Major LED Failure!

A project log for Edgerton, A High-Speed LED Flash

Affordable photography tool used to capture images of bullets with no apparent motion blur

tyler-gerritsenTyler Gerritsen 06/03/2019 at 03:410 Comments

The Incident

After days of torture-testing a single LED before it even started to show evidence of damage, I managed to fry all twelve LED's in a single unintentional event.  That's $80 bucks of electronics GONE! 

I felt like Mark Watney from The Martian (the scene that happened in the novel but was sadly missing from the film...  If you read the book, you know the part).  To quote XKCD:

 I have never seen a work of fiction so perfectly capture the out-of-nowhere shock of discovering that you've just bricked something important because you didn't pay enough attention to a loose wire.

The event happened while I was experimenting with a switching regulator.  I hoped to decrease the number of AA batteries required, so I grabbed a boost regulator from eBay and set it to 12 volts.  Then powering the boost regulator from a 5V power supply, I started testing current draw during operation.  So the LED's functioned before these tests, but didn't work afterwards.

The saddest part is that I never even saw the final flash, since the unit was face-down on a table.  Some deduction leads me to infer that the LED's must have been cycled during the testing, during which time a power fluctuation must have occurred which caused the microcontroller to reset.  During the reset, the controller continued to activate the gate driver, resulting in a prolonged flash at 110 volts which resulted in complete failure of all twelve LED's.

Lessons Learned

The failure taught me two things.  

  1. The power supply system of Edgerton simply requires 8+ volts of battery voltage.  Using lower input votlages and a small boost regulator can cause catastrophic failure, and a high-capacity regulator will probably result in too much inefficiency.  
  2. A hardware circuit to prevent prolonged LED activation is more important than I first thought.  I investigated such a circuit before constructing Edgerton and didn't find a good solution.  But given the expensive loss of the components, I need to revisit the issue.

Future Actions Planned

Aside from the failure (which was a result of ill-planned testing), Edgerton has proven to be robust and functional.  However, I want to continue developing Edgerton to improve performance, reliability, and ease of use.  With that goal in mind, I've decided to eventually fork the project into two similar sub-models.