Project Logs

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• Mark 2 - Development Update

  Tyler Gerritsen • 12/29/2019 at 15:43 • 0 comments

  The new high-speed flash is my pet project, but unfortunately it hasn't been at the top of my priority list recently.  Work and family life have used up most of my time, leaving very little for the Mark 2.  There have been a few developments recently and I wanted to share!

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  High-Power Lighting - WOW!

  I finally have a working offline driver for the LED's based on the DI AL9910 driver.  Three LED's can handle all of the power from a 144W power brick from Amazon, so sharing the load among all 12 LED's will result in a very long lifespan.

  Story time... I had three LED's powered up and was working on the unit.  So, I placed the LED's face-down on a shop towel.  Within two seconds I began to smell smoke... Turns out the shop towel was catching fire!  The LED's weren't even warm at this point, but the power output was enough to ignite paper!
  

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• Mark 2 - Development Update

  Tyler Gerritsen • 11/02/2019 at 02:08 • 0 comments

  Development is continuing!  Here are a few blurbs about recent design work.

  Control Board Design 95% Complete

  The main control board design has been generally completed.  A few minor tweaks need to be implemented (primarily related to the high-power DC converter, which hasn't been designed yet).  Some testing has been performed with the prototype board and the MIC2171 flyback converter I found on eBay
  

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• Control Board 1.2 Released

  Tyler Gerritsen • 09/29/2019 at 03:25 • 0 comments

  What's changed?

  1. Simplified External Trigger Protection - A single 1N4001 diode and two resistors protect the microcontroller from most causes of damage.  This protection circuit is cheaper and simpler than the V1.1 circuit, but much better than the V1.0 circuit.

  2. Solid-State Relay (SSR) Boost Control - Instead of the complex circuitry introduced in the V1.1 design, a single component is used to turn the high-voltage boost converter on and off.  The voltage drop on the load side is about 200 mV when driving the boost regulator, while it only uses less than 50 mA to run.  This is much better than earlier control circuits.  A number of SSR's will work, but I recommend the Vishay VO14642AT ($3.81 CAD on Digikey).
  3. Single Control Board - With the SSR mounted on the main control board, there is no need for a second control board for the boost converter.  This simplifies both construction and the wire routing inside the case.
  4. Pre-Built Control Boards Available For Purchase (SOON) - I've prototyped a control board and will have a small number manufactured soon for those who are interested in building a flash.  I hope to keep the price low with a slim profit margin to support my continuing experimentation with the LED's.

  What else is going on?

  Development of the Mark 2 is ongoing.  The control board has gone through several iterations, a handful of LED's have been destroyed with the powerful new circuitry, and I only wish that I had more time to devote to its development :)

  I'm also working on organizing an overview of my experiments for those who are interested in all the details.  The setup and results will be shared, likely on my website (www.td0g.ca).

  NQTRONIX has sent an active light probe which arrived a few weeks ago.  Sadly I haven't had time to experiment much with it, but hopefully soon I can begin collecting data to answer a number of questions.  I've built a crude integrating sphere to use with the probe.  Here's a teaser from the fooling around I've done so far:  The LED's appear to turn on REALLY REALLY fast and turn ALMOST off JUST AS FAST.  My claims of sub-microsecond pulsing will soon be proven with some oscilloscope traces!
  

• Mark 2 - Development Update

  Tyler Gerritsen • 08/13/2019 at 03:34 • 0 comments

  It's been some time since I posted about the continuing development of the Mark 2.  Progress has slowed recently as I've been distracted by a back injury, meanwhile my work and family have taken some priority over the project.  Here's a summary of the Mark 2 progress thus far:
  

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  Electronics

  The LED circuits have not changed at all.  The control board, however, has undergone a complete redesign.  One of the main goals was the ability to run on 4x AA batteries (3.2 - 6.0 Volts).  Realization requires three switching power converters (I purchased complete converter boards in order to save development time):

  • 3.3v converter for the control board (Pololu S7V8F3)
  • 15v converter for the gate driver (SX1308 Boost, purchased from eBay)
  • 125v capacitor charger (MIC2171 Flyback, purchased from eBay)

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• Tripwire Trigger System Functional

  Tyler Gerritsen • 07/01/2019 at 13:22 • 0 comments

  Various methods of triggering are available for high-speed photography, but the triggering systems are not cheap.  In an effort to make the hobby accessible and affordable, I've added a built-in triggering system that doesn't require any major hardware.  The 'Tripwire Triggering System' works by placing a special jig on the muzzle of the rifle.  A fine wire is positioned in front of the barrel, and when the projectile breaks the wire, Edgerton will strobe after a pre-programmed delay.

  Here's a photo with the triggering system set to 0 delay (triggering as soon as the tripwire is broken).  You can see the tripwire breaking just left of the projectile.

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• Edgerton V1.1 Released

  Tyler Gerritsen • 06/09/2019 at 15:14 • 0 comments

  What's New?

  The design for Edgerton has been updated to address several issues in the original design.  The circuit diagram, bill of materials, and 3D print files have been updated.  A new complete assembly manual has been written and made available.  The overall cost has increases slightly (less than $5) because of some new components.  Assembly requires a few more steps, but they are simple and the benefits greatly outweigh the cost and added assembly time.  Below is a brief overview of the changes and their rationale.

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  Reduced Power Consumption

  The microcontroller's isolation from the high-voltage boost converter is important to prevent resetting, and this was originally accomplished using a relay board purchased from eBay.  Unfortunately the relay drew several hundred milliamps, about as much as the boost regulator.  

  The relay has been replaced with a P-channel MOSFET, opto-isolator, and a couple resistors.  The new circuit draws about 30 mA - and may be reduced further with some optimization.  Isolation is maintained via the opto-isolator.  The cost has not increased and the circuit is easy to assembly and install.  A small benefit is the removal of the relay mount in the case, which means a reduction in filament usage.

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  Ferrite Beads for the Gates

  I previously noticed some significant ringing in the MOSFET gates.  Thanks to advice from a friendly German named Volker and guidelines presented in this application note from ON Semiconductor, I ordered some ferrite beads and installed them at the MOSFET gate leads.  Here's the gate signals before and after the ferrite beads were installed.

  The gate signal is cleaner.  Here's a trace showing how much the ferrite bead cleans up the signal.

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• Major LED Failure!

  Tyler Gerritsen • 06/03/2019 at 03:41 • 0 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.

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• Phosphor LED Turn-Off Time​

  Tyler Gerritsen • 06/01/2019 at 20:14 • 1 comment

  The Potential Problem

  I've received a few comments regarding the type of LED that Edgerton uses.  Specifically, the LED's may not turn off fast enough.  This is a problem I didn't really consider previously, given a statement in the Cree application note (pp. 10: The typical turn‑on time for an device is on the order of 10 nanoseconds or less).  Since they turn on in 10 ns, why can't they turn off as fast?

  Well, it turns out that the LED's use a little trick to make white light.  The actual LED modules make a blue light, and a layer of phosphor in front of the LED's turn the blue light into a spectrum of light ('white light').  While the LED's can turn on and off quickly, the phosphor is delayed in turning off (and maybe on - I don't know yet).  Notably, Edgerton's primary competition (Vela One) appears to use a similar type of LED and the manufacturer defends their flash durations on their website.

  Experimental Proof Of A Minor Problem

  Here's an experiment that demonstrates the problem.  It's a photograph of the LED flashing a 1-microsecond pulse.  There are three stages of the flashing cycle observed here:  The bright strip of light is the 1-microsecond flash, the illuminated dots above are the LED modules AFTER the flash, and the darker area below are the LED modules BEFORE the flash.

  Before explaining how this image works, I'll explain what it tells me.  The LED's above the flash strip show that there is some lag in turning off.  But during the turn-off time, the phosphor doesn't output much light.  In other words, the LED is incredibly bright for one microsecond, but then becomes dimly lit for some time afterward.

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• 150,000 Flashes Later

  Tyler Gerritsen • 05/29/2019 at 02:25 • 0 comments

  Strobing the LED's at several times their rated voltage is one thing, but a good flash needs to have a useful lifespan.  I began testing the lifespan of the unit a couple weeks ago.  Testing was done using only one LED (too expensive to risk multiple LED's) strobing at 1 hZ.  I started at 70 V, cycling 10,000 times at 1 microseconds and 5,000 times at 4 microseconds.  The LED was aimed at an 18% grey card 20 cm away and a DSLR photographed the card every 20th flash.  After the LED cycled 15,000 times I incremented the voltage +5 V and started again.  At 95 V, the LED showed no sign of quitting so I increased the flash rate to 2 hZ and photographed every 50th flash.

  Well, it turns out that the LED could handle all the way up to 125 V - and I stopped the test as the circuit board wasn't designed for more than that!  The photos were batch analyzed with ImageJ and no fluctuations in light output was observed.  Above is a photo of the LED with 150,000 flash cycles vs an LED that didn't go through the torture test (0.3 seconds vs >0.001 seconds total illumination time).  Interestingly a single element died at some point, but it still conducted current and light output was barely affected.
  

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• Voltage-Exposure Testing

  Tyler Gerritsen • 05/25/2019 at 19:33 • 0 comments

  Shortly after assembling the device, I tested a bank (3x LED's) by increasing the voltage until the LED's were damaged.  The test began at 45 V and incremented by 10 V following a single flash.  Major damage occurred at 125 V.

  More recently, I started a series of longevity tests with a single LED.  It was strobed over 100,000 times at various voltages.  Surprisingly, the LED reached 125 V and survived a battery of cycles at that voltage.

  Some head-scratching later and I realized that the FET driver was changed since the original destructive testing (TC4420 to TC4452).  The new driver could ground the MOSFET gates faster, shortening the pulse and probably preventing the LED from premature death.
  

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