» MAKE: NOISE — Discuss this article

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• troubleshooting...
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  I tried building this over the weekend with parts from mouser, straight from the list in the article, but with a few substitutions (the LED is 3.7v instead of 3.5) and I used a regular diode for the battery part, because the Shottky diode Mouser send is huge and looks nothing like the one in the magazine article.
  
  It doesn't work.
  
  I have de-soldered everything and re-assembled with a fresh transistor, in case I cooked the original. I swapped the 1K resistor for a 2.2K. I tried hooking up an AA battery to + and - to see if it was not getting any power. The LED works fine if you put 3+ volts straight through it, but the joule thief part is not working, and I can't see the problem. As far as I can tell, everything looks just like the photos in the article, and I've run through the schematic over and over again, as well as taken the thing apart and put it back together several times.
  
  What are the common goof points (if any?)
  BTW, the solar battery part, which I soldered as a 6 pointed star with the photodiodes at each vertex, is putting out 27mV under the fuorescent shoplights, according to my crappy voltmeter - is that enough to drive the circuit once I get the joule thief part working?

  Posted by npkeith on December 07, 2009 at 07:04:56 Pacific Time

• troubleshooting...
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  Troubleshooting is a TOUGH one -- it helps if you can break the circuit down into single functional blocks.
  
  One block would be, for example, the LED, transistor, base resistor, and power supply (with a NEW resistor in series with the LED to limit current). Is the transistor oriented correctly? Is it the right kind? Does the LED light when a base voltage is applied?
  
  Then there is the inductor itself. If the two inductors (1-2 and 3-4) are wired in the wrong direction, the feedback will be reversed. Try reversing just one half of the inductor and see what happens.
  
  The PIN diode circuit is already separate, but the diode in series with it is important; a different diode may have a larger voltage drop, leaching away most if not all of the voltage that the diodes are raising.
  
  Once you can see voltage above and beyond the diode's drop, it still may take an hour or more to get an initial charge into the capacitor, depending on the strength of the light and the nature of the reverse diode.
  
  You mentioned the photo diodes in a six-pointed star... hopefully they are still wired in series, and not parallel! They must be, electrically, end to end and not side by side. When they are in series (as drawn in the article) their individual voltages add up to something useful. If they are in parallel, the currents will add up, which won't work here.
  
  Good luck!
  
  

  Posted by EdwinWiseOne on December 07, 2009 at 20:30:04 Pacific Time

• troubleshooting...
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  Thanks for the reply. I'll try your suggestions.
  Yes, the diodes are in series, I checked that three times as I was soldering (although I think your article said they could all be in parallel too. Hmm, putting six parallel pairs in series would look cool too... next time).
  
  So I do need to get a shottky diode for the solar battery part.
  
  I'm pretty sure I soldered the inductor correctly, (I did it three times after all...) but I'll check again. I used a 2N3904 from my sparkfun beginners kit just in case I fried the original transistor - that should work, right?

  Posted by npkeith on December 08, 2009 at 12:31:07 Pacific Time

• troubleshooting...
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  You could run multiple strands of diodes in parallel... boosting both voltage and current.
  
  The 2n3904 is somewhat similar to the BC549 in the article, though not quite as awesome... there's a good chance it would work anyway.
  
  The hard part with the inductor isn't just the soldering, but the knowing which pin goes where... in my experience, they tend to be marked poorly!

  Posted by EdwinWiseOne on December 08, 2009 at 14:13:00 Pacific Time