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

Posted by Stefan Gofferje on June 11, 2013 at 9:00am

FILE0038.jpgI 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:

FILE0037.jpgFILE0036.jpgThe 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:

FILE0035.jpgNow 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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Comments

  • gustavo March 25, 2014 at 4:27pm

    Thanks for your answer, 

    Being so , i will first use analog out to control the leds and in the future do something with an arduino nano.

    Rgds

    Gustavo

  • Muhammad Al-Rawi March 24, 2014 at 1:06pm

    Assuming you're talking about R/C PWM, it can not be turned off, as the pulse width does not go to zero. RC signals go from 1-2ms, like so, and never actually send out a solid zero. What you're looking for is PWM like you'd get using the analogWrite() in Arduino, seen here.

    You can use a small micro-controller like an ATTINY13 or 85 to take your RC signal and output PWM. I've been thinking about doing this to control my nav lights and strobes.

    You may even be able to do it with some sort of resistor-capacitor network. 

    Assuming you're talking about real PWM, I have no idea. It seemed to work well back when I tried it. I just had a resistor between the PWM from my Arduino and the pin on the IC. 

  • gustavo March 24, 2014 at 9:56am

    When i connect the adj input to a pwm output, it works but is impossible to turn it totally off.

    Any modifications to do in order to get it fully working? 

  • Stefan Gofferje September 1, 2013 at 4:48pm

    Both. I have one for GPS and one for ARM.

  • Cam Batten September 1, 2013 at 4:33pm

    great, I've ordered a couple of these chips, any build tips in hindsight? Were you using Motor or GPS arm signal's to trigger anything from the apm unit?

  • Stefan Gofferje September 1, 2013 at 4:20pm

    Yeah, and ripped it apart and rebuilt it 2 or 3 times :D. From the LED side, everything works fine.

  • Cam Batten September 1, 2013 at 4:17pm

    Did you end up completing this build Stefan? Everything work out as you expected?

  • Muhammad Al-Rawi June 15, 2013 at 9:23pm

    The ones I have run on a ZXLD1360, which also takes PWM. 

    Page 14 notes driving via microcontroller. 

  • Stefan Gofferje June 15, 2013 at 9:04pm

    @Jason:

    The ones on dx.com are using a different driver chip! Check the photos! Physically, most LED drivers look similar, because they are all meant to be built into a small housing together with the LED and some optics. However, only the SN3350 so far has a modulation input.

  • Jason Wise June 15, 2013 at 5:09pm

    Also here is a awesome list of LED's/Drivers

    http://www.videofoundry.co.nz/ianman/laboratory/research/driverlist...

    Aqualab: LED Driver List - LED Drivers and Regulator Boards (database driven)
This reply was deleted.