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.

• The current model will not see any major modifications and will be referred to as the Classic.  I like the sound of Edgerton One, but it would seem to be too similar to its most prolific competitor...  
  • The Classic will retain the same case design, 8-battery supply, and much of its controller design.  
  • The relay will be replaced with an opto-isolated P-channel MOSFET, the ringing in the MOSFET gates will be addressed, and a duration limiting circuit will be added.  
  • On completing these objectives, the design will be finalized and development will begin on the next sub-model.
• The next sub-model will be referred to as the Mark II. 
  • While the Classic was designed to be easily fabricated by anyone with a 3D printer and soldering skills, the Mark II will be designed with the potential for mass production in mind.  The components will be more optimized and may include hardware that isn't as easily assembled by hand.
  • The Mark II will retain the LED layout, driver circuitry, and (probably) the UI of the Classic.  
  • The primary design goal will be the ability to run from four AA batteries (3.2 - 6.0 V, 1.0 A max, 200 mA typical).  This will require a complete redesign of the electronics and modifications to the case design.