Stroboscope 4.0: Encoder and High Power LED Integration

by tunafishsandwich

So it’s been a minute.  At this point I’ve added the following functionality:

  • Encoder based controls
  • 2x and 0.5x jump controls
  • 30 watts of LED based light

I’ve also ditched the current source LED driver board in favor a faster switching, harder driving solution.

I’ll start with a quick demo of how this thing works currently:

This video consists of me playing a 50 Hz test tone of a random youtube video through a loud speaker.  To start with, the strobe is flashing at 6272 Hz (i.e., slightly less than 2^7 x 50 Hz).  The speaker looks just like it normally would (a little blurry but generally stationary).  I then halve the strobe frequency 7 times to end up with a strobe frequency of 49 Hz.  At that point, what you see in the video is what appears to be a woofer cycling at 1 Hz, even though it is actually cycling at 50 Hz (too fast for the human eye to see).  That is the point of a stroboscope: to put high frequency periodic motion on the scale of human perception.

As mentioned earlier, the LED driver has been replaced with a simple MOSFET based circuit that gives me what appears to to rapid switching times and high power.  For the power supply, I’m using two 9v batteries via a LM7812 linear regulator giving me a VCC of 12v.  This drives the LED’s right at their limits (1000mA at 3.5v).  One reason for the change was that when flash pulses were set below 75 usec or so, there was no observable flash.  There also appeared to be a slight “ringing” in the brightness when the flashes were observable.  The inductance associated with the current regulating driver was probably the cause.  With the new circuit I can observe flashes down to commanded pulse widths of < 10 usecs.

Main code is here.  Library code for the Encoder class is here, and here.

So what’s next?  I want to package this into a compact, stand alone instrument.  That means:

  • Designing a few boards in Eagle
  • Getting said boards fabricated
  • Moving to a dedicated Microcontroller (vice Arduino)
  • Improving the frequency display (2×16 LCD vs seven segment LED display)
  • Adding a 5v trigger
  • Improving the control interface
  • Adding flash pulse width control

All for now.