Morse code over laser light with an Arduino

19. After another of my famously lavish parties, I sometimes walk alone out to Promontory Point at exactly 10:00 p.m. Thursday and glance lakeward, out at a blinking light on some distant shore, and think of Daisy Buchanan. That light winks on and off, unattainable, a powerful metaphor for|wait, is that Morse code? [5 points for lights over a mile away; 15 points for lights over 5 miles away; 0 points for lights that are only metaphors] For this Scav Hunt item I used an Arduino to turn a laser pointer on and off in morse code:

#define pulseHigh(pin) {digitalWrite(pin, HIGH); digitalWrite(pin, LOW); }
#define RESET 13  // Pin 13 

void setup() {
pinMode(13, OUTPUT);
}

void loop() {
      
      digitalWrite(13,HIGH);
      delay (3000); 
      digitalWrite(13,LOW);
      delay (1500);
      dash();dash();dot();space();
      dot();dash();space();
      dot();dot();dot();space();
      dot();dot();dot();dot();space();
      delay(2000);
      
      
      pulseHigh(RESET); // off
};


void dot()
{
  digitalWrite(13,HIGH);
  delay(100);
  digitalWrite(13,LOW);
  delay(100);
  
}

void dash()
{
  digitalWrite(13,HIGH);
  delay(300);
  digitalWrite(13,LOW);
  delay(100);
  
}

void space()
{
  digitalWrite(13,LOW);
  delay(300);
}

I checked and saw at http://www.heywhatsthat.com/?view=PKDC86DD that the path from Adler Planetarium to the Point was just a touch over five miles and free. I could identify the Point fairly well in binoculars; I aimed the laser pointer by fixing to a tripod, testing the aiming by hitting nearer objects (a beach buoy nearby happened to be retroreflective which helped quite a bit) and then carefully moving the system towards the Point. I turned it off whenever boats went near the beam. To prove it was me, the judge requested I manually hit the key a few times--since I had only a programmed 'SCAV' (yes, it says GASH above), I manually connected the pointer to 5V & ground on the Arduino. It was powered via a 12V battery and a cigarette lighter USB charger to provide 5.1V.

3 Nano -- a video project

I created this project originally for the Sights and Sounds of Science contest which was sponsored by the Chicago Materials Research Center of the University of Chicago. This particular version was made for the Five-Minute Film Festival sponsored by NSIT.



Nanocrystals are small collections of several hundred to hundred thousand atoms arranged in a crystal matrix. Quantum dots are nanocrystals made of semiconductors, and the several hundred atoms act like one giant molecule with regards to their electrons with variations in energy levels due to the size of the dot. The smaller the dot, the higher photon energy released during fluorescence.

This video was compiled from fluorescing colloidal quantum dots of different sizes excited by an argon laser. The dots are invisible (with one exception in a microscope at 2:14) but they produce the bright colors in the beam. The bits of bright blue flashes are dust particles in the solutions.

The music is from Ms. John Soda, the song is "Technicolor" from the album No P. or D.

Pretty picture of the day

A dye laser points the way for the VLT towards the center of the galaxy.




Grab the huge versions of these at the ESO press page.
Seen via Astronomy Blog

Transmitting audio over light (laser or LED)

Want to send your audio information via a light wave across the room? I built this simple circuit with some modifications that transmits an audio signal via light. The signal simply amplitude modulates the light intensity (aka AM) of a LED and a receiving cadmium sulfide photocell changes its resistance as the intensity varies. Both sides have 8 to 1000 ohm audio transformers, although on my circuit I ended up using the transformer on the receiving side as a voltage booster. I also added a battery and resistor to the photocell receiving side.

Be careful--I used an LED because I destroyed a cheap laser pointer when trying the first circuit. The problem with it is the sound card audio is approximately 1 Volt AC at max, and this gets converted to ~12.5V on the other side (although I found output was usually around .5 V on the sound card and ~4 to 5V on the other side of the transformer). At least that's what I measured--I've seen people read 4V on sound cards, but I don't know which is correct.

I ended up using a white LED since it was my brightest LED, but I also have a superbright red LED that seems to work even better.







This is a 343KB video of the circuit in action. I block the beam and the sound volume dips.

I hate using the future tense on the web, so I'll say I promise to post a circuit diagram soon... --- and here it is! (keep in mind it's a CdS photocell, not a photodiode. I couldn't find the symbol in TinyCAD).

Forrest Mims wrote the book on this sort of thing, and there is a better circuit in Getting Started in Electronics, simply the best starter book for people interested in electronics and how things work.