mm LED - resistor - APM.  Since, I have put on some headlights for flying at night (limited range) that are also hooked up to the ARMED status, just in case the back isn't facing me.

Do you know how much power your LEDs draw?  And to what distance do yours throw light?  I'm not quite happy with my 'headlights'.  Btw, thanks go to LanMark for the initial spit balling I did with mine. (:

Good work! (:

Comment by Stefan Gofferje on June 11, 2013 at 3:25pm

@David:

Yeah, your blog post got me the first ideas :). From that I made those poles fron the old cat toy. But I wanted more because normal LEDs are hardly visible in sunlight.

I haven't set the LEDs up alltogether yet. When I set them up to take photos/videos in daylight, I can also measure the consumption.

I don't use the LEDs as illumination for FPV or so. I use them as NAV lights, so it's easier to see the copter's orientation from a distance. For illumination, I have 2x 5W LEDs with reflectors flying around. Those are alley-light modules from a police lightbar. Easily 25-30m range. I was also considering trying IR LEDs for illumination. Hobbyking has a 700tvl camera with a huge lens and thus very high sensitivity for around $30. I got one of those. It can see without additional light when I can't see anymore...

Comment by John Githens on June 13, 2013 at 10:05am

@Acorn and Stefan: Months ago I had some fun speculating about red+green lighting for night operations. One approach is as described below. Cheers!

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